Light-intensity dependent expression of genes for light-harvesting chlorophyll-a/b proteins of photosystem II in Chlamydomonas reinhardtii

Abstract

We comprehensively characterized genes encoding light-harvesting chlorophyll a/b-binding (LHC) proteins of photosystem (PS) II in a unicellular green alga, Chlamydomonas reinhardtii, using the expressed sequence tag (EST) databases. C. reinhardtii ESTs related to PSII-LHC proteins were assigned to eight genes, including four new genes that were isolated and sequenced in this study. A sequence comparison revealed that C. reinhardtii has at least six genes corresponding to the major LHC (LHCII) proteins in higher plants, and two genes for the minor LHC proteins (CP29 and CP26). RT-PCR analysis showed that levels of these Lhc mRNAs changed in response to light intensity, and that the response was markedly affected by temperature and CO2 supply. Similar changes were observed for the multiple Lhc mRNAs. The results are interpreted to mean that the expression of Lhc genes is regulated in response to the imbalance between energy absorbed by the light-harvesting antenna systems and energy utilized for driving photosynthetic biochemical reactions. The regulation of Lhc gene expression must be involved in changing the antenna size of PSII during the acclimation to light intensity.