Combinatory actions of CP29 phosphorylation by STN7 and stability regulate leaf age-dependent disassembly of photosynthetic complexes

Abstract

A predominant physiological change that occurs during leaf senescence is a decrease in photosynthetic efficiency. An optimal organization of photosynthesis complexes in plant leaves is critical for efficient photosynthesis. However, molecular mechanisms for regulating photosynthesis complexes during leaf senescence remain largely unknown. Here we tracked photosynthesis complexes alterations during leaf senescence in Arabidopsis thaliana. Grana stack is significantly thickened and photosynthesis complexes were disassembled in senescing leaves. Defects in STN7 and CP29 led to an altered chloroplast ultrastructure and a malformation of photosynthesis complex organization in stroma lamella. Both CP29 phosphorylation by STN7 and CP29 fragmentation are highly associated with the photosynthesis complex disassembly. In turn, CP29 functions as a molecular glue to facilitate protein complex formation leading phosphorylation cascade and to maintain photosynthetic efficiency during leaf senescence. These data suggest a novel molecular mechanism to modulate leaf senescence via CP29 phosphorylation and fragmentation, serving as an efficient strategy to control photosynthesis complexes.

An Argon-Ion-Induced Pale Green Mutant of Arabidopsis Exhibiting Rapid Disassembly of Mesophyll Chloroplast Grana

“…One of the most important findings of this study was that the pale leaf phenotype in Ar50-33-pg1 (and egy1-4 ) involved disassembly of the grana in mesophyll chloroplasts. Ultrastructural analyses of the chloroplast destruction processes during A. thaliana leaf aging have been performed using various systems [ 5 , 80 , 81 , 82 ], and can be summarized as follows: (i) chlorophyll degradation; (ii) onset of volume reduction in chloroplasts and thylakoids together with the production of plastoglobules; (iii) continued chloroplast and thylakoid volume reductions accompanied by chloroplast rounding, preferential destruction of stroma lamellae, granal thickening, and plastoglobule accumulation; and (iv) chloroplast number reduction and maximal growth or accumulation of plastoglobules at the expense of thylakoids, leading to the formation of gerontoplasts [ 7 ]. In this study, Ar50-33-pg1 and egy1-4 mesophyll chloroplasts followed similar chloroplast degeneration processes to those of leaf senescence, with the exception of the grana disassembly observed during chlorosis in the mutants ( Figure 7 , Figure 8 and Figure 9 ).…”

Structure of Dunaliella Photosystem II reveals conformational flexibility of stacked and unstacked supercomplexes

“…Thus far, PTMs were structurally seen in photosystems only as phosphorylated LHCII bound to PSI during state transition 50,51 . Although they were not identified in-situ, several phosphorylation sites were shown to exist in CP29 large stromal loop [52][53][54][55] . CP29 phosphorylation was suggested to be linked with various stress responses, photosynthetic protein degradation and state transition.…”

Function of Protein Kinases in Leaf Senescence of Plants

“…STN8 phosphorylates PSII (photosystem II) core proteins to modulate thylakoid ultrastructure and facilitates the repair of damaged PSII. STN7 and STN8 help to maintain optimal activity of the photosynthetic apparatus and have a crucial role in short-term acclimation and long-term responses ( Vainonen et al, 2005 ; Puthiyaveetil et al, 2012 ; Poudyal et al, 2020 ). Interestingly, both loss-of-function and overexpression of STN7 and STN8 result in early onset of senescence, suggesting that any perturbations of these two genes-regulated acclimation processes will induce early senescence in plants (Wang et al, 2015).…”