Regulation of a maize HD–ZIP IV transcription factor by a non‐conventional RDR2‐dependent small RNA

Abstract

Small non-coding RNAs are versatile riboregulators that control gene expression at the transcriptional or post-transcriptional level, governing many facets of plant development. Here we present evidence for the existence of a 24 nt small RNA (named small1) that is complementary to the 3' UTR of OCL1 (Outer Cell Layer1), the founding member of the maize HD-ZIPIV gene family encoding plant-specific transcription factors that are mainly involved in epidermis differentiation and specialization. The biogenesis of small1 depends on DICER-like3 (DCL3), RNA-dependent RNA polymerase2 (RDR2) and RNA polymeraseIV, components that are usually required for RNA-dependent DNA-methylation. Unexpectedly, GFP sensor experiments in transient and stable transformation systems revealed that small1 may regulate its target at the post-transcriptional level, mainly through translational repression. This translational repression is attenuated in an rdr2 mutant background in which small1 does not accumulate. Our experiments further showed the possible involvement of a secondary stem-loop structure present in the 3' UTR of OCL1 for efficient target repression, suggesting the existence of several regulatory mechanisms affecting OCL1 mRNA stability and translation.