Effect of activase level and isoform on the thermotolerance of photosynthesis in Arabidopsis

Abstract

Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) activation decreases under moderate heat stress. This decrease is caused by an impairment of activase function, which is exacerbated by faster rates of Rubisco deactivation at elevated temperatures. To determine if stromal oxidation causes inhibition of activase, transgenic Arabidopsis plants expressing suboptimal amounts of either the redox-regulated 46 kDa alpha- or non-redox regulated 43 kDa beta-isoform of activase were examined. Photosynthesis, as measured by gas exchange and chlorophyll fluorescence, and Rubisco activation were inhibited to a much greater extent by moderately high temperatures in the two transgenic lines expressing suboptimal levels of the individual isoforms of activase compared with wild-type plants or transgenic plants expressing levels of the beta-isoform sufficient for wild-type rates of photosynthesis. Net photosynthesis and Rubisco activation in transgenic plants expressing suboptimal amounts of the beta-isoform of activase from the Antarctic hairgrass were even more sensitive to inhibition by moderate heat stress than in the transgenic plants containing Arabidopsis activase. The results demonstrate that photosynthesis exhibits a similar sensitivity to inhibition by moderately high temperature in plants expressing either of the two different isoforms of activase. Thus, impairment of activase function under heat stress is not caused by oxidation of the redox-sensitive sulphydryls of the alpha-isoform of activase. Instead, the results are consistent with thermal denaturation of activase under moderate heat stress, the effects of which on Rubisco activation would be enhanced when activase levels are suboptimal for photosynthesis.

Drought stress and carbon assimilation in a warming climate: Reversible and irreversible impacts

“…Rubisco activase is a nuclear-encoded stromal protein present under two forms with different properties (Salvucci et al, 2006;Portis et al, 2008;Carmo-Silva and Salvucci, 2016).The longer redoxregulated α-isoform and the shorter β-isoform of rubisco activase are in some plants encoded in the same gene and are synthesized on two mRNAs produced from the same pre-mRNA by alternative splicing as illustrated in Fig. 3, process 2b (Werneke et al, 1989;Salvucci et al, 2003).…”

Extreme climatic events: impacts of drought and high temperature on physiological processes in agronomically important plants

“…The slightly larger form contains two cysteine residues in the C-terminal extension allowing a redox regulation via the thioredoxin system (Portis et al, 2008). The heat sensitivity of photosynthesis was found to be due to thermal denaturation of Rubisco activase and not to the oxidation of the cysteine residues in the larger form (Salvucci et al, 2006). The complex regulation of Rubisco activase (and as a consequence of Rubisco) and CO 2 fixation is not yet fully explored for all major crop plants and will remain a subject of research during the next years.…”

Genetic engineering for heat tolerance in plants

“…It should also be important to delineate various cellular events that may be affected by the aberrations caused in protein metabolism. Salvucci et al (2006) recently showed that thermal denaturation of rubisco activase is one of the key factors responsible for loss of rubisco activation under heat stress. According to Sage and Kubien (2007), limitations in electron transport and rubisco activase capacity should be more common, in the warmer, high CO 2 conditions expected by the end of the century.…”