ANALYSIS OF EXPRESSION OF NBS-LRR RESISTANCE GENE ANALOGS IN MUSA ACUMINATE DURING COMPATIBLE AND INCOMPATIBLE INTERACTIONS WITH MYCOSPHAERELLA MUSICOLA

Sigatoka leaf spot, caused by the fungus Mycosphaerella musicola, significantly reduces leaf area and causes premature fruit ripening in banana. It is thus fundamentally important to develop genotypes resistant to fungal pathogens via crop improvement. In this context, transcriptional activity of NBS-LRR Resistance Gene Analogs (RGAs) was compared from whole plant leaf material from Musa acuminate ssp. burmannicoides ‘Calcutta-4’ (resistant) and Cavendish ‘Grande Naine’ (AAA, susceptible), uninoculated and inoculated in vivo with M. musicola pathogen conidiospores. Total RNA was extracted and purified using Concert^TM and cDNA prepared using the Kit SuperScript^TM II Reverse Transcriptase (Invitrogen). Twenty specific primer pairs for reverse transcriptase (RT) PCR were designed using Primer3plus and targeting NBS-LRR RGA contig exon sequences. Primers were also designed for the constitutively expressed M. acuminate actin gene (gi 151413782) and elongation factor (gi 66775523). RT-PCR results revealed examples of constitutive RGA gene expression in both compatible and incompatible interactions across the infection time course, as well as a complete absence of gene expression. Examples of RGAs showing similar expression patterns in compatible and incompatible interactions were also apparent, with susceptible and resistant cultivars, for example, showing low levels of expression in early infection stages and up-regulation in late stages. In contrast, another RGA displayed constitutive early expression in the resistant cultivar, strong down-regulation in the intermediate infection stage, and recovery to higher levels in the final stage of the examined infection time course. This project will contribute to the elucidation of disease resistance mechanisms in Musa. Candidate gene application via plant transformation or marker-assisted selection will benefit Musa breeding programs for the generation of resistant genotypes.