Analysis of the defence-related mechanism in cucumber seedlings in relation to root colonization by nonpathogenicFusarium oxysporumCS-20

Abstract

A defence response can be induced by nonpathogenic Fusarium oxysporum CS-20 in several crops, but the molecular mechanism has not been clearly demonstrated. In the present study, we analysed the defence mechanism of a susceptible cucumber cultivar (Cucumis sativus L. 9930) against a pathogen (F. oxysporum f. sp. cucumerinum) through the root precolonization of CS-20. A challenge inoculation assay indicated that the disease severity index (DSI) was reduced, ranging from 18.83 to 61.67 in comparison with the pathogen control. Root colonization analysis indicated that CS-20 clearly did not appear to influence the growth of cucumber seedlings. Quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR) revealed that CS-20-mediated defence response was activated by PR3, LOX1 and PAL1 and the pathogenmediated resistance response was regulated by PR1 and PR3. Moreover, both nonpathogenic and pathogenic F. oxysporum were able to upregulate NPR1 expression. In contrast to a pathogen, CS-20 can activate the Ca 2+ /CaM signal transduction pathway, and the gene expression of both CsCam7 and CsCam12 increased significantly. The gene expression analysis indicated that CS-20 strongly enhanced the expression of PR3, LOX1, PAL1, NPR1, CsCam7 and CsCam12 after inoculation. Overall, the defence response induced by CS-20 can be controlled by multiple genes in the cucumber plant.

Correlation between cucumber genotype and resistance to damping-off disease caused by Phytophthora melonis

“…JA is known to play major roles in the regulation of the plant immune system. Pathogen-induced LOX transcript accumulation has been reported in cucumber after inoculation with F. oxysporum CS-20 [45]. Although, this interaction is not the same, we found a similar pattern in our experiment, in which LOX1 showed activation after inoculation with P. melonis.…”

Biocontrol by Fusarium oxysporum Using Endophyte-Mediated Resistance

“…In contrast, in cucumber roots CS-20 did induce major transcriptional changes, and at 72 hpi there was a strong induction of PR3, LOX1, PAL1, and NPR1 and of CaMs, CsCam7 and CsCam12 being the strongest induced. At the same time point pathogenic Foc induced NPR1 and to a lesser extent PR3 and PAL1 expression (Pu et al, 2014). RNA-seq analysis of soybean roots inoculated with endophytic or pathogenic Fo revealed that the latter induced more, and stronger, transcriptional changes at 72 and 96 hpi (Lanubile et al, 2015).…”

“…This difference indicates that even at later stages of root colonization Fo47 does not reach the vasculature. Contrarily, Fo47 was reported to colonize xylem vessels of eucalyptus (Salerno et al, 2000) and the Fo endophyte CS-20 was found to colonize xylem vessels of cucumber (Pu et al, 2014). An explanation for the vascular presence of the latter two endophytic strains could be the clipping of the roots prior to inoculation, providing direct vascular access to the endophyte.…”

“…Fusarium Induces Root-Specific Resistance application (Olivain et al, 2003). Ca 2+ influx activates calmodulin (CaM), and in cucumber roots the CaM signal transduction pathway was more strongly induced upon CS-20 colonization than when treated with pathogenic Foc (Pu et al, 2014), implying a weaker PTI induction by pathogenic strains. ROS, besides being signaling molecules, have direct toxic effects on microbes (O'Brien et al, 2012) and can induce cell death thereby limiting progression of biotrophic pathogens (Mur et al, 2008).…”

“…However, genetically encoded resistance is seldom durable and sooner or later new races emerge that overcome resistance in a never-ending arms race between Fo and its host (Takken and Rep, 2010;de Sain and Rep, 2015). Furthermore, Fo resistance genes are not available in the germplasm of all crops or they cannot be introgressed by breeding (Ploetz, 2015).…”