| LHCSRs: Novel players in NPQ in Chlamydomonas reinhardtii |
| Thuy B. Truong1,2, Graham Peers2, Dafna Elrad3, Arthur Grossman3, Marilyn Kobayashi1, William Inwood1, Sydney Kustu1, Giulia Bonente4, Roberto Bassi4, Tae K. Ahn5, Graham Fleming2,5, and Krishna K. Niyogi1,2 |
| 1) Dept. of Plant and Microbial Biol., Univ. of California, Berkeley, CA 94720 2) Physical Biosciences Division, Lawrence Berkeley Natl. Lab, Berkeley, CA 94720 3) Dept. of Plant Biol, Carnegie Institution, Stanford, CA 94305 4) Dipt. Scientiļ¬co e Tecnologico, Univ. di Verona, Italy 5) Dept. of Chemistry, Univ. of California, Berkeley, CA 94720 |
| Plants and algae need light to carry out photosynthesis, but too much light can be harmful to these organisms. Excess absorbed light leads to the production of reactive oxygen species that can cause photo-oxidative damage to pigments, proteins, and lipids in the thylakoid membranes. To minimize photoinhibition, the excess energy is dissipated as heat via non-photochemical quenching (NPQ) mechanisms. qE is a rapid component of NPQ that is turned on and off on a timescale of seconds to minutes. The roles of the xanthophyll cycle and the PsbS protein, a member of the light-harvesting complex (LHC) protein superfamily, have been well established in Arabidopsis qE. While xanthophyll cycle mutants in Chlamydomonas reinhardtii also have low qE, thus far no role for PsbS has been demonstrated in algae. To better understand NPQ in algae, Chlamydomonas mutants were generated. The npq4 mutant is defective in qE and is missing two LHCSR genes, which encode ancient members of the LHC superfamily. A second mutant lacking the third LHCSR gene also shows a defect in qE. The double mutant lacking all three LHCSRs has even lower qE compared to each of the single mutants. Recombinant LHCSRs bind pigments in vitro, and transient absorption spectroscopy experiments showed the formation of carotenoid radical cation species, which have been implicated in the mechanism of qE. These results suggest that LHCSRs act as quenchers of excited chlorophylls, and we hypothesize that they might also act as sensors of excess light. |
| e-mail address of presenting author: tbtruong@berkeley.edu |