<i>OsMADS6</i> Controls Flower Development by Activating Rice <i>FACTOR OF DNA METHYLATION LIKE1</i>

Abstract

<i>OsMADS6</i>, an ancient <i>AGAMOUS-LIKE6</i> (<i>AGL6</i>)-like gene, has essential functions in specifying floral organ and meristem identity in rice (<i>Oryza sativa</i>). However, how <i>AGL6</i> genes control flower development remains largely unknown. In this study, we report that OsMADS6 directly targets <i>FACTOR OF DNA METHYLATION LIKE 1</i> (<i>OsFDML1</i>), a rice homolog of the <i>SUPPRESSOR OF GENE SILENCING3</i>-like gene <i>FACTOR OF DNA METHYLATION 1</i> (<i>FDM1</i>) from Arabidopsis (<i>Arabidopsis thaliana</i>). Arabidopsis <i>FDM1</i> is involved in RNA-directed DNA methylation and <i>OsFDML1</i> regulates flower development. The expression of <i>OsFDML1</i> overlaps with that of <i>OsMADS6</i> in the palea primordia and the ovule, and OsMADS6 directly promotes <i>OsFDML1</i> expression through binding to regions containing putative CArG motifs within the <i>OsFDML1</i> promoter during rice spikelet development. Consistent with the phenotypes of <i>osmads6</i> mutants, the <i>osfdml1</i> mutants showed floral defects, including altered palea identity with lemma-like shape containing no marginal region of palea, increased numbers of stigmas and fused carpels, and meristem indeterminacy. Moreover, transgenic plants overexpressing <i>OsFDML1</i> displayed floral defects, such as abnormal paleae. Phylogenetic analysis showed that <i>OsFDML1</i> homologs exist only in terrestrial plants. In addition, protein-protein interaction assays showed that OsFDML1 interacts with its close paralog OsFDML2, similar to the activity of OsFDML1 homologs in Arabidopsis. These results provide insight into how the ancient <i>AGL6</i> gene regulates floral development.