Expression of the nuclear-encoded rb60 gene that regulates the translation of the psbA mRNA in Chlamydomonas reinhardtii

The nuclear-encoded RB60, RB47, RB55 and RB38 proteins in Chlamydomonas reinhardtii form a complex that regulates the translation of the chloroplast-encoded psbA mRNA into D1, an essential photosystem II protein. Previous studies showed that rb60 mRNA accumulates to higher levels in light-grown Chlamydomonas reinhardtii cells than in dark-grown cells (R. Hawk and A. Cohen, unpublished). The aim of this study was to better understand the light-regulated expression of the rb60 gene. An increase in rb60 mRNA levels was seen with exposure of Chlamydomonas reinhardtii cells to white or blue light over a 60-minute period, but not to green or red light for the same period. Constitutive accumulation of the RB60 protein was observed under each of these four light conditions. The rb60 gene sequence was identified using the Joint Genome Institute Chlamydomonas reinhardtii version 1.0 database. Analysis of the rb60 promoter identified several putative light-inducible regulatory elements, including a blue-light responsive AAG-box. Future studies will elucidate whether one, or a combination of these regulatory elements, is involved in blue-light induced rb60 mRNA accumulation.