Involvement of rice cryptochromes in de-etiolation responses and flowering

In order to elucidate the function of cryptochromes (cry) in rice, we have characterized all rice CRY genes, including OsCRY1a, OsCRY1b and OsCRY2. Our studies revealed that OsCRY1 genes were mainly expressed in the green plant tissue, while OsCRY2 gene expression was high in the coleoptile, flower and callus. Light treatment affected neither the expression of any of the OsCRY genes nor the stability of their transcripts. However, it was found that Oscry2 protein was negatively regulated by blue light. Moreover, the level of Oscry2 protein also decreased upon red light treatment, and this red light-dependent degradation was shown to be mediated by phytochrome B. Overexpression of OsCRY1 genes resulted in an increased responsiveness to blue light when measuring coleoptile growth inhibition. Moreover, growth of leaf sheaths and blades was also repressed more in OsCRY1 overexpressers than in wild type (WT) under blue light conditions. These results suggest that Oscry1s are responsible for regulating blue light-mediated de-etiolation in rice. In addition, OsCRY2 antisense transgenic rice flowered later than WT under both long-day and short-day conditions, indicating that Oscry2 is involved in the promotion of flowering time in rice.