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Plant responses underlying nonhost resistance of Citrus limon against Xanthomonas campestris pv. campestris.

ABSTRACT: Citrus is an economically important fruit crop that is severely afflicted by citrus canker, a disease caused by Xanthomonas citri ssp. citri (X. citri); thus, new sustainable strategies to manage this disease are needed. Although all Citrus spp. are susceptible to this pathogen, they are resistant to other Xanthomonas species, exhibiting non-host resistance (NHR), for example, to the brassica pathogen X. campestris pv. campestris (Xcc) and a gene-for-gene host defence response (HDR) to the canker-causing X. fuscans ssp. aurantifolii (Xfa) strain C. Here, we examine the plant factors associated with the NHR of C. limon to Xcc. We show that Xcc induced asymptomatic type I NHR, allowing the bacterium to survive in a stationary phase in the non-host tissue. In C. limon, this NHR shared some similarities with HDR; both defence responses interfered with biofilm formation, and were associated with callose deposition, induction of the salicylic acid (SA) signalling pathway and the repression of abscisic acid (ABA) signalling. However, greater stomatal closure was seen during NHR than during HDR, together with different patterns of accumulation of reactive oxygen species and phenolic compounds and the expression of secondary metabolites. Overall, these differences, independent of Xcc type III effector proteins, could contribute to the higher protection elicited against canker development. We propose that Xcc may have the potential to steadily activate inducible defence responses. An understanding of these plant responses (and their triggers) may allow the development of a sustained and sustainable resistance to citrus canker.

SUBMITTER: Chiesa MA

PROVIDER: S-EPMC6637874 | biostudies-literature | 2019 Feb

REPOSITORIES: biostudies-literature

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Plant responses underlying nonhost resistance of Citrus limon against Xanthomonas campestris pv. campestris.

Chiesa María A MA Roeschlin Roxana A RA Favaro María A MA Uviedo Facundo F Campos-Beneyto Laura L D'Andrea Rodrigo R Gadea José J Marano María R MR

Molecular plant pathology 20181031 2

Citrus is an economically important fruit crop that is severely afflicted by citrus canker, a disease caused by Xanthomonas citri ssp. citri (X. citri); thus, new sustainable strategies to manage this disease are needed. Although all Citrus spp. are susceptible to this pathogen, they are resistant to other Xanthomonas species, exhibiting non-host resistance (NHR), for example, to the brassica pathogen X. campestris pv. campestris (Xcc) and a gene-for-gene host defence response (HDR) to the canke ...[more]

PMID: 30260546

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Project description:UnlabelledN-Acetylglucosamine (GlcNAc), the main component of chitin and a major constituent of bacterial peptidoglycan, is present only in trace amounts in plants, in contrast to the huge amount of various sugars that compose the polysaccharides of the plant cell wall. Thus, GlcNAc has not previously been considered a substrate exploited by phytopathogenic bacteria during plant infection. Xanthomonas campestris pv. campestris, the causal agent of black rot disease of Brassica plants, expresses a carbohydrate utilization system devoted to GlcNAc exploitation. In addition to genes involved in GlcNAc catabolism, this system codes for four TonB-dependent outer membrane transporters (TBDTs) and eight glycoside hydrolases. Expression of all these genes is under the control of GlcNAc. In vitro experiments showed that X. campestris pv. campestris exploits chitooligosaccharides, and there is indirect evidence that during the early stationary phase, X. campestris pv. campestris recycles bacterium-derived peptidoglycan/muropeptides. Results obtained also suggest that during plant infection and during growth in cabbage xylem sap, X. campestris pv. campestris encounters and metabolizes plant-derived GlcNAc-containing molecules. Specific TBDTs seem to be preferentially involved in the consumption of all these plant-, fungus- and bacterium-derived GlcNAc-containing molecules. This is the first evidence of GlcNAc consumption during infection by a phytopathogenic bacterium. Interestingly, N-glycans from plant N-glycosylated proteins are proposed to be substrates for glycoside hydrolases belonging to the X. campestris pv. campestris GlcNAc exploitation system. This observation extends the range of sources of GlcNAc metabolized by phytopathogenic bacteria during their life cycle.ImportanceDespite the central role of N-acetylglucosamine (GlcNAc) in nature, there is no evidence that phytopathogenic bacteria metabolize this compound during plant infection. Results obtained here suggest that Xanthomonas campestris pv. campestris, the causal agent of black rot disease on Brassica, encounters and metabolizes GlcNAc in planta and in vitro. Active and specific outer membrane transporters belonging to the TonB-dependent transporters family are proposed to import GlcNAc-containing complex molecules from the host, from the bacterium, and/or from the environment, and bacterial glycoside hydrolases induced by GlcNAc participate in their degradation. Our results extend the range of sources of GlcNAc metabolized by this phytopathogenic bacterium during its life cycle to include chitooligosaccharides that could originate from fungi or insects present in the plant environment, muropeptides leached during peptidoglycan recycling and bacterial lysis, and N-glycans from plant N-glycosylated proteins present in the plant cell wall as well as in xylem sap.

Dataset Information

Plant responses underlying nonhost resistance of Citrus limon against Xanthomonas campestris pv. campestris.

Publications

Plant responses underlying nonhost resistance of Citrus limon against Xanthomonas campestris pv. campestris.

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