Characterization Of The Arabidopsis RINGLET Protein Reveals Its Function In The AtISWI Complex

The ATP-dependent remodeling complexes use the energy of ATPhydrolysis to change the status of chromatin and finally alternate geneexpressions through many ways like moving, assembling, replacing andejecting nucleosomes. The Imitation Switch (ISWI)-type chromatinremodeling factors have major and conserved functions in eukaryotes.Previous study reported that CHROMATIN-REMODELING PROTEIN11(CHR11) is an ATPase subunit of the ISWI-type chromatin remodelingcomplex in Arabidopsis. CHR11-RNAi plants exhibit multipledevelopmental defects: small size, limited cell expansion, defectivesporophytic cell and megagametophyte arrested at early phase. Inorder to reveal the natural functions of AtISWI, we characterized othermembers of the AtISWI complex: RINGLET1(RLT1) and its homologueRLT2.We show that CHR11can directly interact with RLT1/RLT2.Neitherthe rlt1nor rlt2single mutant displays any obvious developmentaldefects, while the rlt1rlt2double mutant displays many phenotypes:small size, early flowering and curly rosette leaves. We performed amicroarray analysis and a RT-PCR assay using wild-type and rlt1rlt2leaves, and identified genes such as SEPALLATA1(SEP1), SEP3andFRUITFULL (FUL) with increased expression levels in the double mutant.SEP1, SEP3and FUL are silenced by the Polycomb pathway through theH3K27me3modification. We demonstrate that RLT-ISWI may act withPolycomb pathway to repress SEP1, SEP3, and etc and regulate thephase change form vegetative growth to reproductive growth inArabidopsis.