RANDLE, CHRISTOPHER P.* and ANDREA D. WOLFE. Ohio State University, Department of Evolution Ecology and Organismal Biology, 1735 Neil Ave., Columbus OH 43210. - Molecular evolution of photosynthetic genes in holoparasites Harveya Hook. and Hyobanche L. (Orobanchaceae).
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