Rice aleurone layer specific OsNF-YB1 regulates grain filling and endosperm development by interacti

Grain yield and quality of rice mainly depend on the grain filling and endosperm development. Here we report that a rice NUCLEAR FACTOR Y (NF-Y) transcription factor, OsNF-YB1, is specifically expressed in aleurone layer of developing endosperm and regulates grain filling and endosperm development. Knockdown of OsNF-YB1 expression by RNAi significantly retarded grain filling, leading to the small grains with chalky endosperm as well as altered starch quality. Whereas OsNF-YB1 shows the subcellular localization both in the cytosol and nucleus in roots, it specifically targets to the nucleus of aleurone layer cells, which is facilitated by interacting with OsNF-YC proteins preferentially expressed in aleurone layer. RNA sequencing analysis revealed that genes related to membrane transport and ATP biosynthesis are enriched in the down-regulated category in

OsNF-YB1 RNAi plants, which is consistent with the crucial role of OsNF-YB1 in rice grain filling and endosperm development. Identification of the genome-wide targets of OsNF-YB1 by ChIP sequencing showed that OsNF-YB1 directly regulates genes involved in the transport of nutrients such as sugar and amino acids. Interestingly, different from the binding sites reported for other NF-Y complexes, GCC-box, the binding motif of ERF transcription factors, is enriched in the binding peaks of OsNF-YB1. Indeed, further analyses confirm the interaction of OsERF#115 with OsNF-YB1 and OsERF#115 directly binds to GCC-box. It is proposed that OsNF-YB1 specifically regulate the transcription of downstream genes during rice endosperm development by forming protein complexes consisting of OsNF-YB1, OsNF-YC and ERF, providing informative insights into the molecular functional mechanisms of NF-Y factor.

Phenotypes of ptre1 mutant (left) and proposed model how PTRE1 regulates Aux/IAA protein degradation and auxin signaling (right).