TY - JOUR
T1 - Improved survival of very high light and oxidative stress is conferred by spontaneous gain-of-function mutations in Chlamydomonas
AU - Förster, Britta
AU - Osmond, C. Barry
AU - Pogson, Barry J.
PY - 2005/8/15
Y1 - 2005/8/15
N2 - Investigations into high light and oxidative stress in photosynthetic organisms have focussed primarily on genetic impairment of different photoprotective functions. There are few reports of "gain-of-function" mutations that provide enhanced resistance to high light and/or oxidative stress without reduced productivity. We have isolated at least four such very high light resistant (VHLR) mutations in the green alga, Chlamydomonas reinhardtii, that permit near maximal growth rates at light intensities lethal to wild type. This resistance is not due to an alteration in electron transport rate or quantity and functionality of the two photosystems that could have enhanced photochemical quenching. Nor is it due to reduced excitation pressure by downregulation of the light harvesting antennae or increased nonphotochemical quenching. In fact, photosynthetic activity is unaffected in more than 30 VHLR isolates. Instead, the basis of the VHLR phenotype is a combination of traits, which appears to be dominated by enhanced capacity to tolerate reactive oxygen species generated by excess light, methylviologen, rose bengal or hydrogen peroxide. This is further evidenced in lower levels of ROS after exposure to very high light in the VHLR-S9 mutant. Additionally, the VHLR phenotype is associated with increased zeaxanthin accumulation, maintenance of fast synthesis and degradation rates of the D1 protein, and sustained balanced electron flow into and out of PSI under very high light. We conclude that the VHLR mutations arose from a selection pressure that favors changes to the regulatory system(s) that coordinates several photoprotective processes amongst which repair of PSII and enhanced detoxification of reactive oxygen species play seminal roles.
AB - Investigations into high light and oxidative stress in photosynthetic organisms have focussed primarily on genetic impairment of different photoprotective functions. There are few reports of "gain-of-function" mutations that provide enhanced resistance to high light and/or oxidative stress without reduced productivity. We have isolated at least four such very high light resistant (VHLR) mutations in the green alga, Chlamydomonas reinhardtii, that permit near maximal growth rates at light intensities lethal to wild type. This resistance is not due to an alteration in electron transport rate or quantity and functionality of the two photosystems that could have enhanced photochemical quenching. Nor is it due to reduced excitation pressure by downregulation of the light harvesting antennae or increased nonphotochemical quenching. In fact, photosynthetic activity is unaffected in more than 30 VHLR isolates. Instead, the basis of the VHLR phenotype is a combination of traits, which appears to be dominated by enhanced capacity to tolerate reactive oxygen species generated by excess light, methylviologen, rose bengal or hydrogen peroxide. This is further evidenced in lower levels of ROS after exposure to very high light in the VHLR-S9 mutant. Additionally, the VHLR phenotype is associated with increased zeaxanthin accumulation, maintenance of fast synthesis and degradation rates of the D1 protein, and sustained balanced electron flow into and out of PSI under very high light. We conclude that the VHLR mutations arose from a selection pressure that favors changes to the regulatory system(s) that coordinates several photoprotective processes amongst which repair of PSII and enhanced detoxification of reactive oxygen species play seminal roles.
KW - Chlamydomonas
KW - High light resistance
KW - Photo-oxidative stress
KW - Photoprotection
KW - Photosynthesis
KW - Photosystem I and II
UR - http://www.scopus.com/inward/record.url?scp=23244432190&partnerID=8YFLogxK
U2 - 10.1016/j.bbabio.2005.05.012
DO - 10.1016/j.bbabio.2005.05.012
M3 - Article
SN - 0005-2728
VL - 1709
SP - 45
EP - 57
JO - Biochimica et Biophysica Acta - Bioenergetics
JF - Biochimica et Biophysica Acta - Bioenergetics
IS - 1
ER -