Gaining cis-elements contributed to enhanced expression of C4 genes

C4 photosynthesis is derived from C3 photosynthesis. When related genes are compared, those involved in C4 photosynthesis tend to be more highly expressed. To understand this phenomenon, Singh et al. undertook a very impressive approach to look at transcriptional regulation of essentially all the photosynthetic genes in two members of the Brassicales, Arabidopsis thaliana (C3) and Cleome gynandra (C4). They focused on the first 24 hours of de-etiolation, when a dark-grown seeding is transferred to light and most of the photosynthetic genes are activated. They grouped the genes into expression clusters, and then further characterized them by looking at chromatin accessibility (DNase hypersensitivity), protein binding to the chromatin (Digital Genomic Footprinting), and the presence and occupancy of cis-regulatory elements. Although expression patterns of C3 and C4 genes were similar, the C4 genes showed enhanced expression levels. By undertaking such a comprehensive study, they were able to identify patterns that might not have been visible if only a small number of genes had been studied. There results highlight the accumulation of additional cis-regulatory elements, particularly G- and I-box elements, in the promoters of C4 genes as a key source of the elevated expression levels of these genes. (Summary by Mary Williams @PlantTeaching) Sci. Adv. 10.1126/sciadv.ade9756