The demands on agriculture of a growing human population are increasingly aggravated by our changing climate. Vernalization, the process by which prolonged exposure to cold temperatures initiates flowering competence, is a crucial regulator of plant development and hence crop productivity, and has thus been a key focus in agricultural developmental biology. However, the underlying molecular control of vernalization, and how the vernalization process works under variable temperatures, has remained unclear. Now, Laura Dixon and colleagues tackle these questions by investigating the response of different wheat varieties to variable temperatures. Out of a panel of 98 cultivars they identify one – named ‘Charger’ – with a delayed vegetative-to-reproductive transition in response to higher temperatures following standard vernalization. QTL analysis identifies the floral activator VRN1-A1 as a candidate locus controlling the phenotype, and distinct VRN-A1 haplotypes are shown to be regulated in distinct ways in response to warm temperatures. Expression of floral repressors is re-activated in response to high temperatures following standard vernalization, showing that vernalization is not simply defined by how long the plant experiences cold. Finally, analysis of leaf number, spikelet number and flowering time in a selection of wheat cultivars reveals diversity in the response to warm temperatures experienced during vernalization. This work therefore increases our understanding of the complexities of vernalization and provides clues as to how breeders might optimize vernalization in a warming world.
