Identification of theVERNALIZATION 4gene reveals the origin of spring growth habit in ancient wheats from South Asia

Abstract

Wheat varieties with a winter growth habit require long exposures to low temperatures (vernalization) to accelerate flowering. Natural variation in four vernalization genes regulating this requirement has favored wheat adaptation to different environments. The first three genes (VRN1–VRN3) have been cloned and characterized before. Here we show that the fourth gene,VRN-D4, originated by the insertion of a ∼290-kb region from chromosome arm 5AL into the proximal region of chromosome arm 5DS. The inserted 5AL region includes a copy ofVRN-A1that carries distinctive mutations in its coding and regulatory regions. Three lines of evidence confirmed that this gene isVRN-D4: it cosegregated withVRN-D4in a high-density mapping population; it was expressed earlier than otherVRN1genes in the absence of vernalization; and induced mutations in this gene resulted in delayed flowering.VRN-D4was found in most accessions of the ancient subspeciesTriticum aestivumssp.sphaerococcumfrom South Asia. This subspecies showed a significant reduction of genetic diversity and increased genetic differentiation in the centromeric region of chromosome 5D, suggesting thatVRN-D4likely contributed to local adaptation and was favored by positive selection. Three adjacent SNPs in a regulatory region of theVRN-D4first intron disrupt the binding ofGLYCINE-RICH RNA-BINDING PROTEIN 2(TaGRP2), a known repressor ofVRN1expression. The same SNPs were identified inVRN-A1alleles previously associated with reduced vernalization requirement. These alleles can be used to modulate vernalization requirements and to develop wheat varieties better adapted to different or changing environments.