The low molecular mass PsbW protein is involved in the stabilization of the dimeric photosystem II complex in Arabidopsis thaliana

Arabidopsis thaliana plants have been transformed with an antisense gene to the psbW of photosystem II (PSII). Eight transgenic lines containing low l evels of psbW mRNA have been obtained. Transgenic seedlings with low conten ts of PsbW protein (more than 96% reduced) were selected by Western blottin g and used for photosynthetic functional studies. There were no distinct di fferences in phenotype between the antisense and wild type plants during ve getative period under normal growth light intensities. However, a sucrose g radient separation of briefly solubilized thylakoid membranes revealed that no dimeric PSII supracomplex could be detected in the transgenic plants la cking the PsbW protein. Furthermore, analysis of isolated thylakoids demons trated that the oxygen-evolving rate in antisense plants decreased by 50% c ompared with the wild type, This was found to be due to up to 40% of D1 and D2 reaction center proteins of PSII disappearing in the transgenic plants. The absence of the PsbW protein also altered the contents of other PSII pr oteins to differing extents. These results show that in the absence of the PsbW protein, the stability of the dimeric PSII is diminished and consequen tly the total number of PSII complexes is greatly reduced. Thus the nuclear encoded PsbW protein may play a crucial role in the biogenesis and regulat ion of the photosynthetic apparatus.