Light-Harvesting and Photoprotection in Diatoms: Identification and Expression of L818-Like Proteins

Abstract

The diatom Thalassiosira pseudonana has genes for at least 30 members of the Light- harvesting Complex (LHC) superfamily dispersed over a number of chromosomes but often found in pairs. Since diatoms do not have genes for PsbS, which is essential for non-photochemical quench- ing in plants, we are investigating the possibility that several proteins related to the stress-induced LI818 proteins of green algae could be taking the place of PsbS in responding to high light stress. The expression patterns of these “Lhcx” genes under different light intensities were assayed by real-time RT-PCR and compared with several “standard” Lhcf genes encoding the major fucox- anthin Chl a/c proteins. Lhcx1/2 was up-regulated 4–5 times after 1 h high light (HL), then dropped 30% in the next 5 h. Lhcx4 was also upregulated, although not as strongly, and Lhcx5 was unaf- fected. An antibody specific for the C-terminus of Lhcx1 identified it as a 22 kDa protein, which remained elevated after 6 h HL.