Fig. 7: Model of the chloroplast 1O2-induced retrograde signalling depending on the metabolites content.
Lack of a functional Mg-chelatase (MgCh) leads to accumulation of protoporphyrin IX (Proto), which in light generates 1O2. Absence of TSPP1 results in accumulation of trehalose 6-phosphate (Tre6P). In plants, Tre6P has an inhibitory effect on SnRK145,69,70, while altered SnRKs activity is also involved in stress responses in C. reinhardtii75,76,77,78. Blocked SnRK1 signalling pathway leads to the inadequate transcriptomic response to stress and disturbed metabolites content. Selected metabolites with altered content in gunSOS1 relative to sigRep are shown, increased in blue, decreased in red. Exogenous application of fumarate, 2-oxoglutarate, and myo-inositol always had an inhibitory effect on 1O2-signalling in sigRep, while no change was observed in gunSOS1 and WT, relative to their respective non-treated controls. Application of mannose 6-phosphate and glucose 6-phosphate at 20 and 50 μM each increased the expression of GPX5 in sigRep, but no change in GPX5 mRNA was observed in gunSOS1. Exogenous application of aconitate promoted expression of PSBP2, MBS, and SAK1, and consequently also GPX5, which ultimately indicated the rescue of 1O2-signalling in gunSOS1. Intracellular localisation of TSPP1, SnRK1, and PSBP2 depicted in the Figure has not been determined experimentally and has only an illustrative character. Mitochondria are marked by an asterisk.
