Common bean resistance to Xanthomonas is associated with upregulation of the salicylic acid pathway and downregulation of photosynthesis.

Abstract

Background: Common bacterial blight (CBB) caused by Xanthomonas phaseoli pv. phaseoli and Xanthomonas citri pv. fuscans is one of the major threats to common bean crops (Phaseolus vulgaris L.). Resistance to CBB is particularly complex as 26 quantitative resistance loci to CBB have been described so far. To date, transcriptomic studies after CBB infection have been very scarce and the molecular mechanisms underlying susceptibility or resistance are largely unknown. Results: We sequenced and annotated the genomes of two common bean genotypes being either resistant (BAT93) or susceptible (JaloEEP558) to CBB. Reciprocal BLASTp analysis led to a list of 20,787 homologs between these genotypes and the common bean reference genome (G19833), which provides a solid dataset for further comparative analyses. RNA-Seq after inoculation with X. phaseoli pv. phaseoli showed that the susceptible genotype initiated a more intense and diverse biological response than the resistant genotype. Resistance was linked to upregulation of the salicylic acid pathway and downregulation of photosynthesis and sugar metabolism, while susceptibility was linked to downregulation of resistance genes and upregulation of the ethylene pathway and of genes involved in cell wall modification. Conclusions: This study helps better understanding the mechanisms occurring during the early colonization phase of common bean by Xanthomonas and unveils new actors potentially important for resistance and susceptibility to CBB. We discuss the potential link between the pathways induced during bean colonization and genes induced by transcription activator-like effectors (TALEs), as illustrated in other Xanthomonas pathovars.

Regulatory Mechanisms of the Resistance to Common Bacterial Blight Revealed by Transcriptomic Analysis in Common Bean (Phaseolus vulgaris L.)

“…Due to the advantages of transcriptome analysis in the study of plant-pathogen interactions, multiple loci of resistance-related genes could be identified more easily. Xap has been studied by transcriptomics in rice ( Zhang et al, 2015 ; Fan et al, 2019 ; Bakade et al, 2021 ), tomato ( Shi and Panthee, 2020 ), pepper ( Gao et al, 2021 ), citrus ( Jalan et al, 2013 ; Ferrasa et al, 2020 ), sugarcane ( Ntambo et al, 2019 ), and common bean ( Foucher et al, 2020 ). Additionally, due to the advantages of WGNCA in gene function analysis, both differential expression analysis and WGNCA were used in the present study.…”

“…In previous reports, the transcriptomic response of the BAT93 and JaloEEP558 common bean genotypes was investigated after infection by Xanthomonas phaseoli pv. phaseoli , and resistance was found to be associated with the salicylic acid pathway and sugar metabolism; moreover, the genes involved were modified ( Foucher et al, 2020 ). In this study, two common bean genotypes, namely, the resistant genotype HR45 and the susceptible genotype Bilu, and one tepary bean genotype (PI 319443) were subjected to Illumina sequencing to analyse DEGs and resistance pathways in resistant and susceptible genotypes in response to infection by Xap .…”