Regulation of flowering time in Japanese wild radish

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Flowering is the developmental turning point from vegetative to reproductive growth in the life cycle of many plants. The induction of flowering is the most important stage regarding reproductive strategy and the allocation of limited resources to seeds. Flowering time is determined by both developmental and external climatic cues, such as temperature and photoperiod, and is regulated by a complex hierarchical signalling network that integrates these stimuli.

For many Brassicaceae species, a period of cold is required for initiation of flowering. This phenomenon is termed vernalisation. Wild radish (Raphanus sativus) plants in northern and southern Japan exhibit obligate and facultative vernalization, respectively. In other words, northern populations require a cold period to flower whilst southern populations do not. However, vernalization hastens the flowering of both ecotypes, making them an excellent system for genetic studies of flowering-time variations.

In their new study published in AoBP, Han et al. conducted a detailed genetic analysis of flowering-time variation in response to cold and day length in wild radish collected from Hokkaido (northern population) and Okinawa (southern population) in Japan. The effects of cold exposure (with and without) and day length (long- and short-day) on flowering induction were evaluated using a controlled environment experiment with seeds collected from both populations.

The results of the study collectively offer a hint that accessions with obligate vernalization requirements might exhibit a higher sensitivity to prolonged cold exposure. On the other hand, for accessions with facultative vernalization requirements the photoperiod pathway predominates. The authors concluded that these mechanisms confer an optimal flowering time in natural populations, in response to their contrasting climate cues.