NF-YC12 is a Key Multi-functional Regulator of Seed Storage Substance Accumulation in Rice

Starch and storage proteins, the primary storage substances of cereal endosperm, are a major source of food for humans. However, the transcriptional regulatory networks of the synthesis and accumulation of storage substances remain largely unknown. Here, we identified a rice endosperm-specific gene, NF-YC12, that encodes a putative nuclear factor-Y transcription factor subunit C. NF-YC12 is expressed in the aleurone layer and starchy endosperm during grain development. Knockout of NF-YC12 significantly decreased grain weight as well as altering starch and protein accumulation and starch granule formation. RNA-sequencing analysis revealed that in the nf-yc12 mutant genes related to starch biosynthesis and the metabolism of energy reserves were enriched in the down-regulated category. In addition, starch and protein contents in seeds differed between NF-YC12-overexpression lines and the wild-type. NF-YC12 was found to interact with NF-YB1. ChIP-qPCR and yeast one-hybrid assays showed that NF-YC12 regulated the rice sucrose transporter OsSUT1 in coordination with NF-YB1 in the aleurone layer. In addition, NF-YC12 was directly bound to the promoters of FLO6 (FLOURY ENDOSPERM6) and OsGS1;3 (glutamine synthetase1) in developing endosperm. This study demonstrates a transcriptional regulatory network involving NF-YC12, which coordinates multiple pathways to regulate endosperm development and the accumulation of storage substances in rice seeds.