Plastid and cytoplasmic origins of O-1(2)-mediated transcriptomic responses

The reactive oxygen species singlet oxygen, O-1(2), has an extremely short half-life, yet is intimately involved with stress signalling in the cell. We previously showed that the effects of O-1(2) on the transcriptome are highly correlated with 80S ribosomal arrest due to oxidation of guanosine residues in mRNA. Here, we show that dysregulation of chlorophyll biosynthesis in the flu mutant or through feeding by delta-aminolevulinic acid can lead to accumulation of photoactive chlorophyll intermediates in the cytoplasm, which generates O-1(2) upon exposure to light and causes the oxidation of RNA, eliciting O-1(2)-responsive genes. In contrast, transcriptomes derived from DCMU treatment, or the Ch1 mutant under moderate light conditions display commonalties with each other but do not induce O-1(2) gene signatures. Comparing O-1(2) related transcriptomes to an index transcriptome induced by cycloheximide inhibition enables distinction between O-1(2) of cytosolic or of plastid origin. These comparisons provide biological insight to cases of mutants or environmental conditions that produce O-1(2).