Functional and Molecular characterization of Flowering Locus C (FLC) homologs in Brachypodium distachyon ,,

Winter genotypes of temperate cereals require prolonged cold to transition from vegetative to reproductive development. This process, referred to as vernalization, has been extensively studied in Arabidopsis thaliana where it is regulated by a key flowering repressor called FLOWERING LOCUS C or FLC. By contrast, in cereals, vernalization is known to be regulated by the combined function of VERNALIZATION genes VRN1 and VRN2, which converge on flowering integrator FLOWERING LOCUS T (or VRN3 in cereals). These VRN genes are not orthologous to FLC. The function of recently identified grass FLC-like genes, has only been partially characterized. Here, we investigated the role of three FLC homologs (BdODDSOC1, BdODDSOC2 and BdMADS37) in the model grass Brachypodium distachyon. Our results revealed that all three FLC homologs are cold responsive under short days in different Brachypodium accessions. Moreover, in a winter accession, BdODDSOC2 responded to cold before BdVRN1. Functional characterization of FLC homologs by using transgenics shows that BdODDSOC2 indeed functions as a repressor of flowering because constitutive expression of BdODDSOC2 renders plants insensitive to vernalization and RNAi-mediated knockdown plants exhibit early flowering when grown without a vernalization treatment. However, we could not find any effect of vernalization on flowering time for BdODDSOC1 and BdMADS37 transgenic overexpression or RNAi plants. Furthermore, similar to FLC in Arabidopsis, we found that stable downregulation of BdODDSOC2 in response to vernalization is associated with the enrichment of H3K27me3 at BdODDSOC2 chromatin. Taken together, our study suggests that ODDSOC2 is not only phylogenetically related to FLC in eudicots, but also functions as a flowering repressor in the vernalization pathway of Brachypodium and likely other temperate grasses. These novel insights could prove useful in breeding efforts to refine the vernalization requirement of temperate cereals and adapt varieties to local climates, which is an important goal when these climates are rapidly changing.status: publishe