Daniel P. Woods, Thomas S. Ream, Frédéric Bouché, Joohyun Lee, Nicholas Thrower, Curtis Wilkerson, and Richard M. Amasino

Significance

A key feature in the evolution of all vernalization systems is a cold-regulated component. In pooid grasses, up-regulation of the flowering promoter VERNALIZATION1 (VRN1) by prolonged cold is a key feature of vernalization, although little is known about the genes that repress VRN1 prior to cold exposure or activate it afterward. Here, we report the identification of REPRESSOR OF VERNALIZATION1 (RVR1), a repressor of VRN1 that is involved in creating a vernalization requirement in Brachypodium distachyon. RVR1 is present in all sequenced flowering plant genomes but is not found outside the plant kingdom. This report describes a role for the RVR1 class of genes in plants and an upstream component of the VRN1 regulatory system.

Abstract

A requirement for vernalization, the process by which prolonged cold exposure provides competence to flower, is an important adaptation to temperate climates that ensures flowering does not occur before the onset of winter. In temperate grasses, vernalization results in the up-regulation of VERNALIZATION1 (VRN1) to establish competence to flower; however, little is known about the mechanism underlying repression of VRN1 in the fall season, which is necessary to establish a vernalization requirement. Here, we report that a plant-specific gene containing a bromo-adjacent homology and transcriptional elongation factor S-II domain, which we named REPRESSOR OF VERNALIZATION1 (RVR1), represses VRN1 before vernalization in Brachypodium distachyon. That RVR1 is upstream of VRN1 is supported by the observations that VRN1 is precociously elevated in an rvr1 mutant, resulting in rapid flowering without cold exposure, and the rapid-flowering rvr1 phenotype is dependent on VRN1. The precocious VRN1 expression in rvr1 is associated with reduced levels of the repressive chromatin modification H3K27me3 at VRN1, which is similar to the reduced VRN1 H3K27me3 in vernalized plants. Furthermore, the transcriptome of vernalized wild-type plants overlaps with that of nonvernalized rvr1 plants, indicating loss of rvr1 is similar to the vernalized state at a molecular level. However, loss of rvr1 results in more differentially expressed genes than does vernalization, indicating that RVR1 may be involved in processes other than vernalization despite a lack of any obvious pleiotropy in the rvr1 mutant. This study provides an example of a role for this class of plant-specific genes.

See: http://www.pnas.org/content/114/25/6623.abstract.html?etoc

PNAS June 20 2017; vol.114; no.25: 6623–6628