Retrograde signaling and photoprotection in a gun4 mutant of Chlamydomonas reinhardtii

We have carried out a transcriptional analysis in a gun4 mutant of the unicellular green alga Chlamydomonas reinhardtii as compared to the wild type, in dark-grown cells. GUN4 is a regulatory subunit of Mg-chelatase that is involved in the control of chlorophyll biosynthesis and coordinated nuclear gene expression. Previously, the involvement of GUN4 protein in coupling nuclear genome expression to chloroplast metabolism was demonstrated through norflurazon treatment that disrupts chloroplast function in Arabidopsis and LHCs for chlorophyll-binding subunits of photosystem antennae were the most responsive genes. The present transcript analysis has been instead performed under physiological condition, showing that, besides LHCs, 803 genes change their expression level in gun4 as compared to wild type. In Chlamydomonas the function of GUN4 becomes apparent under normal growth condition and implies a wide range genome-coupling effect.