Abiotic stress remains one of the major challenges in managing and preventing crop loss. Photosystem II (PSII), being the most susceptible component of the photosynthetic machinery, has been studied in great detail over many years. However, much of the emphasis has been placed on intrinsic proteins, particularly with respect to their involvement in the repair of PSII-associated damage. PSII extrinsic proteins include PsbO, PsbP, PsbQ, and PsbR in higher plants, and these are required for oxygen evolution under physiological conditions. Changes in extrinsic protein expression have been reported to either drastically change PSII efficiency or change the PSII repair system. This review discusses the functional role of these proteins in plants and indicates potential areas of further study concerning these proteins.

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Developing efficient stress-tolerant crops through genetic engineering remains one of the major challenges for plant biologists. Approximately 20-40% genes of the known eukaryotic genomes, encode proteins of unknown function which lack currently defined motifs or domains. In a previous study, large-scale yeast functional screening approach in potato was used and 69 genes were reported to have enhanced hyperosmotic stress tolerance of yeast. Twelve out of 69 genes were found to have stress tolerance against multiple stresses. One of those 12 identified genes (StD200) encodes a protein of unknown function. In this study, we evaluated the tolerance against PEGinduced osmotic stress in transgenic Arabidopsis plants expressing putative abiotic stressassociated D200 gene. The D200 plants exhibited higher accumulation of chlorophyll and proline and reduced levels of oxidants compared to the wild-type (WT) control plants when subjected to PEG-induced osmotic stress conditions. Our quantitative Real-Time PCR results also suggested an increased accumulation of mRNA transcripts of genes encoding three major antioxidant enzymes in PEG-treated D200 plants compared to WT. Furthermore, improved photosynthetic parameters, F v / F m and performance index in PEG-treated D200 plants indicated that potato D200 gene is a potential candidate gene for developing stress-tolerant crops in future.

In this study, transgenic Arabidopsis lines expressing a potato gene (D43), encoding Glyceraldehyde 3phosphate dehydrogenase, were studied. The D43 plants exhibited improved morphological parameters and accumulation of photosynthetic pigments compared to wild-type (WT) plants under salinity stress conditions. In addition, the D43 transgenic plants showed significantly reduced electrolyte leakage, higher stomatal conductance, lower malondialdehyde (MDA) content, and higher proline content than the WT plants under salinity stress. The gene expression analysis showed that the D43 plants accumulated 1.7-fold, 2.2-fold, and 1.3-fold higher mRNA transcripts of genes encoding the antioxidant enzymes ascorbate peroxidase (APX), superoxide dismutase (SOD), and catalase (CAT), respectively under salt-stress conditions. Furthermore, they significantly altered the expression of seven major stress-responsive genes, which indicated that overexpression of the potato D43 gene gave salinity stress resistance to Arabidopsis. Chlorophyll-a fluorescence kinetics confirmed the efficient photon absorption, electron transport, and overall PSII efficiency that led to improved photosynthesis in the D43 plants subjected to NaCl-induced salinity stress. Overall, our findings have suggested that potato D43 is a potential candidate gene for developing salinity stress resistance in higher plants.