The reversal of red light-induced gene expression by far red light suggests the presence of a novel phytochrome-like molecule in the unicellular green alga Chlamydomonas reinhardtii.
- Amybeth Cohen, Professor of Biology, Director of MARC Scholars Program, California State University Fullerton
- Laura Arce, Part Time Faculty Member of Biology, Ph.D , California State University Fullerton
Photosynthesis is an essential mechanism employed in the eukaryotic, unicellular green alga Chlamydomonas reinhardtii. D1, a photosynthetic protein that is translated from the chloroplast-encoded psbA mRNA, is regulated by a class of nuclear-encoded RNA binding (RB) proteins (RB38, RB47 and RB60). The genes that encode these proteins (rb38, rb47 and rb60) have been shown to be light-regulated, and rb38 and rb60 are specifically regulated by red light. Red light regulation of these genes (Alizedah and Cohen, Plant Cell Physiol (2010) 51 (2): 312-322), as well as the nuclear psbO gene (encodes the photosynthetic Oxygen Evolution Enhancer 1 protein), suggests the presence of a phytochrome-like red light photoreceptor. Cellular responses induced by red light can be reversed by far-red light, a feature of phytochromes known as photoreversibility. This study aims to further characterize the red light response and to test the far-red light reversibility of rb and psbO gene expression. Dark-grown cells were shifted to red light, or red light followed by far red light, blue light, or dark. Reverse transcription polymerase chain reaction (RT-PCR) assays indicated that red light induces, and far-red light decreases, rb38 and psbO gene expression. The expression patterns for rb47, psbA and actin remained unchanged after a shift from the dark to any light treatment. The red light induction and far-red light reversibility of the rb38, rb60 and psbO genes supports the hypothesis that Chlamydomonas reinhardtii possesses a phytochrome-like photoreceptor. Further experiments, including bioinformatics analyses, are under way that which will allow for the identification of this photoreceptor and ultimately link the evolutionary progress of photoreceptors between photosynthetic bacteria and higher order plants.