FLOWERING LOCUS C orthologues with expression maxima in seeds are associated with an effect of vernalisation intensity on seed size Brassica napus

Abstract Warming during seed development can have negative impacts on seed size and crop yield across many species. Given the fact that there is substantial maternal control of seed size, it is also possible that temperature earlier in the growth cycle can affect crop physiology. Here, we analyse the response of a Brassica napus diversity set to variation in chilling temperature and duration. Our results show that increasing the chilling intensity positively affects seed size and weight, in addition to increasing the average number of seeds in each pod. Furthermore, we show that instead of silencing in response to vernalization, FLC C03a and FLC C09b genes show increasing expression during reproductive development that reaches a maximum in seeds, while retaining a clear effect of prior vernalization intensity on gene expression. We identify a weak allele of FLC C09b in Chinese semi-winter rapeseed varieties with an insertion in the first intron that is associated with a reduction in the sensitivity of seed size to variation in vernalization duration. We conclude that breeding for seed size traits may be important for mitigating the effects of low winter chilling on winter rapeseed yields.