ABSTRACT
Chloroplast biogenesis has been well documented in higher plants, yet the complex methods used to regulate chloroplast activity under fluctuating environmental conditions are not well understood. In rice (Oryza sativa), the CYTOKININ-RESPONSIVE GATA TRANSCRIPTION FACTOR1 (Cga1) shows increased expression following light, nitrogen, and cytokinin treatments, while darkness and gibberellin reduce expression. Strong overexpression of Cga1 produces dark green, semidwarf plants with reduced tillering, whereas RNA interference knockdown results in reduced chlorophyll and increased tillering. Coexpression, microarray, and real-time expression analyses demonstrate a correlation between Cga1 expression and the expression of important nucleus-encoded, chloroplast-localized genes. Constitutive Cga1 overexpression increases both chloroplast biogenesis and starch production but also results in delayed senescence and reduced grain filling. Growing the transgenic lines under different nitrogen regimes indicates potential agricultural applications for Cga1, including manipulation of biomass, chlorophyll/chloroplast content, and harvest index. These results indicate a conserved mechanism by which Cga1 regulates chloroplast development in higher plants.
