Light Stress Acclimation and ROS Signal Transduction

 

Except for the npq1lor1 double mutant, most of our npq and antioxidant-deficient mutants of Chlamydomonas and Arabidopsis are able to acclimate to high light over a period of several days. Thus, it is apparent that other photoprotective processes are able to compensate for the lack of NPQ and/or specific antioxidants. We are taking several approaches to identify these other photoprotective processes.

One approach is to characterize and compare morphological, physiological, biochemical, and molecular traits of the mutants and the wild-type after acclimation to high light. These experiments include measurements of cell size, leaf anatomy, photosynthetic electron transport, mRNA expression analysis, chloroplast proteomics, and metabolite profiling. Preliminary results suggest a compensatory increase in levels of other antioxidants in some mutants.

In a genetic approach to uncover compensating mechanisms of light stress acclimation, we are constructing double (and triple) mutants that impair multiple known photoprotective processes. By screening for new second-site mutations that enhance the light sensitivity of a single mutant, we hope to identify previously unrecognized photoprotective mechanisms.

Long-term acclimation to high light is known to involve increases in antioxidants and decreases in light-harvesting antenna size that are likely due to changes in gene expression. For example, several green algal species exhibit massive accumulation of zeaxanthin and lutein under conditions of light stress, so we are using Chlamydomonas as a model green alga to identify genes that are involved in this process. We also hope to dissect the pathways responsible for light stress perception and signal transduction by screening for mutants that affect expression of a high-light-responsive promoter. In addition, because of the close association between light stress and oxidative stress, we are exploring the mechanisms of acclimation to ROS and the possible roles of ROS in signaling.

 

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