AtFKBP16‐1, a chloroplast lumenal immunophilin, mediates response to photosynthetic stress by regulating PsaL stability

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Abstract
Arabidopsis contains 16 putative chloroplast lumen‐targeted immunophilins (IMMs). Proteomic analysis has enabled the subcellular localization of IMMs experimentally, but the exact biological and physiological roles of most luminal IMMs remain to be discovered. FK506‐binding protein (FKBP) 16‐1, one of the lumenal IMMs containing poorly conserved amino acid residues for peptidyl‐prolyl isomerase (PPIase) activity, was shown to play a possible role in chloroplast biogenesis in Arabidopsis, and was also found to interact with PsaL in wheat. In this study, further evidence is provided for the notion that Arabidopsis FKBP16‐1 (AtFKBP16‐1) is transcriptionally and post‐transcriptionally regulated by environmental stresses including high light (HL) intensity, and that overexpression of AtFKBP16‐1 plants exhibited increased photosynthetic stress tolerance. A blue native‐polyacrylamide gel electrophoresis/two‐dimensional (BN‐PAGE/2‐D) analysis revealed that the increase of AtFKBP16‐1 affected the levels of photosystem I (PSI)‐light harvesting complex I (LHCI) and PSI‐LHCI‐light harvesting complex II (LHCII) supercomplex, and consequently enhanced tolerance under conditions of HL stress. In addition, plants overexpressing AtFKBP16‐1 showed increased accumulation of PsaL protein and enhanced drought tolerance. Using a protease protection assay, AtFKBP16‐1 protein was found to have a role in PsaL stability. The AtPsaL levels also responded to abiotic stresses derived from drought, and from methyl viologen stresses in wild‐type plants. Taken together, these results suggest that AtFKBP16‐1 plays a role in the acclimation of plants under photosynthetic stress conditions, probably by regulating PsaL stability.

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