RNA polymerase common subunit ZmRPABC5b is transcriptionally activated by Opaque2 and essential for endosperm development in maize

Maize (Zea mays) kernel size is an important factor determining grain yield; although numerous genes regulate kernel development, the roles of RNA polymerases in this process are largely unclear. Here, we characterized the defective kernel 701 (dek701) mutant that displays delayed endosperm development but normal vegetative growth and flowering transition, compared to its wild type. We cloned Dek701, which encoded ZmRPABC5b, a common subunit to RNA polymerases I, II and III. Loss-of-function mutation of Dek701 impaired the function of all three RNA polymerases and altered the transcription of genes related to RNA biosynthesis, phytohormone response and starch accumulation. Consistent with this observation, loss-of-function mutation of Dek701 affected cell proliferation and phytohormone homeostasis in maize endosperm. Dek701 was transcriptionally regulated in the endosperm by the transcription factor Opaque2 through binding to the GCN4 motif within the Dek701 promoter, which was subjected to strong artificial selection during maize domestication. Further investigation revealed that DEK701 interacts with the other common RNA polymerase subunit ZmRPABC2. The results of this study provide substantial insight into the Opaque2-ZmRPABC5b transcriptional regulatory network as a central hub for regulating endosperm development in maize.

Automated summary

Maize (Zea mays) kernel size is determined by numerous genes, and in this study, the role of RNA polymerases in kernel development was investigated. The Dek701 mutant exhibited delayed endosperm development but normal vegetative growth and flowering transition. The Dek701 gene encoded a common subunit to RNA polymerases I, II, and III, and its loss-of-function mutation affected the function of all three polymerases and altered gene transcription related to RNA biosynthesis, phytohormone response, and starch accumulation. Transcriptional regulation of Dek701 by the transcription factor Opaque2 was also observed, providing valuable insights into the regulatory network of endosperm development in maize.