Transcriptional control of vitamin C defective 2 and tocopherol cyclase genes by light and plastid-derived signals: The partial involvement of GENOMES UNCOUPLED 1

Previous findings have suggested that light and plastid-derived signals are involved in the regulation of biosynthetic pathways for l-ascorbic acid (AsA) and tocopherols (Toc). Photosynthetic electron transport (PET) activity, plastid gene expression (PGE), and the tetrapyrrole metabolism have been identified as signals that regulate nuclear gene expression through the GENOMES UNCOUPLED 1 (GUN1) protein. Here, we examined the effects of disrupting GUN1 on these pathways. The expression of vitamin C defective 2 (VTC2) and tocopherol cyclase (TC) genes, which encode key enzymes in the AsA and Toc biosynthetic pathways, respectively, was affected by illumination and darkness in parallel with the levels of both these antioxidants. However, the GUN1 disruption had no effect on these biosynthetic pathways under light-dark conditions. All treatments that inhibited PET, PGE, and the tetrapyrrole metabolism interrupted both biosynthetic pathways; however, this was partially mitigated by the GUN1 disruption. The expression patterns of VTC2 and TC reflected the levels of both antioxidants under most of the conditions examined. Our results suggest that the transcriptional control of VTC2 and TC by light and plastid-derived signals is important for the regulation of the biosynthetic pathways, and that GUN1 is at least partially involved in the plastid-derived signals-dependent regulation.