ISSN:
1399-3054
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
Notes:
Heterologous probes representing the entire tobacco chloroplast genome were used to investigate the degree of sequence conservation in the plastid DNA of the totally achlorophyllous plant Lathraea clandestina. Lathraea, a root parasite that grows in the soil, has retained a plastid genome in which the inverted repeat region (IR) is well conserved, with the exception of a short deletion in one of its extremities close to the large single copy region (LSC). Transcription of the 16S rRNA gene located in the IR was demonstrated, suggesting the functionality of the gene expression apparatus. Besides genes for ribosomal proteins (rps7 and rpl20) and for the plastid-encoded subunits of RNA polymerase (rpoA, rpoB, rpoC1 and rpoC2) were amplified by PCR. The single copy regions which contain most of the bioenergetic genes are more divergent than the inverted repeat regions with deleted or strongly altered sequences. This is particularly noticeable in the small one (SSC) which contains, in land plants studied so far, ndh genes for subunits of an NAD(P)H dehydrogenase. Despite some large deletions in the LSC, PCR experiments have shown that some photosynthetis genes, either functional (rbcL) or not (atpB–E) have been maintained. In addition heterologous hybridizations demonstrate that some genes (psaA, psaB, psbC–D) not amplified by PCR have been retained, at least partially. Because the psbA gene, despite having been amplified by PCR, did not map to any location on the Lathraea plastid genome, it is suspected that this sequence has been incorporated in another genome. From these findings we conclude that Lathraea plastid DNA is altered to a lesser extent than in Epifagus, a member of the Orobanchaceae, whilst being very different from Cuscuta reflexa whose plastid DNA (ptDNA) still contains all the photosynthetic genes found in autotrophic angiosperms. The maintenance of an intact rbcL gene might be the reason (or one of the reasons) why Lathraea has retained a plastid genome, even if the function of Rubisco in its amyloplasts remains unclear.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1399-3054.1996.tb00242.x
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