Arabidopsis MSI1 is required for epigenetic maintenance of reproductive development.
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.
Institute of Plant Sciences, Swiss Federal Institute of Technology, ETH Centre, CH-8092 Zürich, Switzerland.
Lars
L
Hennig
Patti
P
Taranto
Marcel
M
Walser
Nicole
N
Schönrock
Wilhelm
W
Gruissem
D017360:Arabidopsis / Q000196:embryology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D019295:Computational Biology; D035263:Flowering Tops / Q000254:growth & development; D018506:Gene Expression Regulation, Plant / Q000502:physiology; D006570:Heterochromatin / Q000502:physiology; D010802:Phylogeny; D018515:Plant Leaves / Q000254:growth & development; D034622:RNA Interference / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism
D029681:Arabidopsis Proteins; D006570:Heterochromatin; C475821:MSI1 protein, Arabidopsis; D012333:RNA, Messenger