Molecular and global time-resolved analysis of a psbS gene dosage effect on pH- and xanthophyll cycle-dependent nonphotochemical quenching in photosystem II.
Photosynthetic light harvesting in plants is regulated by a pH- and xanthophyll-dependent nonphotochemical quenching process (qE) that dissipates excess absorbed light energy and requires the psbS gene product. An Arabidopsis thaliana mutant, npq4-1, lacks qE because of a deletion of the psbS gene, yet it exhibits a semidominant phenotype. Here it is shown that the semidominance is due to a psbS gene dosage effect. Diploid Arabidopsis plants containing two psbS gene copies (wild-type), one psbS gene (npq4-1/NPQ4 heterozygote), and no psbS gene (npq4-1/npq4-1 homozygote) were compared. Heterozygous plants had 56% of the wild-type psbS mRNA level, 58% of the wild-type PsbS protein level, and 60% of the wild-type level of qE. Global analysis of the chlorophyll a fluorescence lifetime distributions revealed three components in wild-type and heterozygous plants, but only a single long lifetime component in npq4-1. The short lifetime distribution associated with qE was inhibited by more than 40% in heterozygous plants compared with the wild type. Thus, the extent of qE measured as either the fractional intensities of the PSII chlorophyll a fluorescence lifetime distributions or steady state intensities was stoichiometrically related to the amount of PsbS protein.
Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720-3102, USA.
Xiao-Ping
XP
Li
Adam M
AM
Gilmore
Krishna K
KK
Niyogi
D029681:Arabidopsis Proteins; D005453:Fluorescence; D018628:Gene Dosage; D006863:Hydrogen-Ion Concentration; D008027:Light; D045342:Light-Harvesting Protein Complexes; D010777:Photochemistry; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000235:genetics*; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D012333:RNA, Messenger / Q000032:analysis; D020524:Thylakoids / Q000737:chemistry; D024341:Xanthophylls / Q000378:metabolism*
D029681:Arabidopsis Proteins; D045342:Light-Harvesting Protein Complexes; C489731:NPQ4 protein, Arabidopsis; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D012333:RNA, Messenger; D024341:Xanthophylls