Xanthan Induces Plant Susceptibility by Suppressing Callose Deposition

Abstract

Xanthan is the major exopolysaccharide secreted by Xanthomonas spp. Despite its diverse roles in bacterial pathogenesis of plants, little is known about the real implication of this molecule in Xanthomonas pathogenesis. In this study we show that in contrast to Xanthomonas campestris pv campestris strain 8004 (wild type), the xanthan minus mutant (strain 8397) and the mutant strain 8396, which is producing truncated xanthan, fail to cause disease in both Nicotiana benthamiana and Arabidopsis (Arabidopsis thaliana) plants. In contrast to wild type, 8397 and 8396 strains induce callose deposition in N. benthamiana and Arabidopsis plants. Interestingly, treatment with xanthan but not truncated xanthan, suppresses the accumulation of callose and enhances the susceptibility of both N. benthamiana and Arabidopsis plants to 8397 and 8396 mutant strains. Finally, in concordance, we also show that treatment with an inhibitor of callose deposition previous to infection induces susceptibility to 8397 and 8396 strains. Thus, xanthan suppression effect on callose deposition seems to be important for Xanthomonas infectivity.

Botrytis cinerea Manipulates the Antagonistic Effects between Immune Pathways to Promote Disease Development in Tomato

“…As several EPSs are plant defense suppressors (Yun et al, 2006;Rigano et al, 2007), we then investigated if b-(1,3)(1,6)-Dglucan suppresses JA-dependent defense markers (PI I and II) induced by isolate B8403 in tomato. Five-week-old tomato plants were pretreated with either water or EPS 24 h before inoculation, which was performed by spraying the plants with spores (10 6 spores/mL) of either isolate.…”

“…EPSs are high molecular weight carbohydrates that are produced by several pathogenic fungi and bacteria. They have been established as key virulence factors, and some are involved in suppression of plant immune responses (Yun et al, 2006;Rigano et al, 2007). We purified the EPS from the virulent isolate B191, as described in Methods.…”

“…Many pathogens inject a set of effector proteins into host cells through the type III secretion system to interfere with host innate immunity (Hann et al, 2010). These effectors and other virulence factors, including exopolysaccharides, have several targets for suppression, including the hypersensitive response, expression of defense-related genes, cell wall-based defenses, the plant proteasome system, stomatal closure, and the PAMP receptor (Bouarab et al, 2002;Abramovitch and Martin, 2005;Chisholm et al, 2006;Janjusevic et al, 2006;Nomura, 2006;Yun et al, 2006;Rigano et al, 2007;Hann et al, 2010). P. syringae manipulates the antagonistic effect between SA and JA to cause disease by producing an analog of JA (Brooks et al, 2005;Cui et al, 2005;Laurie-Berry et al, 2006).…”

Glyceraldehyde-3-phosphate dehydrogenase of Xanthomonas campestris pv. campestris is required for extracellular polysaccharide production and full virulence

“…EPS has been shown to act as an important virulence factor in Xcc. It can enhance the susceptibility of host plants by suppressing defence responses such as callose formation (Yun et al, 2006), and contribute to biofilm formation (Dow et al, 2003) and bacterial resistance against host defences. It may also serve to mask the bacterium to prevent recognition by the host and to enable colonization of host tissues (Alvarez, 2000).…”

Systems and synthetic biology perspective of the versatile plant-pathogenic and polysaccharide-producing bacterium Xanthomonas campestris

“…Xanthan is not essential for the infection of citrus plants but it contributes to the epiphytic survival of the pathogen [59]. Xanthan secreted by Xcc suppresses the deposition of callose, a plant polysaccharide, and induces susceptibility to pathogenesis [60]. The signal transduction of plants, which is initiated in response to the specific detection of bacterial pathogens based on microbe-associated molecular patterns (MAMPs), has been described to be suppressed by xanthan due to polyanionic features facilitating calcium ion binding [61].…”