Attenuation of cytosolic translation by RNA oxidation is involved in singlet oxygen‐mediated transcriptomic responses

Abstract

Singlet oxygen ( 1 O 2 ) production is associated with stress signalling. Here, using Arabidopsis as a model system, we study the effects of the accumulation of 8-hydroxyguanosine (8-oxoG), a major product of 1 O 2 -mediated RNA oxidation. We show that 8-oxoG can accumulate in vivo when 1 O 2 is produced in the cytoplasm.Conditions for such production include the application of RB in the light, dark-to-light transitions in the flu mutant, or subjecting plants to combined dehydration/light exposure. Transcriptomes of these treatments displayed a significant overlap with transcripts stimulated by the cytosolic 80S ribosomal translation inhibitors, cycloheximide and homoharringtonine. We demonstrate that 8-oxoG accumulation correlates with a decrease in RNA translatability, resulting in the rapid decrease of the levels of labile gene repressor elements such as IAA1 and JAZ1 in a proteasome-dependent manner. Indeed, genes regulated by the labile repressors of the jasmonic acid signalling pathway were induced by cycloheximide, RB or dehydration/light treatment independently of the hormone. The results suggest that 1 O 2 , by oxidizing RNA, attenuated cellular translatability and caused specific genes to be released from the repression of their cognate short half-life repressors. The findings here describe a novel means of gene regulation via the direct interaction of 1 O 2 with RNA.

Plastid and cytoplasmic origins of 1O2-mediated transcriptomic responses

“…Pchd accumulation in the flu mutant was previously shown to occur only in the chloroplast (op den Camp et al, 2003). However, Pchd fluorescence of dark-incubated flu mutant showed cytosolic accumulation that is confirmed here [Figure 2; (Koh et al, 2021)]. This finding may be due to the current advances in the sensitivity of confocal technology.…”

“…Transcriptomes for flu were obtained upon transfer of plants to light from the dark (GSE111286) and for Ch1 after dual application of light stress and cold ( Ramel et al., 2013 ). They were compared to CHX and RB transcriptomes ( Koh et al., 2021 ). Genes that were at least 2-fold upregulated, showed significant overlap of 49.2% (P = 2.9E-70) and 46.6% (P = 3.3E-118) with CHX and 39.9% (1.1E-106) and 29.1% (P = 1.2E-119) with RB, in flu and Ch1 respectively ( Figure 1A ).…”

“…When produced in the cytoplasm, 1 O 2 causes the oxidation of RNA and attenuation of cytoplasmic ribosomal translation. This results in decreased levels of short-lived repressor proteins, and stimulates the de-repression of the genes that they control ( Koh et al., 2021 ). From our analysis here and previously, we observed that many 1 O 2 signalling transcripts were highly correlated with CHX treatment, supporting the hypothesis of 1 O 2 promoting translational attenuation ( Koh et al., 2021 ).…”

“…Recently, we showed that cytosolic sources of 1 O 2 stimulated stress transcriptomes were correlated with cycloheximide (CHX) transcriptomes ( Koh et al., 2021 ). CHX is a potent and irreversible inhibitor of 80S ribosomal translation ( Schneider-Poetsch et al., 2010 ).…”

“…Thus, a wave of stress transcripts that are regulated by such proteins are freed from repression and accumulate as a 1 O 2 -specific stress signature. For example, jasmonic acid signalling genes that are repressed by short half-life JAZ repressors were stimulated via 1 O 2 mediated translational attenuation in the coi1 mutant, which is normally insensitive to JA ( Koh et al., 2021 ). It is important to note that the great majority of genes do not change their expression so that a degree of specificity is achieved by limiting the response to rapidly turning over transcriptional repressors or activators without reprogramming of the entire transcriptome.…”