Genome-wide analysis of Carica papaya reveals a small NBS resistance gene family
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The majority of plant disease resistance proteins identified to date belong to a limited number of structural classes, of which those containing nucleotide-binding site (NBS) motifs are the most common. This study provides a detailed analysis of the NBS-encoding genes of the fifth sequenced angiosperm, Carica papaya. Despite having a significantly larger genome than Arabidopsis thaliana, papaya has fewer NBS genes. Nevertheless, papaya maintains genes belonging to both Toll/interleukin-1 receptor (TIR) and non-TIR subclasses. Papaya’s NBS gene family shares most similarity with Vitis vinifera homologs, but seven non-TIR members with distinct motif sequence represent a novel subgroup. Transcript splice variants and adjacent genes encoding resistance-associated proteins may provide functional compensation for the apparent scarcity of NBS class resistance genes. Looking forward, the papaya NBS gene family is uniquely small in size but structurally diverse, making it suitable for functional studies aimed at a broader understanding of plant resistance genes.
KeywordsCarica papaya Resistance genes NBS-LRR genes TIR domain CC motif Alternative splicing
We thank Dr. Paul H. Moore for critical review of the manuscript and Mr. Ratnesh Singh and Dr. Ming-Li Wang at the Hawai’i Agriculture Research Center (HARC) for providing bioinformatics technical assistance. Funding for this project was provided by the United States Department of Agriculture (USDA), Cooperative State Research Education and Extension Service (CSREES), and Tropical and Subtropical Agriculture Research (T-STAR).
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