Flowering time regulation in perennial ryegrass

Abstract

Flowering in perennial ryegrass (Lolium perenne L.) is induced by a period of short days and low temperatures (vernalisation), followed by long-day photoperiod conditions. Genetic linkage mapping and association genetics studies have collectively identified 36 quantitative trait loci for flowering time which were distributed across all seven linkage groups of perennial ryegrass. Close to 40 genes (or putative orthologues/homologues of genes known from other species) for flowering time regulation have been identified, including central integrators and genes involved in four pathways (vernalisation, photoperiod, gibberellin, and autonomous). The structure and function of these predicted genes remains to be characterised. Although the photoperiod pathway is conserved in comparison to that of other temperate grasses, the vernalisation pathway appears to differ, due to absence of an orthologue of the cereal VRN2 gene. Although putative components from the autonomous pathway were identified, their target is unclear. No counterparts of genes from two other pathways (ageing and ambient temperature) have so far been reported. Given that c. 200 genes for flowering time regulation have been described in the model plant species Arabidopsis thaliana (L.) Heynh., additional genes may be identified from ryegrasses through comparative genomics approaches in the near future.