Expression Confers Flowering Competency and Is Negatively Correlated with Freezing Tolerance in .

Vernalization is an essential process by which many temperate plant species acquire competence for flowering. is a model plant for temperate grasses including many cool-season forage and turfgrasses and cereals. Grasses with spring growth habit do not require vernalization for flowering and are typically less winter hardy. Yet the connection between vernalization and freezing tolerance remain unclear. The diverse requirement of vernalization for flowering makes it an ideal choice for studying the relationship between vernalization and freezing tolerance. Here, we isolated and analyzed the spatial and temporal expression patterns of two vernalization related homologous genes, and in Bd21, a non-vernalization-requiring accession, and Bd29-1, an accession shown to be vernalization-requiring. We showed that expression of and is independent of vernalization in Bd21, but is vernalization dependent in Bd29-1. Moreover, vernalization-induced expression of appears to precede that of in Bd29-1. Bd21 RNAi knockdown mutants for conferred vernalization requirement for flowering, and reduced the expression of Both Bd29-1 and the RNAi mutants of Bd21 exhibited reduced freezing tolerance upon vernalization treatment. Cold-responsive genes , , , , and were all constitutively expressed at a high level in the RNAi mutants of Bd21. Taken together, our results suggest that expression of promotes flowering by upregulating , and gaining the competency for flowering reduces freezing tolerance in .