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Master of Science (MS)
Brodhagen, Marion (Marion L.)
Young, Jeff C. (Jeffery C.)
An extracellular arabinogalactan protein, PhPRP1, was identified from Petunia hybrida pistils on the basis of nucleotide sequence similarity with NaTTS from Nicotiana alata and TTS-1 from Nicotiana tabacum. PhPRP1 exhibits 83% and 81% nucleotide identity with NaTTS and TTS-1 cDNAs, respectively. The amino acid sequence deduced from the cDNA predicts a 27.4 kDa polypeptide backbone with a 25 amino acid signal sequence. Sequence alignments of PhPRP1 and the TTS proteins reveals two hypervariable regions, including a proline-rich domain with noncontiguous KPP repeats. A short, highly-conserved histidinerich domain separates the two hypervariable regions. The C-terminal segment of the protein shows significant sequence similarity to the Pollen Ole e 1 superfamily of arabinogalactan proteins, with perfect conservation of the six cysteine residues characteristic of the family. This multidomain architecture--especially the histidine-rich conserved domain and the proline-rich hypervariable region with KPP motifs--is a distinctive feature of TTS proteins and their orthologs in Petunia hybrida (PhPRP1) and Capsicum annuum (CaPRP1). An antibody specific to NaTTS detected PhPRP1, and purified PhPRP1 also reacted with β-glucosyl Yariv reagent, a dye that is diagnostic for arabinogalactans. BLAST searches identified sequences highly similar to PhPRP1 in expressed sequence tag (EST) libraries prepared from Petunia axillaris pistils and P. axillaris primary roots, which suggests that PhPRP1 is derived from the P. axillaris progenitor of P. hybrida, and that the PRP/TTS family of arabinogalactan proteins is not unique to pistil tissues. Phylogenetic analyses cluster the vegetative tissue ESTs with the pistil-expressed PRPs/TTS proteins at polytomies, indicating little differentiation among them. The gene geneology of PRPs/TTS proteins is mostly concordant with recent interpretations of the phylogeny of the Solanaceae based on concatenation of chloroplast and nuclear genes, with some differences in topology depending on the evolutionary models employed to construct the gene tree. As key mediators of pollenpistil interactions, PRP/TTS proteins may have an important role in generating reproductive barriers between sister species.
Arabinogalactan, Petunias--Reproduction, Petunias--Evolution, Natural selection, Solanaceae--Reproduction, Solanaceae--Evolution
Western Washington University
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Twomey, Megan, "Characterization of PhPRP1, an extracellular arabinogalactan protein from Petunia hybrida pistils" (2012). WWU Graduate School Collection. 236.