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.

Silenced rice in both cytosolic ascorbate peroxidases displays pre-acclimation to cope with oxidative stress induced by 3-aminotriazole-inhibited catalase

“…Corroborating data previously reported (Bonifacio et al, 2011;Carvalho et al, 2014;Ribeiro et al, 2012;Rosa et al, 2010), the double silencing of cytosolic APX (APX1/2) by hairpin construction in rice was successfully obtained with a 90% decrease in both OsAPX1 and OsAPX2 transcripts compared with non-transformed (NT) plants (Fig. 1).…”

“…Regenerated seedlings were grown at 28 • C in MS medium with a photoperiod of 12 h and 150 mol m −2 s −1 of photosynthetic photon flux density (PPFD) in a growth chamber for seven days. In this study, we used the same silenced line at the F3 generation as previously utilized (Bonifacio et al, 2011;Carvalho et al, 2014;Ribeiro et al, 2012). These plants have exhibited similar cytosolic OsAPX1 and OsAPX2 transcript amounts and APX activity in the F1, F2 and F3 generations (Bonifacio et al, 2011).…”

“…Interestingly, single and double silencing of APX1 and APX2 trigger strong changes in redox metabolism, drastically altering the growth and development (Rosa et al, 2010). The up-expression of other peroxidases and photosynthetic proteins is able to compensate for deficiency in these enzymes (Bonifacio et al, 2011;Carvalho et al, 2014). The cytosolic APX knockdown in these plants is closely related to an increased H 2 O 2 concentration, which is able to trigger significant changes at the transcriptomics, proteomics and metabolic levels (Ribeiro et al, 2012).…”

Mitochondrial GPX1 silencing triggers differential photosynthesis impairment in response to salinity in rice plants

“…It is plausible to argue that this ROS could be involved in the growth regulation (Pnueli et al ) and perhaps mediating cross talking between organelles and other cellular compartments (Sewelam et al ). H 2 O 2 is a signaling molecule involved in photosynthesis modulation in rice (Bonifacio et al ; Carvalho et al ; Sousa et al ) and this process is one of the most important associated with plant growth. Thus, changes in the mitochondrial H 2 O 2 homeostasis associated with GPX abundance could trigger changes in chloroplasts involving a cross talk between these two organelles, with consequences on photosynthesis.…”

“…Despite several works using genetic approaches having clearly evidenced that downexpression of proteins encoded to cytosol and peroxisomes in rice are able to deeply alter photosynthesis, the metabolic and genetic mechanisms that control such changes are poorly known (Carvalho et al ; Sousa et al ). Particularly, the general effects caused by overexpression (or knockout) of some encoded mitochondrial proteins on photosynthesis are well characterized.…”