EFFECTS OF IRON AND COPPER DEFICIENCY ON THE EXPRESSION OF MEMBERS OF THE LIGHT-HARVESTING FAMILY IN THE DIATOM THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE)1

The LI818 proteins and their Lhcx homologs in diatoms are a subgroup of the light-harvesting (LHC) antenna family, suspected of being involved in photoprotection and stress resistance. In this work, we report that the transcription of three LI818-like genes in Thalassiosira pseudonana Hasle et Heimdal (Lhcx1, Lhcx5, and Lhcx6) was down-regulated under iron or copper deprivation and when both trace metals were limiting, as was the case for Lhcf4, one of the standard light-harvesting genes. By contrast, the protein encoded by Lhcx1 was clearly up-regulated under iron limitation, suggesting that this gene is independently regulated at transcriptional and translational levels. In general, copper starvation had less effect on the expression of light-harvesting protein genes than iron deprivation, reflecting the different roles of iron and copper in photosynthetic function, that is, as an essential part of the electron transport chain versus as a cofactor for enzymes required to deal with the reactive oxygen species that result from inhibition of electron flow. Our results suggest that the Lhcx1 protein may be involved in stabilizing the photosynthetic apparatus when decreased nonphotochemical quenching (NPQ) results from Fe deficiency.