Disruption of the Arabidopsis photosystem I gene psaE1 affects photosynthesis and impairs growth

The psae1-1 mutant of Arabidopsis was identified on the basis of a decrease in the effective quantum yield of photosystem II, among a collection of pl ants subjected to transposon tagging with the Enhancer element. The steady- state redox level and the rate of re-oxidation of P700 are significantly al tered in psae1-1 mutants. The responsible mutation was localised to psaE1, one of two Arabidopsis genes that encode subunit E of photosystem I. An add itional mutant allele, psae1-2, was identified by reverse genetics. In wild -type plants, the psaE1 transcript is expressed at a higher level than psaE 2 mRNA. In the mutants, however, the E1 transcript was barely detectable, a nd was expressed only in small groups of wild-type cells resulting from som atic reversions. As a consequence, the amount of PsaE protein present in th e mutant is significantly reduced. Concomitantly, the levels of other strom al photosystem I subunits (PsaC and PsaD) are also affected. Mutant plants showed a marked increase in light sensitivity and photoinhibition. Addition al effects of the psae1 mutation include light green pigmentation, an incre ase in chlorophyll fluorescence and a decrease of approximately 50% in grow th rate under greenhouse conditions.