Conservation of the short-day vernalization flowering response pathway in temperate Pooideae grasses

The attainment of flowering competency to respond to inductive spring conditions is a critical step in the development of many temperate plants, enabling timely reproduction and maximizing fitness. Chilling and short-day (SD) 'vernalization' trigger flowering competency in grasses and other species, but the relative importance of each in the colonization of temperate habitats remains poorly understood. We found that SD vernalization is widespread in the Pooideae subfamily of temperate grasses, which includes many of the world's most important crops. Similarities in genes that transcriptionally respond to SDs suggest this trait evolved early in the clade's history as grasses transitioned from tropical to temperate regions. Among the candidate genes underlying a conserved SD vernalization response, the 14-3-3 gene GENERAL REGULATORY FACTOR 14h (GF14h) was found to be a flowering repressor that is downregulated under SD vernalization conditions. Expression analyses in mutant gf14h lines suggest that its repressive action relies on positive regulation of two downstream flowering repressors VERNALIZATION 2 (VRN2) and FLOWERING LOCUS T-LIKE 4 (FTL4), under LDs. In summary, we found that an SD vernalization response evolved early in the history of Pooideae grass diversification, likely through the co-option of an SD flowering regulon that includes GF14h, VRN2, and FTL4.