Molecular and biophysical analysis of herbicide-resistant mutants of Chlamydomonas reinhardtii: structure-function relationship of the photosystem II D1 polypeptide.

Abstract

Plants and green algae can develop resistance to herbicides that block photosynthesis by competing with quinones in binding to the chloroplast photosystem II (PSII) D1 polypeptide. Because numerous herbicide-resistant mutants of Chlamydomonas reinhardtii with different patterns of resistance to such herbicides are readily isolated, this system provides a powerful tool for examining the interactions of herbicides and endogenous quinones with the photosynthetic membrane, and for studying the structure-function relationship of the D1 protein with respect to PSll electron transfer. Here we report the results of DNA sequence analysis of the D1 gene from four mutants not previously characterized at the molecular level, the correlation of changes in specific amino acid residues of the D1 protein with levels of resistance to the herbicides atrizine, diuron, and bromacil, and the kinetics of fluorescence decay for each mutant, which show that changes at two different amino acid residues dramatically slow PSll electron transfer. Our analyses, which identify a region of 57 amino acids of the D1 polypeptide involved in herbicide binding and which define a D1 binding niche for the second quinone acceptor, Qe of PSII, provide a strong basis of support for structural and functional models of the PSll reaction center.

Discovery of plastoquinones: a personal perspective

“…Evidence for quinones in the energy conversion systems of plants, animals, and microbes made the general concept of proton driven energy conversion possible (Wolstenholm and O'Connor 1961). The identification of the PQ binding site as also a site for herbicide action is of practical benefit for herbicide design (Erickson et al 1989). The discovery of PQB and PQC introduced new problems.…”

“…Mutants for the PQ-binding protein in PS II are known and recognized as also acting as the binding site for several herbicides. Which type of PQ can bind at these sites is unknown (see, e.g., Erickson et al 1989). …”

Reduced Turnover of the D1 Polypeptide and Photoactivation of Electron Transfer in Novel Herbicide Resistant Mutants of Synechocystis sp. PCC 6803

“…Fluorescence yield decay measurements on the second timescale revealed that the relaxation kinetics in the mutants have about a 1 s halftime, which is not affected by the presence of diuron (data not shown). Slower reoxidation of QA by Q, has been demonstrated before to be typical behaviour of PSI1 of some herbicide-resistance mutants (Erickson et al, 1989;Etienne et al, 1990;Ohad and Hirschberg, 1992). However, the very slow decay observed for the A263P and S264P mutants seems to indicate the almost complete block of the QA to Q, electron-transfer step, which is in an apparent contradiction with the ability to evolve oxygen by these mutants at about half of TC31 rates.…”

DCMU-resistance mutation confers resistance to high salt stress in the red microalgaPorphyridiumsp. (Rhodophyta)

“…Thus, a DCMU-resistant mutant might serve as a useful tool to study the impact of PS II modification on the response of photosynthetic organisms to an environmental stress. It has been reported that resistance to DCMU is often acquired by an alteration of the herbicidebinding site (D1 protein) on the thylakoid membranes, which results in a reduced affinity of the herbicide with the binding site (Galloway & Mets, 1984;Erickson et al, 1989;Galloway & Mets, 1989). DCMU-resistant mutants of higher plants and green algae were shown to involve single amino-acid substitutions in the D1 protein (Hirschberg & McIntosh, 1983;Hirschberg et al, 1987;Erickson et al, 1989;Mengistu et al, 2000Mengistu et al, , 2005.…”

“…It has been reported that resistance to DCMU is often acquired by an alteration of the herbicidebinding site (D1 protein) on the thylakoid membranes, which results in a reduced affinity of the herbicide with the binding site (Galloway & Mets, 1984;Erickson et al, 1989;Galloway & Mets, 1989). DCMU-resistant mutants of higher plants and green algae were shown to involve single amino-acid substitutions in the D1 protein (Hirschberg & McIntosh, 1983;Hirschberg et al, 1987;Erickson et al, 1989;Mengistu et al, 2000Mengistu et al, , 2005. Such mutants usually present additional pleiotropic effects, such as an increased sensitivity to strong illumination (Sundby et al, 1993;Alfonso et al, 1996), tolerance to irradiance (Singh & Singh, 1997), tolerance to heat stress (Alfonso et al, 2001) and tolerance to salt stress (Singh & Kshatriya, 2002).…”