Expression Analysis of R Gene-Mediated Defense Response Genes Identified in Leaf Transcriptome Sequences of Musa acuminata During Interaction with Mycosphaerella musicola

Bananas (Musa spp.) are cultivated across many tropical and subtropical environments, contributing to poverty alleviation and global food security. This study describes expression analysis of resistance (R) gene-mediated defense response genes from previously developed 454 transcriptome data in Musa acuminata during compatible and incompatible reactions with the fungal pathogen Mycosphaerella musicola, causal organism of Sigatoka leaf spot disease. A total of 846,762 high quality 454 sequence reads from disease resistance-contrasting M. acuminata genotypes Calcutta 4 and Cavendish Grande Naine were mapped against complete BAC clone sequences for each genotype. A total of 16 read assemblies were compiled, mapping to exon or UTR regions in R gene-like sequences from the classes LRR receptor-like serine/threonine-protein kinase, nucleotide-binding leucine-rich-repeat protein and serine/threonine protein kinase. A further 17 assemblies mapped to defense response genes such as glutathione peroxidase.  Primers were designed to exon and UTR regions using Primer3Plus, and verified for specificity against BAC sequences and 454 transcriptome data through electronic PCR using Emboss Primersearch. Validation of differential gene expression via qRT-PCR has confirmed expression in plant leaf tissues during this host-pathogen interaction.  Further transcriptome data mapping to the reference whole genome sequence for M. acuminata (DH Pahang) is ongoing. Candidate resistance gene discovery and expression analysis will contribute to disease-management based upon genetic improvement in banana, via both plant transformation and marker assisted breeding.