Abstract
Chlorophylls and their derivatives have a photooxidative activity under the light. Thus, in higher plants, chlorophyll biosynthesis is properly regulated at several biological steps such as transcription, translation and enzyme activation. Previous study in Arabidopsis showed that chlorophyll biosynthesis is strictly regulated at the transcriptional levels in response to light and growth conditions. To unravel the regulatory mechanism for chlorophyll biosynthetic genes, we focused on the chlorophyll accumulation in Arabidopsis roots. We found that cytokinin plays an important role in root greening. By contrast, auxin signals were indicated to have a negative effect on chlorophyll accumulation in the root. Transcriptome analysis showed that these hormonal signals are involved in the regulation of co-expression of chlorophyll biosynthetic genes. These hormonal effects on root greening were, however, completely abolished in hy5 mutant, suggesting that HY5 is a point of convergence between light and cytokinin/auxin signaling pathways in the root.
