Arabidopsis MSI1 is required for epigenetic maintenance of reproductive development
2003
WD40 repeat proteins similar to yeast MSI1 are conserved in animals and
plants, in which they participate in complexes involved in chromatin
metabolism. Although MSI1-like proteins are well characterised biochemically,
their function in the development of multicellular eukaryotes is not well
understood. We constructed Arabidopsis plants in which the AtMSI1
protein level was altered. Strong ectopic expression of AtMSI1 produced no
visible altered phenotype, but reduction of AtMSI1 dramatically affected
development. The primary shoot apical meristem was unable to develop organs
after the transition to flowering. Flowers that developed on floral shoots
from axillary meristems experienced a progressive loss of floral morphology,
including a reduction in size of the petals and stamens and the development of
carpel-like sepals. Ovule development was disrupted in all flowers, resulting
in complete female sterility. Molecular analysis of the mutant plants revealed
that AtMSI1 is required to maintain the correct temporal and organ-specific
expression of homeotic genes, including AGAMOUS and
APETALA2 . In contrast, FAS1 and FAS2, which together with AtMSI1 form
the chromatin assembly complex CAF-1, are not required for repression of these
genes. Therefore, AtMSI1 has specific functions in addition to CAF-1-mediated
chromatin assembly. Efficient formation of heterochromatin, but not
methylation of centromeric DNA repeats, depends on AtMSI1 presence
demonstrating a key role of AtMSI1 in maintenance of chromatin structure.
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