Abstract
To clarify the mechanism of the coordinate gene expression for assembly of photosynthetic apparatus, we studied plastic chloroplast differentiation in Arabidopsis roots. For root greening, we have clarified that light signaling mediated via HY5 is indispensable, and cytokinin and auxin signals oppositely regulate the coordinate expression for the root greening, which are mediated by other transcription factors. Recently, GARP transcription factor, Golden2-like (GLK), is identified to control genes involved in photosynthetic apparatus. Expression analysis of Arabidopsis isoforms, GLK1 and GLK2, in greening roots revealed the induction of GLK2, while GLK1 mRNA remained undetectable. Chlorophyll accumulation in double mutant glk1 glk2 was significantly lower than WT, while those in overexpressors GLK1OE and GLK2OE were approximately 6 and 3 fold higher than WT, respectively. These results suggest that the phytohormonal control of chloroplast differentiation is primarily mediated via GLK2 in Arabidopsis roots. As exogenous treatments of cytokinin or anti-auxin PCIB still enhanced chlorophyll accumulation in these lines, other factors may also be involved in this regulation.
