Journal Article

Rate heterogeneity in six protein-coding genes from the holoparasite <i>Balanophora</i> (Balanophoraceae) and other taxa of Santalales

Huei-Jiun Su and Jer-Ming Hu

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 110, issue 6, pages 1137-1147
Published in print November 2012 | ISSN: 0305-7364
Published online September 2012 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcs197
Rate heterogeneity in six protein-coding genes from the holoparasite Balanophora (Balanophoraceae) and other taxa of Santalales

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry

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Background and Aims

The holoparasitic flowering plant Balanophora displays extreme floral reduction and was previously found to have enormous rate acceleration in the nuclear 18S rDNA region. So far, it remains unclear whether non-ribosomal, protein-coding genes of Balanophora also evolve in an accelerated fashion and whether the genes with high substitution rates retain their functionality. To tackle these issues, six different genes were sequenced from two Balanophora species and their rate variation and expression patterns were examined.

Methods

Sequences including nuclear PI, euAP3, TM6, LFY and RPB2 and mitochondrial matR were determined from two Balanophora spp. and compared with selected hemiparasitic species of Santalales and autotrophic core eudicots. Gene expression was detected for the six protein-coding genes and the expression patterns of the three B-class genes (PI, AP3 and TM6) were further examined across different organs of B. laxiflora using RT-PCR.

Key Results

Balanophora mitochondrial matR is highly accelerated in both nonsynonymous (dN) and synonymous (dS) substitution rates, whereas the rate variation of nuclear genes LFY, PI, euAP3, TM6 and RPB2 are less dramatic. Significant dS increases were detected in Balanophora PI, TM6, RPB2 and dN accelerations in euAP3. All of the protein-coding genes are expressed in inflorescences, indicative of their functionality. PI is restrictively expressed in tepals, synandria and floral bracts, whereas AP3 and TM6 are widely expressed in both male and female inflorescences.

Conclusions

Despite the observation that rates of sequence evolution are generally higher in Balanophora than in hemiparasitic species of Santalales and autotrophic core eudicots, the five nuclear protein-coding genes are functional and are evolving at a much slower rate than 18S rDNA. The mechanism or mechanisms responsible for rapid sequence evolution and concomitant rate acceleration for 18S rDNA and matR are currently not well understood and require further study in Balanophora and other holoparasites.

Keywords: Balanophora; Balanophoraceae; B-class genes; LFY; RPB2; mitochondrial matR; substitution rate; phylogeny; Santalales; parasitic plants.

Journal Article.  7138 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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