Light-harvesting complex II kinase and chloroplast redox signaling

Abstract

Winter rye plants were grown under contrasting environmental conditions, or just transiently shifted to varying light/temperature regimes, to elucidate the acclimative processes of the light-harvesting complex II. Photosystem II (PSII) excitation pressure, reflecting the plastoquinone redox state, and the steady-state phosphorylation level of the thylakoid light-harvesting proteins (LHCII and CP29), together with accumulation of lhcb mRNA were monitored in vivo. Regulatory mechanisms of the phosphorylation of LHCII and CP29 were additionally explored in vitro. Obtained results allow us to make the following conclusions. (i) LHCII protein phosphorylation is a sensitive tool to monitor redox changes in chloroplasts. (ii) LHCII protein phosphorylation and lhcb mRNA accumulation are co-regulated, possibly via an activation state of the LHCII kinase. (iii) Excitation pressure of photosystem II (reduction state of the plastoquinone pool) is not directly involved in the regulation of lhcb mRNA accumulation. Instead, (iv) the redox status of the electron acceptors of photosystem I in the stromal compartment seems to be highly regulated and crucial for regulation of both the LHCII protein phosphorylation and lhcb gene expression in the nucleus. (v) Phosphorylation of CP29 is induced under plastoquinol-reducing conditions, and does not involve thiol redox-regulation