Determination of the Key Resistance Gene Analogs Involved in Ascochyta rabiei Recognition in Chickpea

Abstract

Chickpea ( Cicer arietinum L.) is an important cool season food legume, however, its production is severely constrained by the foliar disease Ascochyta blight caused by the fungus Ascochyta rabiei (syn. Phoma rabiei ). Several disease management options have been developed to control the pathogen, including breeding for host plant resistance. However, the pathogen population is evolving to produce more aggressive isolates. For host resistance to be effective, the plant must quickly recognize the pathogen and instigate initial defense mechanisms, optimally at the point of contact. Given that the most resistant host genotypes display rapid pathogen recognition and response, the approach taken was to assess the type, speed and pattern of recognition via Resistance Gene Analog (RGA) transcription among resistant and susceptible cultivated chickpea varieties. RGAs are key factors in the recognition of plant pathogens and the signaling of inducible defenses. In this study, a suite of RGA loci were chosen for further investigation from both published literature and from newly mined homologous sequences within the National Center for Biotechnology Information (NCBI) database. Following their validation in the chickpea genome, 10 target RGAs were selected for differential expression analysis in response to A. rabiei infection. This was performed in a set of four chickpea varieties including two resistant cultivars (ICC3996 and PBA Seamer), one moderately resistant cultivar (PBA HatTrick) and one susceptible cultivar (Kyabra). Gene expression at each RGA locus was assessed via qPCR at 2, 6, and 24 h after A. rabiei inoculation with a previously characterized highly aggressive isolate. As a result, all loci were differentially transcribed in response to pathogen infection in at least one genotype and at least one time point after inoculation. Among these, the differential expression of four RGAs was significant and consistently increased in the most resistant genotype ICC3996 immediately following inoculation, when spore germination began and ahead of penetration into the plant’s epidermal tissues. Further in silico analyses indicated that the differentially transcribed RGAs function through ADP-binding within the pathogen recognition pathway. These represent clear targets for future functional validation and potential for selective resistance breeding for introgression into elite cultivars.

Differentiation of an Iranian resistance chickpea line to Ascochyta blight from a susceptible line using a functional SNP

“…It was concluded that the genes that do not have a consistent expression pattern could not be considered as the main resistance gene and it is important to determine the pattern of resistance (Leo et al 2016 ). Evaluation of candidate resistance gene analog (RGA) expression in resistant and sensitive plants even though resulted in the identification of four genes with up-regulation in the germination stage and initiation of penetration into the plant's epidermal tissues in the resistant genotype ICC3996 (Zhou et al 2019 ). Conversely, our results in the present study showed that none of these genes are present in the 100 Kb region AB4.1 (Li et al 2017 ).…”

“…In another study, ten RGA genes (Resistance Gene Analog) were selected based on the genomic data retrieved from the gene bank and their expression pattern was quantitatively investigated in resistant and susceptible chickpea plants at different hours after AB infection. The results showed that, the expression of four genes were significantly increased right after inoculation, during spore germination and the beginning of penetration into the plant’s epidermal tissues in the resistant genotype ICC3996 (Zhou et al 2019 ). Finally, they have concluded that, the decision to use these genes in breeding programs depends on evaluating their association with resistance to AB during complementary experiments.…”

Interactive Gene Expression Patterns of Susceptible and Resistant Lens ervoides Recombinant Inbred Lines and the Necrotroph Ascochyta lentis

“…Studies have shown that R-genes can enhance resistance against necrotrophs by inducing an appropriate level of ROS that promotes the production of antimicrobial compounds ( Quan et al, 2008 ; Zhu et al, 2017 ). So far, a variety of R-genes governing resistances against ascochyta blight have been reported in a L. culinaris accession and several chickpea accessions ( Coram and Pang, 2006 ; Khorramdelazad et al, 2019 ; Zhou et al, 2019 ). As the number of upregulated R-genes in LR-66-629 was higher than that in LR-66-570, we hypothesize that some of these R-genes upregulated in the former may contribute to its enhanced A. lentis resistance.…”

Sowing Date and Seeding Rate Affect Bioactive Compound Contents of Chickpea Grains

“…However, the effect of year, planting season, and variety indicate that the regulation of anti-nutrients in grain legumes might be extremely difficult. In addition, plant defense responses to pathogens (i.e., to A. rabiei ), through the synthesis of bioactive compounds with anti-nutritional effects involve a very specific metabolic event, multigenic governed by resistance-quantitative trait loci (R-QTL), where some metabolic pathways are still not well known [48].…”