Role of HY5 in abscisic acid response in seeds and seedlings.

Seed dormancy offers plants an adaptive advantage that is crucial to their successful colonization of land. The decision to make the transition from a dormant seed to a photoautotrophic seedling is a result of a complex interaction of internal hormonal signals and external stimuli such as water, temperature and light. We recently showed that HY5, a well-characterized component in the light signaling pathway, also mediates abscisic acid (ABA) response during seed germination, early seedling growth and root development in Arabidopsis. We proposed that HY5 regulates these ABA responses partly by directly activating the transcription factor gene ABI5. By analyzing the premature germination of hy5 and abi5 single and double mutants, here we demonstrated that HY5 also positively controls seed maturation and dormancy, likely through direct activation of the ABI5 gene. The contrasting role of light regulation of seed development and germination may be important for the adaptation of plants to the environment.