1 Institute of Plant Sciences, Swiss Federal Institute of Technology, ETH
Centre, CH-8092 Zürich, Switzerland
2 Department of Plant and Microbial Biology, University of California, Berkeley,
CA 94720, USA
Author for correspondence at address1
(e-mail:wilhelm.gruissem{at}ipw.biol.ethz.ch)
Accepted 28 February 2003
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SUMMARY |
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Key words: Arabidopsis thaliana, Chromatin, MSI1, RbAp48, AGAMOUS, Meristem, Ovule
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INTRODUCTION |
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Unlike in most animals, environmental factors strongly affect development
of plants. Although the differences in developmental strategies are striking,
it now emerges that plants utilise molecular mechanisms similar to those that
control animal development (Habu et al.,
2001; Verbsky and Richards,
2001
; Meyerowitz,
2002
). For example, chromatin-modifying proteins such as histone
deacetylases, several polycomb-group proteins, like-heterochromatin protein 1,
and chromatin assembly factor 1 (CAF-1) are also required for normal plant
development (Goodrich et al.,
1997
; Chaudhury et al.,
1997
; Grossniklaus et al.,
1998
; Wu et al.,
2000
; Tian and Chen,
2001
; Gaudin et al.,
2001
; Kaya et al.,
2001
). Proteins similar to yeast MSI1 (multicopy suppressor of
ira1) and to the mammalian retinoblastoma-associated proteins
RbAp46/48 are WD40 repeat proteins encoded by small multigene families in most
eukaryotes. These conserved proteins are components of complexes involved in
chromatin metabolism, including CAF-1, pRb, histone acetyl transferases and
histone deacetylases (Qian et al.,
1993
; Parthun et al.,
1996
; Verreault et al.,
1996
; Taunton et al.,
1996
). CAF-1, a trimeric complex that facilitates deposition of
nucleosomes on newly synthesised DNA, has been identified in
Arabidopsis, mammals, yeast, flies and Xenopus
(Smith and Stillman, 1989
;
Bulger et al., 1995
;
Kaufman et al., 1997
;
Quivy et al., 2001
;
Kaya et al., 2001
).
Biochemical analysis has shown that, similar to their animal counterparts,
plant MSI1-like proteins are found in CAF-1 and can bind to plant
retinoblastoma-related proteins and histones
(Ach et al., 1997
;
Kaya et al.,2001
;
Rossi et al., 2001
). The
biochemical data have not provided substantial insights into the biological
function of MSI1-like proteins. Loss of MSI1 function in yeast does not
produce apparent phenotypic alterations under optimal growth conditions.
Detailed molecular analysis of msi1 mutants revealed, however, that
silencing of telomeric regions and mating type loci is decreased and cells are
more sensitive to UV light (Kaufman et
al., 1997
). The functional analysis of MSI1-like proteins has
proved more difficult in multicellular eukaryotes. The mutation lin53
in Caenorhabditis elegans revealed that LIN53 encodes a
MSI1-like protein, which interacts with the retinoblastoma-like LIN35 protein
and is required during vulva formation (Lu
and Horvitz, 1998
). RNAi-mediated interference with LIN53
expression caused embryo lethality, suggesting that the gene product has an
essential function during development. Additional mutants that affect
MSI1-like proteins in other organisms could therefore provide important new
insights into the function of this family of WD40 proteins in yeast and
multicellular eukaryotes.
Four MSI1-like proteins have been identified in Arabidopsis
(AtMSI1-4), but only AtMSI1 is most similar to RbAp48
(Ach et al., 1997;
Kenzior and Folk, 1998
).
Similar to MSI1-like proteins from mammals, Drosophila and yeast,
AtMSI1 and its tomato homologue LeMSI1 are predominantly localised to the
nucleus (Quian et al., 1993; Tyler et
al.,1996
; Ach et al.,
1997
; Zhu et al.,
2000
; Bouché et al.,
2002
). A direct biological role, however, has not been established
for either mammalian or plant MSI1-like proteins. Here we show that reducing
AtMSI1 expression in Arabidopsis disrupts several aspects of
the developmental program. Our results suggest that AtMSI1 function is
required during vegetative and reproductive growth and for maintenance of
correct homeotic gene expression.
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MATERIALS AND METHODS |
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Protein gel blot analysis
Protein extracts were prepared from Arabidopsis by grinding fresh
or frozen tissue in extraction buffer (100 mM Tris, pH 7.5, 500 mM NaCl, 5 mM
EDTA, 10 mM EGTA, 10% sucrose, 40 mM b-mercaptoethanol, 0.5 mg/ml Pefablock SC
(Roche, Rotkreuz, Switzerland), 1 µg/ml pepstatin, 0.5 µg/ml leupeptin,
40 µg/ml bestatin. Homogenates were centrifuged for 5 minutes at 14,000
g and 4°C. SDS-PAGE, protein blotting and detection were
performed as described previously (Ach et
al., 1997). Chemiluminescent detection was performed with ECL
(Amersham, Uppsala, Sweden) according to manufacturer's instructions.
Production of AtMSI1-5 fusion proteins
For coupled in vitro transcription and translation reactions, cDNAs of
AtMSI1-5 were cloned in frame with the HA-tag in pGADT7 (Clonetech,
Palo Alto, CA). Reactions were performed using a Promega TnT wheat germ
extract system (Promega, Madison, WI) according to manufacturer's
instructions.
RNA isolation and RT-PCR
RNA was extracted from leaves of 4-week-old plants using Trizol
(Invitrogen, Carlsbad, CA) according to manufacturer's instructions.
Fractionation of RNA on an agarose gel, transfer to nylon membranes,
hybridisation with a random-primed 32P-labelled probe and detection
were performed as described previously (Ach
et al., 1997). For RT-PCR analysis, 1 µg total RNA was treated
with DNase I. Half of the DNA-free RNA (0.5 µg) was reverse-transcribed
using an oligo(dT) primer and MMLV reverse transcriptase (Clonetech, Palo
Alto, CA), while the remaining RNA was incubated without reverse
transcriptase. Aliquots of the generated cDNA, which equalled 50 ng total RNA,
were used as template for PCR with gene specific primers
(Table 1).
|
Cytological analysis
Samples were prepared according to the method of Ross et al.
(Ross et al., 1996). Briefly,
inflorescences were fixed in ethanol:acetic acid (3:1), washed in water and
incubated for 2 hours at 37°C with 0.3% (w/v) each of cellulase,
pectolyase and cytohelicase in 10 mM sodium citrate (pH 4.5) to remove cell
walls. Nuclei from petals were spread on microscopic slides as described, and
stained with 4',6'-diamidino-2-phenylindole (DAPI). The
fluorescence patterns were examined with a Zeiss Axioplan microscope, and
images were recorded with an MagnaFire® CCD camera (Optronics, Goleta,
CA). Digital images were quantified using ImageJ 1.27Z (W. Rasband, NIH, USA,
http://rsb.info.nih.gov/ij/).
Total fluorescence was determined for at least 40 representative nuclei.
Regions corresponding to chromocentres were selected manually and their
emitted fluorescence was quantified.
Computational methods
Sequences were aligned using CLUSTAL_X
(Thompson et al., 1997) with
default settings. Using the neighbour-joining algorithm implemented in
CLUSTAL_X, an N-J tree was constructed that was corrected for multiple
substitutions. The tree was bootstrapped and a graph of the tree was displayed
using TreeView software (Page,
1996
).
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RESULTS |
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Phylogenetic analysis of selected MSI1-like proteins from plants, yeast and animals demonstrated that diversification of these proteins occurred independently several times in evolution (Fig. 1). We were unable to identify a clade containing MSI1-like proteins that could be used to predict a specific biochemical function. When proteins from chicken and Xenopus were included in the analysis, we obtained similar results and found that the additional sequences grouped more closely with the human proteins RbAp46 and RbAp48, and Drosophila p55. In plants, divergence of MSI1-like proteins most likely occurred before the monocot and dicot split, because AtMSI1, AtMSI4 and AtMSI5 have close relatives in the monocot corn (Zea mays). AtMSI2/AtMSI3 and AtMSI4/AtMSI5 form pairs of very similar proteins (similarity of 90% and 83%, respectively), suggesting that the proteins are functionally redundant. Since AtMSI1 is sufficiently diverged from the other proteins, we expected that altering expression of AtMSI1 would likely provide new insights into the function of this WD40 protein.
|
|
Among the progeny of ten of the original 70 T1
AtMSI1-OE plants, including 1OEa3 and 1OEc2, several plants developed
a severely stunted phenotype and were sterile. To determine the level of
AtMSI1 protein accumulation in this class of AtMSI1-OE plants,
protein extracts were prepared from rosette leaves of T3 siblings and
subjected to gel blot analysis. Fig.
2D shows results from six 1OEa3 plants as an example. In plants
that had stunted growth, AtMSI1 protein levels were reduced to less than 10%
of control plants (Fig. 2D, lanes 3, 4 and 6). Siblings that appeared normal accumulated either wild-type
(lane 2) or strongly increased AtMSI1 levels (lanes 7 and 8). Similar results
were obtained for 1OEc2 T3 siblings (data not shown). The reduction of AtMSI1
levels in these plants was most likely the result of co-suppression of
transgene and endogenous gene expression
(Matzke and Matzke, 1995).
Co-suppression of AtMSI1 was gene specific, as would be expected
based on the limited amino acid sequence homology with AtMSI2-5. RT-PCR with
cDNA-specific primers demonstrated that mRNA levels of AtMSI2-5 were
not decreased in the AtMSI1-OE co-suppressed (subsequently termed
AtMSI1-CS) plants (Fig.
2E). The strong AtMSI1 co-suppression phenotype was
recovered in 10-30% of the progeny of at least 3 independently transformed
plants, and AtMSI1-CS plants from lines 1OEc2 and 1OEa3 showed a
similar phenotype for all aspects that were subsequently analysed.
Co-suppression of AtMSI1 strongly affects plant
development
The rosette leaves of AtMSI1-CS plants were irregular in shape,
and the normal phylotactic pattern of leaf production from the shoot apical
meristem was altered (Fig.
3A,B).
After transition to flowering, the primary shoot of wild-type plants elongated
and formed cauline leaves, lateral branches and flowers
(Fig. 3C, left). In contrast,
the primary shoot of AtMSI1-CS plants arrested early in development
(Fig. 3C, right and
Fig. 3D). After elongating for
5 to 15 mm, some shoots formed one or two aborted floral buds, but more
frequently no organs developed except some bract-like structures.
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AtMSI1-CS plants contain reduced amounts of
heterochromatin
Arabidopsis chromocentres contain highly condensed heterochromatic
DNA that consists of centromeric and pericentomeric repeats and rRNA genes
(Maluszynska and Heslop-Harrison,
1991; Fransz et al.,
2002
). Formation of chromocentres requires epigenetic imprints,
such as DNA methylation and histone acetylation, because reduced amounts of
heterochromatin and dispersion of pericentromeric sequences away from
chromocentres were observed in decreased DNA methylation 1
(ddm1) and met1 mutants
(Soppe et al., 2002
). Because
AtMSI1 most likely participates in specific chromatin-modifying complexes, it
could also be required for maintenance of functional heterochromatin. We
therefore investigated the structure of nuclei in AtMSI-CS plants
that had strongly reduced AtMSI1 levels using nuclear spreads and compared
them to wild-type nuclei. The general appearance of AtMSI-CS
interphase nuclei, including nuclear size and number of chromocentres, was not
significantly different (Fig.
8). We quantified nuclear fluorescence originating from
heterochromatic chromocentres and from the remaining euchromatic regions of
nuclei. In wild-type interphase nuclei, euchromatin fluorescence was 2.3 times
higher than heterochromatin fluorescence. In contrast, this ratio increased to
4.0 in AtMSI1-CS plants (Fig.
8B, right). These observations indicate that recruitment of
chromosomal DNA into heterochromatic chromocentres is strongly reduced in the
absence of AtMSI1.
|
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DISCUSSION |
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AtMSI1 is not functionally redundant with AtMSI2-5
Reduced levels of AtMSI1 altered cotyledon and leaf shape, affected
meristem function, and reduced fertility, indicating that AtMSI1 function is
required during vegetative and reproductive development. This conclusion is
consistent with the presence of AtMSI1 in all tissues and organs that were
analysed. Moreover, AtMSI1 was expressed most strongly in flowers, which were
also most severely affected by reduced AtMSI1 levels in AtMSI1-CS
plants. RT-PCR with gene-specific primers confirmed that AtMSI2-5
mRNA levels were not reduced in AtMSI1-CS plants. The morphological
changes are therefore strictly correlated with the changes in AtMSI1 levels,
suggesting that there is only limited functional redundancy between AtMSI1 and
the other four MSI1-like proteins in Arabidopsis.
AtMSI1 may function in multiple chromatin-modifying complexes
A CAF-1 complex active in chromatin assembly in vitro is also present in
Arabidopsis and consists of FAS1, FAS2 and AtMSI1, which are similar
to CAC1, CAC2 and CAC3 (Kaya et al.,
2001). FAS1 or FAS2 are both encoded by single copy genes in
Arabidopsis. Mutations in these genes cause fasciation as the result
of an enlarged shoot apical meristem. Fasciated plants have an altered
phyllotaxy and leaf shape, reduced root growth, broadened, flattened or
bifurcated stems and increased numbers of flower organs
(Reinholz, 1966
;
Leyser and Furner, 1992
).
Despite strongly reduced AtMSI1 protein levels AtMSI1-CS plants
showed only mild symptoms of fasciation. It is possible that the AtMSI1 levels
still present in these plants are sufficient to maintain minimal CAF-1
activity for functional chromatin assembly. Alternatively, one of the other
MSI1-like proteins in Arabidopsis (AtMSI2-5) can substitute for
AtMSI1 function in CAF-1 activity. AtMSI1-CS plants also have several
phenotypic alterations not associated with the fasciation phenotype in
fas1 and fas2, and repression of AG and
AP2 expression in leaves is lost when AtMSI1 is strongly reduced, but
not when FAS1 and FAS2 are absent. Because Arabidopsis accessions are
known to differ in genetic potential and developmental programs
(Alonso-Blanco and Koornneef,
2000
), both the fas1-1 and the fas2-1 allele
were back-crossed into the Columbia accession. However, the different
phenotypes of AtMSI1-CS and fasciata mutants remained
independent of the genetic background (data not shown). Therefore, AtMSI1
functions not only in CAF-1 but also in other chromatin-modifying complexes
that do not contain the two larger CAF-1 subunits. Studies on MSI1-like
proteins in yeast and animals suggest potential biochemical functions
involving histone acetylation, deacetylation or methylation and nucleosome
remodelling (Tyler et al.,
1996
; Martinez-Balbas et al.,
1998
; Tie et al.,
2001
; Czermin et al.,
2002
). Protein binding studies revealed that AtMSI1 interacts with
the Arabidopsis retinoblastoma-related protein (RBR) and histone
deacetylase HDA1, and that AtMSI2 and AtMSI3 interact with FAS1 (Heidi Feiler,
Lars Hennig, N. S., P. T. and W. G., unpublished data). Together, our data
suggest AtMSI1-5 have different functional specificities. While some of the
functions depend strictly on AtMSI1, other functions (e.g., CAF-1 mediated
chromatin assembly) could also involve AtMSI2-5.
AtMSI1 is required for the maintenance of meristem function
AtMSI1 deficiency affects the shoot apical meristem, and both floral
meristems and primordia. The fate of the primary shoot meristem after
transition to flowering was strongly dependent on AtMSI1 levels. While leaf
development during the vegetative phase was affected but not abrogated,
essentially no organs developed on the AtMSI1-CS primary shoot after
transition to flowering. The appearance of bract-like structures demonstrated
that primordia could be initiated by the inflorescence shoot apical meristem,
but were unable to differentiate correctly. Secondary inflorescence shoots
arising from axillary meristems of rosette leaves were significantly less
affected and only occasionally showed a developmental arrest similar to the
primary inflorescence shoot. Although the secondary inflorescence shoots
usually gave rise to bracts, flowers and lateral shoots, flowers formed on
these shoots displayed a progressive loss of floral morphology. As with leaf
development during the vegetative phase, flower organs appeared to initiate
normally, but their normal differentiation was disrupted. Since the severity
of phenotypes increased with additional rounds of cell divisions, perhaps
AtMSI1 is required to maintain the epigenetically controlled developmental
pattern of gene expression during cell division.
Sterility of AtMSI1-CS plants is caused by defects in ovule
development
In wild-type Arabidopsis plants, ovule development comprises
primordia initiation, specification of identity, pattern formation,
morphogenesis and cellular differentiation
(Grossniklaus and Schneitz,
1998; Schneitz,
1999
). Ovules arise as finger-like protrusions from the placental
tissue of the carpel. After polarity has been established along a
proximal-distal (PD) axis of symmetry, megasporogenesis begins and the two
integuments initiate. Outgrowth of the outer integument shows strong polarity
along the adaxial-abaxial (Ad-Ab) axis, which results in anatropy of mature
ovules. Similar to leaf and flower development, initiation of ovule primordia
and the integuments occurred normally. Loss of AtMSI1 did not affect polarity
along the PD and Ad-Ab axis, but prevented further asymmetric growth and
megagametogenesis. Several genes whose functions are required during ovule
development have been identified already (for review, see
Grossniklaus and Schneitz,
1998
; Schneitz,
1999
). In addition to ovule-specific genes, genes involved in
other developmental processes are also required for proper ovule development.
Among them SUP, AG, WUS and SPLAYED (SPY) are
noteworthy, since mutants defective in these genes, or lines in which these
genes are ectopically expressed, share several morphological alterations with
AtMSI1-CS plants (Ray et al.,
1994
; Gaiser et al.,
1995
; Western and Haughn,
1999
; Groß-Hardt et al.,
2002
; Wagner and Meyerowitz,
2002
). In particular, ovule development arrests at similar stages
in spy mutants and AtMSI1-CS. SPY is a SWI/SNF ATPase
homolog, which is thought to modify activity of the LFY transcription factor
by altering chromatin states, and AG is among the genes whose
expression depends on LFY and SPY activity
(Wagner and Meyerowitz, 2002
).
Given the phenotypic aspects shared among the mutants, it will be interesting
to test possible genetic interactions between SPY and
AtMSI1.
Reduction of AtMSI1 function activates the ectopic expression of
homeotic genes that control meristem fate
In AtMSI1-CS plants, reduction of AtMSI1 levels disrupts the
spatial and temporal control of expression for several homeotic genes that
regulate plant development and organ identity. The class C floral organ
identity gene AG, whose expression is confined to the inner two
whorls of flowers in wild-type Arabidopsis, was ectopically expressed
in leaves of AtMSI1-CS plants. AP2, a class A floral organ
identity gene that is also expressed weakly in leaves
(Jofuku et al., 1994;
Okamuro et al., 1997
), was
more strongly expressed in leaves of AtMSI1-CS plants than in
wild-type plants. Expression of WUS, AP1, AP3 and SUP was
not affected in AtMSI1-CS plants, suggesting that loss of AtMSI1
function affects only a selected class of regulatory genes. Aberrant
expression of AG is not restricted to leaves, and activity of the
AG::GUS reporter in AtMSI1-CS flowers is also consistent
with the observed homeotic changes of organ identity. GUS activity was
detected in the tips of enlarged sepals that acquired a carpel-like, abnormal
identity characterised by stigmatic structures. GUS staining was much weaker
in AtMSI1-CS leaves and was concentrated along the leaf veins (data
not shown). Thus, transcriptional control of both the endogenous AG
gene and also the reporter transgene depends on AtMSI1 function.
AP2 and AG are known to interact antagonistically and
reciprocally inhibit their activation in floral whorls
(Bowman et al., 1991). Because
AP2 and AG expression domains overlap also in whorl 3 and
whorl 4 of WT flowers, AP2 and AG gene products are not sufficient for
transcriptional repression (Jofuku et al.,
1994
). Therefore, the simultanous expression of both AP2
and AG in AtMSI1-CS leaves is quite conceivable. Current
models suggest that homeotic genes, which control the developmental fate of
meristems, are controlled by modulation of their chromatin structures and/or
methylation status (Conner and Liu,
2000
; Jacobsen et al.,
2000
; Tian and Chen,
2001
; Yoshida et al.,
2001
; Wagner and Meyerowitz,
2002
). For example, AG, AP3 and SUP are
ectopically expressed in mutants such as clf, met1 and others
(Finnegan et al., 1996
;
Goodrich et al., 1997
). Thus,
it is possible that the higher-order chromatin structure or assembly of
specific repressor complexes at promoters of AG and AP2
depend, either directly or indirectly, on AtMSI1 function. Notably, this
function is independent of chromatin assembly by CAF-1 because even the
fas1 fas2 double mutant maintains the repressed state of AG
and AP2 in leaves.
Reduced AtMSI1 levels alter nuclear chromatin organisation
The functional analysis of AtMSI1 discussed above suggests that the protein
may have a role in control of chromatin structure and dynamics. Our
cytological analysis of AtMSI-CS nuclei subsequently revealed a
significant loss of heterochromatin assembly into chromocentres. Recent
reports have established a central role of nuclear chromocentres for the
organisation of chromosomal DNA, and specific euchromatic loops were detected
that extended from the condensed heterochromatin
(Fransz et al., 2002;
Soppe et al., 2002
). In
contrast to the DNA in such loops, DNA present in chromocentres was heavily
methylated. Similar to our observations in AtMSI1-CS nuclei,
ddm1 and met1, which both have reduced DNA methylation, also
had smaller chromocentres. Methylation is a genomic imprint that is required
for the maintenance of heterochromatin
(Soppe et al., 2002
).
Strikingly, both met1 and AtMSI1-CS plants assemble less DNA
into chromocentres, ectopically express AG and other floral homeotic
genes, and share other phenotypic traits
(Finnegan et al., 1996
;
Soppe et al., 2002
; this
study). We therefore tested if methylation of centromeric repeats, which is
strongly decreased in met1 plants, was affected in
AtMSI1-CS. Blots of genomic DNA digested with methylation-sensitive
or -insensitive restriction endonucleases demonstrated, however, that
centromeric methylation patterns were intact in AtMSI1-CS plants
(data not shown). In summary, we propose that AtMSI1 is required downstream of
DDM1- and MET1-dependent DNA methylation in order to facilitate formation of
repressive chromatin structures. Alternatively, AtMSI1 might function in a
pathway parallel to DNA methylation. Experiments are in progress to establish
the role of AtMSI1 in heterochromatin condensation.
The extent of the phenotypic alterations that resulted from the reduction
and loss of AtMSI1 function suggests that AtMSI1 has a fundamental role in
development and cellular differentiation. Our view is consistent with the
report that RNA-mediated interference (RNAi) of LIN53 expression,
which encodes a protein similar to RbAp48 and MSI1, causes embryonic lethality
in C. elegans (Lu and Horvitz,
1998). It is important to note, however, that not all
developmental processes are similarly affected in plants with reduced AtMSI1
levels. The role of AtMSI1 in specific developmental pathways will be
understood better once the significance of its interactions with the
retinoblastoma tumour suppressor protein, HDA-dependent transcriptional
co-repressors, CAF-1, NURF and perhaps other chromatin-modifying complexes has
been analysed in more detail. It will also be important to clarify the
function of the other MSI1-like proteins in Arabidopsis, which may
provide new insights into the biological functions of this class of WD40
proteins in other multicellular eukaryotes as well.
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ACKNOWLEDGMENTS |
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![]() |
Footnotes |
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REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Ach, R. A., Taranto, P. and Gruissem, W.
(1997). A conserved family of WD-40 proteins binds to the
retinoblastoma protein in both plants and animals. Plant
Cell 9,1595
-1606.
Alonso-Blanco, C. and Koornneef, M. (2000). Naturally occurring variation in Arabidopsis: an underexploited resource for plant genetics. Trends Plant Sci. 5, 22-29.[CrossRef][Medline]
The Arabidopsis Genome Initiative (2000). Analysis of the genome sequence of the flowering plant Arabidopsis thaliana. Nature 408,796 -815.[CrossRef][Medline]
Bouché, N., Scharlat, A., Snedden, W., Bouchez, D. and
Fromm, H. (2002). A novel family of calmodulin-binding
transcription activators in multicellular organisms. J. Biol.
Chem. 277,21851
-21861.
Bowman, J. L., Smyth, D. R. and Meyerowitz, E. M. (1991). Genetic interactions among floral homeotic genes of Arabidopsis. Development 112, 1-20.[Abstract]
Bulger, M., Ito, T., Kamakaka, R. T. and Kadonaga, J. T. (1995). Assembly of regularly spaced nucleosome arrays by Drosophila chromatin assembly factor 1 and a 56-kDa histone-binding protein. Proc. Natl. Acad. Sci. USA 92,11726 -11730.[Abstract]
Czermin, B., Melfi, R., McCabe, D., Seitz, V., Imhof, A. and Pirrotta, V. (2002). Drosophila Enhancer of Zeste/ESC Complexes Have a Histone H3 Methyltransferase Activity that Marks Chromosomal Polycomb Sites. Cell 111,185 -196.[Medline]
Chaudhury, A. M., Ming, L., Miller, C., Craig, S., Dennis, E. S.
and Peacock, W. J. (1997). Fertilization-independent seed
development in Arabidopsis thaliana. Proc. Natl. Acad.
Sci. USA 94,4223
-4228.
Clough, S. J. and Bent, A. F. (1998). Floral dip: a simplified method for Agrobacterium-mediated transformation of Arabidopsis thaliana. Plant J. 16,735 -743.[CrossRef][Medline]
Conner, J. and Liu, Z. (2000). LEUNIG, a
putative transcriptional corepressor that regulates AGAMOUS expression during
flower development. Proc. Natl. Acad. Sci. USA
97,12902
-12907.
Fransz, P., De Jong, J. H., Lysak, M., Castiglione, M. R. and
Schubert, I. (2002). Interphase chromosomes in Arabidopsis
are organized as well defined chromocenters from which euchromatin loops
emanate. Proc. Natl. Acad. Sci. USA
99,14584
-14589.
Finnegan, E. J., Peacock, W. J. and Dennis, E. S.
(1996). Reduced DNA methylation in Arabidopsis thaliana
results in abnormal plant development. Proc. Natl. Acad. Sci.
USA 93,8449
-8454.
Gaiser, J. C., Robinson-Beers, K. and Gasser, C. S.
(1995). The Arabidopsis SUPERMAN gene mediates
asymmetric growth of the outer integument of ovules. Plant
Cell 7,333
-345.
Gaudin, V., Libault, M., Pouteau, S., Juul, T., Zhao, G.,
Lefebvre, D. and Grandjean, O. (2001). Mutations in LIKE
HETEROCHROMATIN PROTEIN 1 affect flowering time and plant architecture in
Arabidopsis. Development
128,4847
-4858.
Goodrich, J., Puangsomlee, P., Martin, M., Long, D., Meyerowitz, E. M. and Coupland, G. (1997). A Polycomb-group gene regulates homeotic gene expression in Arabidopsis. Nature 386,44 -51.[CrossRef][Medline]
Groß-Hardt, R., Lenhard, M. and Laux, T.
(2002). WUSCHEL signaling functions in interregional
communication during Arabidopsis ovule development. Genes
Dev. 16,1129
-1138.
Grossniklaus, U. and Schneitz, K. (1998). The molecular and genetic basis of ovule and megagametophyte development. Semin. Cell. Dev. Biol. 9, 227-238.[CrossRef][Medline]
Grossniklaus, U., Vielle-Calzada, J. P., Hoeppner, M. A. and
Gagliano, W. B. (1998). Maternal control of embryogenesis by
MEDEA, a polycomb group gene in Arabidopsis.
Science 280,446
-450.
Habu, Y., Kakutani, T. and Paszkowski, J. (2001). Epigenetic developmental mechanisms in plants: molecules and targets of plant epigenetic regulation. Curr. Opin. Genet. Dev. 11,215 -220.[CrossRef][Medline]
Jacobsen, S. E., Sakai, H., Finnegan, E. J., Cao, X. and Meyerowitz, E. M. (2000). Ectopic hypermethylation of flower-specific genes in Arabidopsis. Curr. Biol. 10,179 -186.[CrossRef][Medline]
Jofuku, K. D., den Boer, B. G., van Montagu, M. and Okamuro, J.
K. (1994). Control of Arabidopsis flower and seed development
by the homeotic gene APETALA2. Plant Cell
6,1211
-1225.
Kaufman, P. D., Kobayashi, R. and Stillman, B. (1997). Ultraviolet radiation sensitivity and reduction of telomeric silencing in Saccharomyces cerevisiae cells lacking chromatin assembly factor-I. Genes Dev. 11,345 -357.[Abstract]
Kaya, H., Shibahara, K., Taoka, K., Iwabuchi, M., Stillman, B. and Araki, T. (2001). FASCIATA genes for chromatin assembly factor-1 in Arabidopsis maintain the cellular organization of apical meristems. Cell 104,131 -142.[Medline]
Kenzior, A. L. and Folk, W. R. (1998). AtMSI4 and RbAp48 WD-40 repeat proteins bind metal ions. FEBS Lett. 440,425 -429.[CrossRef][Medline]
Koncz, C. and Schell, J. (1986). The promoter of TL-DNA gene 5 controls the tissue specific expression of chimaeric genes carried by a novel type of Agrobacterium binary vector. Mol. Gen. Genet. 204,383 -396.
Leyser, H. M. O. and Furner, I. J. (1992).
Characterisation of three shoot apical meristem mutants of Arabidopsis
thaliana. Development
116,397
-403.
Lu, X. W. and Horvitz, H. R. (1998). lin-35 and lin-53, two genes that antagonize a C. elegans Ras pathway, encode proteins similar to Rb and its binding protein RbAp48. Cell 95,981 -991.[Medline]
Maluszynska, J. and Heslop-Harrison, J. S. (1991). Localisation of tandemly repeated DNA sequences in Arabidopsis thaliana. Plant J. 1, 159-166.[CrossRef]
Martinez-Balbas, M. A., Tsukiyama, T., Gdula, D. and Wu, C.
(1998). Drosophila NURF-55, a WD repeat protein involved in
histone metabolism. Proc. Natl. Acad. Sci. USA
95,132
-137.
Matzke, M. A. and Matzke, A. J. M. (1995). How
and why do plants inactivate homologous (trans)genes? Plant
Physiol. 107,679
-685.
Meyerowitz, E. M. (2002). Plants compared to
animals: the broadest comparative study of development.
Science 295,1482
-1485.
Muller, C. and Leutz, A. (2001). Chromatin remodeling in development and differentiation. Curr. Opin. Genet. Dev. 11,167 -174.[CrossRef][Medline]
Narlikar, G. J., Fan, H. Y. and Kingston, R. E. (2002). Cooperation between complexes that regulate chromatin structure and transcription. Cell 108,475 -487.[Medline]
NASC On-Line Catalogue. Internet WWW page at http://nasc.nott.ac.uk/home.html.
Okamuro, J. K., Caster, B., Villarroel, R., van Montagu, M. and
Jofuku,K. D. (1997). The AP2 domain of APETALA2
defines a large new family of DNA binding proteins in Arabidopsis.
Proc. Natl. Acad. Sci. USA
94,7076
-7081.
Page, R. D. (1996). TreeView: an application to display phylogenetic trees on personal computers. Comput. Appl. Biosci. 12,357 -358.[Medline]
Parthun, M. R., Widom, J. and Gottschling, D. E. (1996). The major cytoplasmic histone acetyltransferase in yeast: links to chromatin replication and histone metabolism. Cell 87,85 -94.[Medline]
Qian, Y. W., Wang, Y. C., Hollingsworth, R. E., Jr, Jones, D., Ling, N. and Lee, E. Y. (1993). A retinoblastoma-binding protein related to a negative regulator of Ras in yeast. Nature 364,648 -652.[CrossRef][Medline]
Quivy, J. P., Grandi, P. and Almouzni, G.
(2001). Dimerization of the largest subunit of chromatin assembly
factor 1: importance in vitro and during Xenopus early development.
EMBO J. 20,2015
-2027.
Ray, A., Robinson-Beers, K., Ray, S., Baker, S. C., Lang, J. D., Preuss, D., Milligan, S. B. and Gasser, C. S. (1994). Arabidopsis floral homeotic gene BELL (BEL1) controls ovule development through negative regulation of AGAMOUS gene (AG). Proc. Natl. Acad. Sci. USA 91,5761 -5765.[Abstract]
Reinholz, E. (1966). Radiation induced mutants showing changed inflorescence characteristics. Arabid. Inf. Serv. 3,19 -20.
Reyes, J. C., Hennig, L. and Gruissem, W.
(2002). Chromatin remodeling and memory factors new
regulators of plant development. Plant Physiol.
130,1090
-1101.
Ross, K., Fransz, P. F. and Jones, G. H. (1996). A light microscopic atlas of meiosis in Arabidopsis thaliana. Chromosome Res. 4, 507-516.[Medline]
Rossi, V., Varotto, S., Locatelli, S., Lanzanova, C., Lauria, M., Zanotti, E., Hartings, H. and Motto, M. (2001). The maize WD-repeat gene ZmRbAp1 encodes a member of the MSI/RbAp sub-family and is differentially expressed during endosperm development. Mol. Genet. Genomics 265,576 -584.[CrossRef][Medline]
Schneitz, K. (1999). The molecular and genetic control of ovule development. Curr. Opin. Plant. Biol. 2, 13-17.[CrossRef][Medline]
Sieburth, L. E. and Meyerowitz, E. M. (1997).
Molecular dissection of the AGAMOUS control region shows that cis elements for
spatial regulation are located intragenically. Plant
Cell 9,355
-365.
Smith, S. and Stillman, B. (1989). Purification and characterization of CAF-I, a human cell factor required for chromatin assembly during DNA replication in vitro. Cell 58, 15-25.[Medline]
Soppe, W. J., Jasencakova, Z., Houben, A., Kakutani, T.,
Meister, A., Huang, M. S., Jacobsen, S. E., Schubert, I. and Fransz, P. F.
(2002). DNA methylation controls histone H3 lysine 9 methylation
and heterochromatin assembly in Arabidopsis. EMBO
J. 21,6549
-6559.
Taunton, J., Hassig, C. A. and Schreiber, S. L. (1996). A mammalian histone deacetylase related to the yeast transcriptional regulator Rpd3p. Science 272,408 -411.[Abstract]
Thompson, J. D., Gibson, T. J., Plewniak, F., Jeanmougin, F. and
Higgins, D. G. (1997). The CLUSTAL_X windows interface:
flexible strategies for multiple sequence alignment aided by quality analysis
tools. Nucleic Acids Res.
25,4876
-4882.
Tian, L. and Chen, Z. J. (2001). Blocking
histone deacetylation in Arabidopsis induces pleiotropic effects on
plant gene regulation and development. Proc. Natl. Acad. Sci.
USA 98,200
-205.
Tie, F., Furuyama, T., Prasad-Sinha, J., Jane, E. and Harte, P.
J. (2001). The Drosophila Polycomb group proteins
ESC and E(Z) are present in a complex containing the histone-binding protein
p55 and the histone deacetylase RPD3. Development
128,275
-286.
Tyler, J. K., Bulger, M., Kamakaka, R. T., Kobayashi, R. and Kadonaga, J. T. (1996). The p55 subunit of Drosophila chromatin assembly factor 1 is homologous to a histone deacetylase-associated protein. Mol. Cell. Biol. 16,6149 -6159.[Abstract]
Verbsky, M. L. and Richards, E. J. (2001). Chromatin remodeling in plants. Curr. Opin. Plant Biol. 4,494 -500.[CrossRef][Medline]
Verreault, A., Kaufman, P. D., Kobayashi, R. and Stillman, B. (1996). Nucleosome assembly by a complex of CAF-1 and acetylated histones H3/H4. Cell 87, 95-104.[Medline]
Verreault, A., Kaufman, P. D., Kobayashi, R. and Stillman, B. (1998). Nucleosomal DNA regulates the core-histone-binding subunit of the human Hat1 acetyltransferase. Curr. Biol. 8,96 -108.[Medline]
Wagner, D. and Meyerowitz, E. M. (2002). SPLAYED, a Novel SWI/SNF ATPase homolog, controls reproductive development in Arabidopsis. Curr. Biol. 12, 85-94.[CrossRef][Medline]
Western, T. L. and Haughn, G. W. (1999). BELL1 and AGAMOUS genes promote ovule identity in Arabidopsis thaliana. Plant J. 18,329 -336.[CrossRef][Medline]
Wu, K., Malik, K., Tian, L., Brown, D. and Miki, B. (2000). Functional analysis of a RPD3 histone deacetylase homologue in Arabidopsis thaliana. Plant. Mol. Biol. 44,167 -176.[CrossRef][Medline]
Yoshida, N., Yanai, Y., Chen, L., Kato, Y., Hiratsuka, J., Miwa,
T., Sung, Z. R. and Takahashi, S. (2001). EMBRYONIC FLOWER2,
a novel polycomb group protein homolog, mediates shoot development and
flowering in Arabidopsis. Plant Cell
13,2471
-2481.
Zhu, X., Demolis, N., Jacquet, M. and Michaeli, T. (2000). MSI1 suppresses hyperactive RAS via the cAMP-dependent protein kinase and independently of chromatin assembly factor-1. Curr. Genet. 38,60 -70.[CrossRef][Medline]