Down-regulation of the PSI-F subunit of photosystem I (PSI) in Arabidopsisthaliana - The PSI-F subunit is essential for photoautotrophic growth and contributes to antenna function

The PSI-F subunit of photosystem I is a transmembrane protein with a large lumenal domain, The role of PSI-F was investigated in Arabidopsis plants tr ansformed with an antisense construct of the psaF cDNA. Several plant lines with reduced amounts of the PSI-F subunit were generated. Many of the tran sgenic plants died, apparently because they were unable to survive without the PSI-F subunit. Plants with 5% of PSI-F were capable of photoautotrophic growth but were much smaller than wild-type plants. The plants suffered se verely under normal growth conditions but recovered somewhat in the dark in dicating chronic photoinhibition. Photosystem I lacking PSI-F was less stab le, and the stromal subunits PSI-C, PSI-D, and PSI-E were present in lower amounts than in wild type, The lack of PSI-F resulted in an inability of li ght-harvesting complex I-730 to transfer energy to the P700 reaction center . In thylakoids deficient in PSI-F, the steady state NADP reduction rate wa s only 10% of the wild-type levels indicating a lower efficiency in oxidati on of plastocyanin. Surprisingly, the lack of PSI-F also gave rise to disor ganization of the thylakoids, The strict arrangement in grana and stroma la mellae was lost, and instead a network of elongated and distorted grana was observed.