title: Cytosolic APX knockdown rice plants sustain photosynthesis by regulation of protein expression related to photochemistry, Calvin cycle and photorespiration.
abstract: The biochemical mechanisms underlying the involvement of cytosolic ascorbate peroxidases (cAPXs) in photosynthesis are still unknown. In this study, rice plants doubly silenced in these genes (APX1/2) were exposed to moderate light (ML) and high light (HL) to assess the role of cAPXs in photosynthetic efficiency. APX1/2 mutants that were exposed to ML overexpressed seven and five proteins involved in photochemical activity and photorespiration, respectively. These plants also increased the pheophytin and chlorophyll levels, but the amount of five proteins that are important for Calvin cycle did not change. These responses in mutants were associated with Rubisco carboxylation rate, photosystem II (PSII) activity and potential photosynthesis, which were similar to non-transformed plants. The upregulation of photochemical proteins may be part of a compensatory mechanism for APX1/2 deficiency but apparently the finer-control for photosynthesis efficiency is dependent on Calvin cycle proteins. Conversely, under HL the mutants employed a different strategy, triggering downregulation of proteins related to photochemical activity, Calvin cycle and decreasing the levels of photosynthetic pigments. These changes were associated to strong impairment in PSII activity and Rubisco carboxylation. The upregulation of some photorespiratory proteins was maintained under that stressful condition and this response may have contributed to photoprotection in rice plants deficient in cAPXs. The data reveal that the two cAPXs are not essential for photosynthesis in rice or, alternatively, the deficient plants are able to trigger compensatory mechanisms to photosynthetic acclimation under ML and HL conditions. These mechanisms involve differential regulation in protein expression related to photochemistry, Calvin cycle and photorespiration.
authors: Departamento de Bioquímica e Biologia Molecular, Universidade Federal do Ceará, Fortaleza, CE, Brazil.
authors: Fabrício E L
authors: FE
authors: Carvalho
authors: Carolina W
authors: CW
authors: Ribeiro
authors: Márcio O
authors: MO
authors: Martins
authors: Aurenivia
authors: A
authors: Bonifacio
authors: Charley C
authors: CC
authors: Staats
authors: Cláudia M B
authors: CM
authors: Andrade
authors: João V
authors: JV
authors: Cerqueira
authors: Márcia
authors: M
authors: Margis-Pinheiro
authors: Joaquim A G
authors: JA
authors: Silveira
mesh_terms: D000429:Alcohol Oxidoreductases / Q000235:genetics / Q000378:metabolism; D060387:Ascorbate Peroxidases / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D002374:Catalase / Q000235:genetics / Q000378:metabolism; D003600:Cytosol / Q000201:enzymology; D004307:Dose-Response Relationship, Radiation; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects; D005974:Glutamate-Ammonia Ligase / Q000235:genetics / Q000378:metabolism; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism; D009154:Mutation; D012275:Oryza / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D010101:Oxygen Consumption / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D010674:Pheophytins / Q000378:metabolism; D010788:Photosynthesis / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D045332:Photosystem II Protein Complex / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism; D013482:Superoxide Dismutase / Q000235:genetics / Q000378:metabolism
chemical_list: D007527:Isoenzymes; D045342:Light-Harvesting Protein Complexes; D010674:Pheophytins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D000429:Alcohol Oxidoreductases; C020821:glycollate oxidase; D060387:Ascorbate Peroxidases; D002374:Catalase; D013482:Superoxide Dismutase; D012273:Ribulose-Bisphosphate Carboxylase; C083818:glutamine synthetase 2; D005974:Glutamate-Ammonia Ligase