A novel proteinase, SNOWY COTYLEDON4, is required for photosynthetic acclimation to higher light intensities in Arabidopsis.
Excess light can have a negative impact on photosynthesis; thus, plants have evolved many different ways to adapt to different light conditions to both optimize energy use and avoid damage caused by excess light. Analysis of the Arabidopsis (Arabidopsis thaliana) mutant snowy cotyledon4 (sco4) revealed a mutation in a chloroplast-targeted protein that shares limited homology with CaaX-type endopeptidases. The SCO4 protein possesses an important function in photosynthesis and development, with point mutations rendering the seedlings and adult plants susceptible to photooxidative stress. The sco4 mutation impairs the acclimation of chloroplasts and their photosystems to excess light, evidenced in a reduction in photosystem I function, decreased linear electron transfer, yet increased nonphotochemical quenching. SCO4 is localized to the chloroplasts, which suggests the existence of an unreported type of protein modification within this organelle. Phylogenetic and yeast complementation analyses of SCO4-like proteins reveal that SCO4 is a member of an unknown group of higher plant-specific proteinases quite distinct from the well-described CaaX-type endopeptidases RAS Converting Enzyme1 (RCE1) and zinc metallopeptidase STE24 and lacks canonical CaaX activity. Therefore, we hypothesize that SCO4 is a novel endopeptidase required for critical protein modifications within chloroplasts, influencing the function of proteins involved in photosynthesis required for tolerance to excess light.
Australian Research Council Centre of Excellence in Plant Energy Biology , Australian National University Canberra, Acton, Australian Capital Territory 0200, Australia;
Verónica
V
Albrecht-Borth
Dominika
D
Kauss
Dayong
D
Fan
Yuanyuan
Y
Hu
Derek
D
Collinge
Shashikanth
S
Marri
Monique
M
Liebers
Klaus
K
Apel
Thomas
T
Pfannschmidt
Wah S
WS
Chow
Barry J
BJ
Pogson
D000064:Acclimatization / Q000528:radiation effects*; D020816:Amino Acid Motifs; D017360:Arabidopsis / Q000201:enzymology* / Q000502:physiology* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000378:metabolism*; D002736:Chloroplasts / Q000201:enzymology / Q000528:radiation effects; D017124:Conserved Sequence; D060146:Ecotype; D004579:Electron Transport / Q000528:radiation effects; D006861:Hydrogen Peroxide / Q000378:metabolism; D008027:Light; D008666:Metalloendopeptidases / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D010447:Peptide Hydrolases / Q000378:metabolism*; D010641:Phenotype; D038761:Photobleaching / Q000528:radiation effects; D010788:Photosynthesis / Q000528:radiation effects*; D045331:Photosystem I Protein Complex / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism; D010802:Phylogeny; D018515:Plant Leaves / Q000502:physiology / Q000528:radiation effects; D021381:Protein Transport / Q000528:radiation effects; D036226:Seedlings / Q000254:growth & development / Q000528:radiation effects; D013050:Spectrometry, Fluorescence; D013997:Time Factors
D029681:Arabidopsis Proteins; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D006861:Hydrogen Peroxide; D010447:Peptide Hydrolases; D008666:Metalloendopeptidases; C588163:SCO4 protein, Arabidopsis