Antisense Inhibition of the PsbX Protein Affects PSII Integrity in the Higher Plant Arabidopsis thaliana

PSII, the oxygen-evolving complex of photosynthetic organisms,contains an intriguingly large number of low molecular weightproteins. PsbX, one of these proteins, is ubiquitous in PSIIcomplexes of cyanobacteria and plants. In previous studies,deletion of the PsbX protein in cyanobacteria has not resultedin clear phenotypic changes. Here we report the constructionof an antisense (AS-PsbX) line in Arabidopsis thaliana with<10% of wild-type PsbX levels. AS-PsbX plants are capableof photoautotrophic growth, but biochemical, biophysical andimmunological evidence demonstrates that reduction of PsbX contentsleads to reduced levels of functional assembled PSII core complexes,while the light-harvesting antennae are not affected. In addition,levels of phosphorylation of the core proteins D1, D2 and CP43are severely reduced in the antisense plants relative to theirwild-type counterparts. We conclude that PsbX is important foraccumulation of functional PSII.