An Arabidopsis thaliana high Fo mutant had an impaired 33 kDa protein in oxygen evolving complex (OEC)

Abstract

We isolated Arabidopsis thaliana mutants by screening for high chlorophyll fluorescence. One of them, named LE18-30, has single recessive mutation and characterization of several photosynthetic proteins indicated LE18-30 accumulated less OEC33 protein than wild type. LE18-30 showed high Fo and also low quantum yield of PS2, resulting in much slower growth of LE18-30 than wild type in photoautotrophic condition. Further DNA sequence analysis of LE18-30 genes revealed that Gln159 of psbO gene coding OEC33 was replaced with stop codon by a single point mutation, whereas another OEC33-coding gene, psbO2, had no mutation. Detailed immuno-blot analysis with OEC33 antibodies also showed that wild type had two protein bands whereas LE18-30 had one band and lacked another protein band. These date suggested mutation in psbO was the cause of mutation and OEC33 translated from psbO2 gene was not sufficient for the photosynthesis. RT-PCR analysis showed that the quantity of psbO2 mRNA was much less than that of psbO, suggesting that small amount of psbO2 transcript limited the production of OEC33. To confirm our hypothesis, overexpression of psbO or psbO2 is conducted. And we are examining whether there is any difference between the expression patterns of psbO and psbO2.