Antisense RNA for components associated with the oxygen-evolving complex and the Rieske iron/sulfur protein of the tobacco thylakoid membrane suppresses accumulation of mRNA, but not of protein.

Homologous cDNA clones of the nuclear-codes 23- and 33-kDa polypeptides of the oxygen-evolving system, as well as the Rieske iron/sulfur protein, were expressed in antisense or sense orientation under the control of the 35S RNA cauliflower mosaic virus promoter in transgenic tobacco (Nicotiana tabacum, L.) in order to modulate stationary concentrations of transcripts for studying relationships between transcript and protein levels. In all instances, in individuals that contained as little as 10% or less of the transcripts of untransformed plants, the corresponding protein levels were not notably altered. This indicated that the mRNA levels for components under study are not rate-limiting for protein accumulation and that severely reduced amounts of these transcripts still allow normal plant development. Overexpression of the 23-kDa polypeptide by the corresponding cDNA integrated in sense orientation resulted in both higher mRNA and protein levels without detectable enhancement of oxygen evolution. At least some of the excess protein was found in the soluble fraction and not associated with the photosystem-II reaction center. An attempt has been made to reconcile the varied responses obtained using these approaches with different expression patterns.