Abstract
BackgroundThe Root-Knot Nematode (RKN), Meloidogyne arenaria, significantly reduces peanut grain quality and yield worldwide. Whilst the cultivated species has low levels of resistance to RKN and other pests and diseases, peanut wild relatives (Arachis spp.) show rich genetic diversity and harbor high levels of resistance to many pathogens and environmental constraints. Comparative transcriptome analysis can be applied to identify candidate resistance genes.ResultsTranscriptome analysis during the early stages of RKN infection of two peanut wild relatives, the highly RKN resistant Arachis stenosperma and the moderately susceptible A. duranensis, revealed genes related to plant immunity with contrasting expression profiles. These included genes involved in hormone signaling and secondary metabolites production and also members of the NBS-LRR class of plant disease resistance (R) genes. From 345 NBS-LRRs identified in A.duranensis reference genome, 52 were differentially expressed between inoculated and control samples, with the majority occurring in physical clusters unevenly distributed on eight chromosomes with preferential tandem duplication. The majority of these NBS-LRR genes showed contrasting expression behaviour between A. duranensis and A. stenosperma, particularly at 6 days after nematode inoculation, coinciding with the onset of the Hypersensitive Response in the resistant species. The physical clustering of some of these NBS-LRR genes correlated with their expression patterns in the contrasting genotypes. Four NBS-LRR genes exclusively expressed in A. stenosperma are located within clusters on chromosome Aradu. A09, which harbors a QTL for RKN resistance, suggesting a functional role for their physical arrangement and their potential involvement in this defense response.ConclusionThe identification of functional novel R genes in wild Arachis species responsible for triggering effective defense cascades can contribute to the crop genetic improvement and enhance peanut resilience to RKN.
Highlights
The Root-Knot Nematode (RKN), Meloidogyne arenaria, significantly reduces peanut grain quality and yield worldwide
RNA-Seq data for both A. stenosperma and A. duranensis mapped to the A. duranensis reference genome On average, 97% of A. duranensis cleaned RNA-Seq reads from the three time-points studied could be mapped to the A. duranensis reference genome where they illuminated around 25,000 gene models (Table 1)
Over 95% of the A. stenosperma cleaned reads were cross-mapped to the A. duranensis reference genome where they illuminated over 22,000 gene models
Summary
The Root-Knot Nematode (RKN), Meloidogyne arenaria, significantly reduces peanut grain quality and yield worldwide. Whilst the cultivated species has low levels of resistance to RKN and other pests and diseases, peanut wild relatives (Arachis spp.) show rich genetic diversity and harbor high levels of resistance to many pathogens and environmental constraints. Whilst the cultivated species (Arachis hypogaea) has low levels of RKN resistance, peanut wild relatives (Arachis spp.) show rich genetic diversity harboring high levels of resistance to many pathogens and environmental constraints [2,3,4,5]. The wild species A. stenosperma harbors high levels of resistance against the peanut RKN M. arenaria and various foliar fungi [10,11,12,13,14]. In the moderately susceptible A. duranensis, the nematode reproduction occurs, albeit at lower levels and with a development delay when compared to the susceptible A. hypogaea [12]
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