Transcription factor OsNF‐YC1 regulates grain size by coordinating the transcriptional activation of OsMADS1 in Oryza sativa L.

SUMMARY Grain weight, grain number per panicle, and the number of panicles are the three factors that determine rice ( Oryza sativa L.) yield. Of these, grain weight, which not only directly determines rice yield but also influences appearance and quality, is often considered the most important for rice production. Here, we describe OsNF‐YC1, a member of the NF‐Y transcription factor family that regulates rice grain size. OsNF‐YC1 knockout plants ( osnf‐yc1 ), obtained using CRISPR‐Cas9 technology, showed reduced grain weight due to reduced width and thickness, with no change in grain length, leading to a slenderer grain shape. Downregulation of OsNF‐YC1 using RNA interference resulted in similar grain phenotypes as osnf‐yc1 . OsNF‐YC1 affects grain formation by regulating both cell proliferation and cell expansion. OsNF‐YC1 localizes in both the nucleus and cytoplasm, has transcriptional activation activity at both the N‐terminus and C‐terminus, and is highly expressed in young panicles. OsNF‐YC1 interacts with OsMADS1 both in vivo and in vitro . Further analysis showed that the histone‐like structural CBFD‐NFYB‐HMF domain of OsNF‐YC1 conserved in the OsNF‐YC transcription factor family can directly interact with the MADS‐box domain of OsMADS1 to enhance its transcriptional activation activity. This interaction positively regulates the expression of OsMADS55, the direct downstream target of OsMADS1. Therefore, this paper reveals a potential grain size regulation pathway controlled by an OsNF‐YC1‐OsMADS1‐OsMADS55 module in rice.