Abstract
Chloroplasts are differentiated from proplastids in response to light and/or hormonal signals. However, the overall mechanisms have not been well documented. We have previously shown that OsGLK1, a GARP-type transcriptional regulator, is a key factor regulating chloroplast development [Nakamura et al. (2009) PCP 50: 1933-1949]. We also observed that the transcript level of OsGLK1 increased synchronously with the greening of wild-type calli after transfer to regeneration medium containing a low level of auxin and high concentration of cytokinin. So we carefully examined the relationship between auxin/cytokinin concentrations and the expression of OsGLK1, and found that auxin strongly repressed and cytokinin promoted the expression of OsGLK1. The transcriptional control may change OsGLK1 activity, and consequently affect chloroplast development. To uncover the mechanisms of the hormonal regulation of OsGLK1 expression, we are currently investigating whether and which factor(s), possibly involved in the cytokinin signal transduction, regulate the expression of OsGLK1.
