PsbS is a high light inducible protein important for plant fitness

Abstract

One of the short-term high light protection mechanisms of plants is termed non-photochemical quenching (NPQ). PsbS, a member of the LHC family, has recently been shown to be essential for this mechanism. We have studied the regulation of PsbS, and also the performance of mutant plants lacking NPQ. In Arabidopsis thaliana, the expression of PsbS is upregulated after a high light shift, on RNA level as well as on protein level. PsbS is also upregulated after a shift to low temperature. We also measured the PsbS mRNA level in field-grown Populus. There was an immense day-to¿day variation in mRNA level that was highly correlated to meteorological data. Again, high light and low temperature induced the PsbS gene. Interestingly, we could show that the factors that mainly determine the transcript level is weather the afternoon before sample picking, rather than the same day. To determine the fitness of plants that lack NPQ, two Arabidopsis mutants (NPQ1, lacking Violaxanthin deepoxidase and NPQ4, lacking PsbS) were grown in the field. On average the mutants produced 40% less seeds than wild type, whereas the genotypes under constant conditions in the growth chamber produced the same the amount of seeds.