Harveya Hook. (Orobanchaceae) is a genus of holoparasitic plants comprised of 25-40 species inhabiting southern Africa. Genes encoding photosynthetic proteins are expected to experience increased rates of mutation in holoparasites due to the relaxation of functional constraints on these genes. Hyobanche L., the sister genus of Harveya, has undergone rbcL pseudogene formation while species of Harveya have not. Two hypotheses may be invoked to explain the absence of an rbcL pseudogenes in Harveya. (a) The loss of Rubisco functionality has occurred via a different pathway in Harveya than rbcL pseudogene formation. (b) Rubisco retains function in Harveya, in facultative photosynthesis or an unknown, non-photosynthetic role. The gene encoding the small subunit of Rubisco, rbcS, has not been examined for loss of function in holoparasites. In this study, the evolution of Rubisco was examined by nucleotide sequencing of rbcL and rbcS, and detection of the RNA (RT-PCR) and protein products (by means of Western blot) of these genes in Hyobanche and Harveya. Structural motifs of the 3’ and 5’untranslated regions (UTRs) of rbcL may be important in promoting transcription. These were sequenced and analyzed for structural alterations which may prevent transcription of this gene.

Key words: gene expression, Harveya, holoparasitism, Hyobanche, Orobanchaceae, rbcL