Effect of ambient temperature fluctuation on the timing of the transition to the generative stage in cauliflower

Cauliflower (Brassica oleracea ssp. botrytis) is an important vegetable that is grown worldwide from the tropics to temperate zones. The harvested product is the curd, which consists of arrested inflorescence meristems. The switch from vegetative development to curd formation in cauliflower, referred to as the generative switch, is strongly temperature responsive in the majority of varieties. We aimed at measuring the delay in timing of the generative switch by high ambient temperature, and how temperature affects the expression of genes with a potential role in timing of this switch. A seven day increase of six degrees in day and night temperature during vegetative development, results in a substantial delay of the generative switch and increased variation in timing of this switch in sensitive cultivars only. The expression level of the Cauliflower FRUITFULL-like gene BoFULc increased significantly at the generative switch and therefore can be used as marker for this developmental phase change. The expression profiles of the majority of the other investigated cauliflower flowering time genes resembled the expression behaviour of their homologous genes in the model plant Arabidopsis thaliana during the vegetative stage and flowering induction. An exception was the expression of two FLC paralogues BoFLC-1 and BoFLC-3, which showed opposite expression profiles of which the pattern of BoFLC-1 resembles the pattern expected based on Arabidopsis FLC. This interesting observation suggests different roles for these two FLC paralogs in regulation of the timing of the generative switch in cauliflower. Unexpectedly, high temperatures did not delay timing of expression of the majority of investigated genes in meristems and leaves of sensitive cultivars that were delayed in the switch to the generative stage. However, expression of a few potential flowering-time genes was affected by the high temperature treatment in a sensitive cultivar, making them potential candidates to be causal for the observed delay in generative switch.