Submitted to: Journal of Experimental Botany
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/19/2008
Publication Date: 3/19/2008
Citation: Salvucci, M.E. 2008. Association of activase with chaperonin-60 beta: a possible mechanism for protecting photosynthesis during heat stress. Journal of Experimental Botany(59): 1923-1933. Interpretive Summary: In the process of photosynthesis, plants convert light into chemical energy. The energy produced by photosynthesis is then used to synthesize sugars and other foodstuffs. Heat stress inhibits photosynthesis, reducing the overall yield of the plant. Previous research from this research group identified an enzyme called Rubisco activase as the component of photosynthesis that is most sensitive to inhibition by heat. Rubisco activase is a regulatory enzyme that controls the activity of the major carbon dioxide-fixing enzyme in plants. In this manuscript, we present data that provides new insights into the biochemical mechanism that protects photosynthesis from inhibition during moderate heat stress. Specifically, we used transgenic plants with a modified form of activase to identify a specific protein that associates with activase and possible protects it from heat damage. The results provide new insights into our understanding of how photosynthesis responds to heat stress by showing that a specific protein seems to protect activase during episodes of high temperature. This information eventually can be used to make changes that improve the stability of Rubisco activase in order to improve the efficiency of photosynthesis under heat stress.
Technical Abstract: Previous studies have shown that inhibition of photosynthesis by moderate heat stress is a consequence of Rubisco deactivation, caused in part by the thermal instability of activase. This involvement of activase was confirmed in heat stress and recovery experiments using transgenic Arabidopsis plants. Compared with wild type plants, photosynthesis, 'PSII and Rubisco activation were less thermotolerant and recovered more slowly in transgenic Arabidopsis plants with reduced levels of activase. Immunoblots showed that nearly 60% of the activase was recovered in the insoluble fraction after heat stress in leaf extracts of transgenic but not wild type plants, evidence that deactivation of Rubisco was a consequence of thermal denaturation of activase. The transgenic Arabidopsis plants used in the study contained a modified form of activase that facilitated affinity capture of proteins that might interact with activase during heat stress. Affinity adsorption and elution of activase followed by sequence analysis and immunoblotting identified the beta-subunit of chaperonin 60 (cpn60beta, the chloroplast GroEL homolog, as a protein that co-eluted with activase in leaf extracts prepared from heat stressed, but not control plants. Non-denaturing gel electrophoresis showed that activase and cpn60 beta were associated in a high molecular mass complex. Immunoblot analysis established that the apparent association of cpn60beta with activase was dynamic, dependent on the duration and intensity of the heat stress and decreased following recovery. Taken together, these data suggest that cpn60beta plays a role in acclimating photosynthesis to heat stress, possibly by protecting activase from thermal denaturation.