Chromosomal and phylogenetic context for conglutin genes in Arachis based on genomic sequence
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Comparative genomic and cDNA sequence analysis of ara h 2, a major peanut allergen, and a related conglutin ara h 6 were performed in Arachis hypogaea L. and its putative progenitors, Arachis duranensis and Arachis ipaensis. The complete identity between sequences encoding Ara h 2 isoforms demonstrated that these are homeologous genes and represent orthologs from diploid ancestors. Three copies of ara h 6 were identified in A. hypogaea, one of them located in the A-genome and the other two in the B-genome. Expression analysis showed higher levels of ara h 2 transcripts compared with ara h 6. Dual-labeled genomic in situ hybridization permitted identification of two subgenomes, each of which contained one pair of ara h 2-ara h 6 signals localized by fluorescence in situ hybridization. Characterization of genomic clones showed close genetic linkage between Ara h 2.02 and one copy of ara h 6 in the B-genome. The physical linkage may have arisen by tandem duplication and divergence of an ancestral gene. A gene duplication event specific to the B-genome progenitor has resulted in ara h 6 paralogs. These data provide further evidence for progenitor relationships and genomic organization of the conglutin gene family in the genus Arachis and could contribute to the development of a hypoallergenic peanut.
KeywordsAra h 2 Ara h 6 Conglutins Peanut allergens Homeologous genes Orthologous genes
This work was funded by a USDA-CSREES-administered special grant (00-34420-9178), the Georgia Peanut Commodity Commission and the Peanut Foundation. The authors thank Joann Conner for assistance with sequence analysis, Gunawati Gunawan for assistance with sequencing in house, Evelyn Morgan for assistance with embryo tissues, Shailendra Goel for assistance with image analysis and Anne Bell for her technical assistance. They also thank Bert Abbott, Clemson University, for providing peanut genomic and cDNA libraries and the Pratt Lab, UGA Athens Campus, for sequencing and bioinformatics support.
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