NF ‐ YB 1‐ YC 12‐ bHLH 144 complex directly activates Wx to regulate grain quality in rice ( Oryza sativa L.)

Summary Identification of seed development regulatory genes is the key for the genetic improvement in rice grain quality. NF ‐Ys are the important transcription factors, but their roles in rice grain quality control and the underlying molecular mechanism remain largely unknown. Here, we report the functional characterization a rice NF ‐Y heterotrimer complex NF ‐ YB 1‐ YC 12‐ bHLH 144, which is formed by the binding of NF ‐ YB 1 to NF ‐ YC 12 and then bHLH 144 in a sequential order. Knock‐out of each of the complex genes resulted in alteration of grain qualities in all the mutants as well as reduced grain size in crnf‐yb1 and crnf‐yc12 . RNA ‐seq analysis identified 1496 genes that were commonly regulated by NF ‐ YB 1 and NF ‐ YC 12 , including the key granule‐bound starch synthase gene Wx . NF ‐ YC 12 and bHLH 144 maintain NF ‐ YB 1 stability from the degradation mediated by ubiquitin/26S proteasome, while NF ‐ YB 1 directly binds to the ‘G‐box’ domain of Wx promoter and activates Wx transcription, hence to regulate rice grain quality. Finally, we revealed a novel grain quality regulatory pathway controlled by NF ‐ YB 1‐ YC 12‐ bHLH 144 complex, which has great potential for rice genetic improvement.