Ectopic expression of OsNF-YA8, an endosperm-specific nuclear factor Y transcription-factor gene, causes vegetative and reproductive development defects in rice

Abstract

Nuclear factor Y (NF-Y), a group of conserved transcription-factor complexes that consist of NF-YA, B, and C subunits, is essential for developmental regulation and for responses to environmental changes in eukaryotes. We previously found that some NF-Y genes, such as OsNF-YA8, were expressed specifically in the endosperm of rice. In the present study, overexpression of OsNF-YA8 in rice resulted in reduced plant height due to suppressed cell elongation in internodes. Gibberellin (GA) biosynthetic genes, including OsCPS1, OsGA20ox1, and OsGA20ox2, were down-regulated. OsNF-YA8 bound to the promoters of these genes to repress their expression. Endogenous GA content was decreased in OsNF-YA8 overexpressors, whose dwarf phenotype could be partially rescued by exogenous GA treatment. The findings suggested that ectopic expression of OsNF-YA8 causes defective GA biosynthesis in vegetative stage. Heading date in OsNF-YA8 overexpressors was delayed, especially under short-day conditions. OsNF-YA8 bound to the promoter of Heading Date 3a (Hd3a), the florigen gene in rice, to negatively regulate flowering. Either ectopic activation or knockout of OsNF-YA8 impaired seed development, as indicated by reduced seed size and increased grain chalkiness. These results suggest that ectopic expression of the endosperm-specific OsNF-YA8 in rice disrupts both vegetative and reproductive development.