NRPB3, the third largest subunit of RNA polymerase II, is essential for stomatal patterning and differentiation in Arabidopsis

Abstract

Stomata are highly specialized epidermal structures that control transpiration and gas exchange between plants and the environment. Signal networks underlying stomatal development have been previously uncovered, however, much less is known about how signals involved in stomatal development are transmitted to RNA polymerase II (Pol II), which plays a central role in the transcription of mRNA coding genes. Herein, we identified a partial loss-of-function mutation of the third largest subunit of nuclear DNA-dependent RNA polymerase II (NRPB3) that exhibited an increased number of stomatal lineage cells and paired stomata. Phenotypic and genetic analyses indicated that NRPB3 was not only required for correct stomatal patterning, but was also essential for stomatal differentiation. Protein-protein interaction assays showed that NRPB3 directly interacted with two basic-helix-loop-helix (bHLH) transcription factors, FAMA and INDUCER OF CBF EXPRESSION1 (ICE1), indicating that NRPB3 serves as an acceptor for signals from transcription factors involved in stomatal development. Our findings highlight the surprisingly conserved activating mechanisms mediated by the third largest subunit of Pol II in eukaryotes.