HvVRN2 responds to daylength, whereas HvVRN1 is regulated by vernalization and developmental status

Two genetic loci control the vernalization response in winter cereals; VRN1, which encodes an AP1-like MADS-box transcription factor, and VRN2, which has been mapped to a chromosome region containing ZCCT zinc finger transcription factor genes. We examined whether daylength regulates expression of H nu VRN1 and H nu VRN2. In a vernalization-responsive winter barley ( Hordeum vulgare), expression of H nu VRN1 is regulated by vernalization and by development, but not by daylength. Daylength affected H nu VRN1 expression in only one of six vernalization-insensitive spring barleys examined and so cannot be a general feature of regulation of this gene. In contrast, daylength is the major determinant of expression levels of two ZCCT genes found at the barley VRN2 locus, H nu ZCCTa and H nu ZCCTb. In winter barley, high levels of H nu ZCCTa and H nu ZCCTb expression were detected only when plants were grown in long days. During vernalization in long-day conditions, H nu VRN1 is induced and expression of H nu ZCCTb is repressed. During vernalization under short days, induction of H nu VRN1 occurs without changes in H nu ZCCTa and H nu ZCCTb expression. Analysis of H nu ZCCTa and H nu ZCCTb expression levels in a doubled haploid population segregating for different vernalization and daylength requirements showed that H nu VRN1 genotype determines H nu ZCCTa and H nu ZCCTb expression levels. We conclude that the vernalization response is mediated through H nu VRN1, whereas H nu ZCCTa and H nu ZCCTb respond to daylength cues to repress flowering under long days in nonvernalized plants.