Arabidopsis PEAPODs Function with LIKE HETEROCHROMATIN PROTEIN1 to Regulate Lateral Organ Growth

In higher plants, lateral organs are usually of determinate growth. It remains largely elusive how the determinate growth is achieved and maintained. Previous reports have shown that Arabidopsis PEAPOD (PPD) pro-teins suppress proliferation of dispersed meristematic cells partly through a TOPLESS corepressor complex. Here, we identified a new PPD-interacting partner, LIKE HETERO-CHROMATIN PROTEIN1 (LHP1), using the yeast two-hybrid system, and their interaction is mediated by the chromo shadow domain and the Jas domain in LHP1 and PPD2, respectively. Our genetic data demonstrate that the phe-notype of ppd2 lhp1 is more similar to lhp1 than to ppd2, indicating epistasis of lhp1 to ppd2. Microarray analysis re-veals that PPD2 and LHP1 can regulate expression of acommon set of genes directly or indirectly. Consistently, chromatin immunoprecipitation results confirm that PPD2 and LHP1 are coenriched at the promoter region of their targets such as D3-TYPE CYCLINS and HIGH MOBILITY GROUP A, which are upregulated in ppd2, lhp1 and ppd2 lhp1 mu-tants, and that PPDs mediate repressive histone 3 lysine-27 trimethylation at these loci. Taken together, our data pro-vide evidence that PPD and LHP1 form a corepressor complex that regulates lateral organ growth.