Heteroconium chaetospira Induces Resistance to Clubroot via Upregulation of Host Genes Involved in Jasmonic Acid, Ethylene, and Auxin Biosynthesis

Abstract

An endophytic fungus, Heteroconium chaetospira isolate BC2HB1 (Hc), suppressed clubroot (Plasmodiophora brassicae -Pb) on canola in growth-cabinet trials. Confocal microscopy demonstrated that Hc penetrated canola roots and colonized cortical tissues. Based on qPCR analysis, the amount of Hc DNA found in canola roots at 14 days after treatment was negatively correlated (r = 0.92, P<0.001) with the severity of clubroot at 5 weeks after treatment at a low (2×105 spores pot−1) but not high (2×105 spores pot−1) dose of pathogen inoculum. Transcript levels of nine B. napus (Bn) genes in roots treated with Hc plus Pb, Pb alone and a nontreated control were analyzed using qPCR supplemented with biochemical analysis for the activity of phenylalanine ammonia lyases (PAL). These genes encode enzymes involved in several biosynthetic pathways related potentially to plant defence. Hc plus Pb increased the activity of PAL but not that of the other two genes (BnCCR and BnOPCL) involved also in phenylpropanoid biosynthesis, relative to Pb inoculation alone. In contrast, expression of several genes involved in the jasmonic acid (BnOPR2), ethylene (BnACO), auxin (BnAAO1), and PR-2 protein (BnPR-2) biosynthesis were upregulated by 63, 48, 3, and 3 fold, respectively, by Hc plus Pb over Pb alone. This indicates that these genes may be involved in inducing resistance in canola by Hc against clubroot. The upregulation of BnAAO1 appears to be related to both pathogenesis of clubroot and induced defence mechanisms in canola roots. This is the first report on regulation of specific host genes involved in induced plant resistance by a non-mycorrhizal endophyte.

The Effectiveness of a Dark Septate Endophytic Fungus, Cladophialophora chaetospira SK51, to Mitigate Strawberry Fusarium Wilt Disease and With Growth Promotion Activities

“…Heteroconium chaetospira (Grove) M. B. Ellis has been reported to suppress clubroot disease in Chinese cabbage plants (Narisawa et al, 2005). Lahlali et al (2014) reported that Heteroconium chaetospira (syn. C. chaetospira) suppressed clubroot (Plasmodiophora brassicae) disease via the upregulation of host genes involved in jasmonic acid, ethylene, and auxin biosynthesis.…”

Analysis of salicylic acid‐dependent pathways in Arabidopsis thaliana following infection with Plasmodiophora brassicae and the influence of salicylic acid on disease

“…SA treatment alone does not seem to be sufficient. One solution could be by biocontrol organisms, which could induce the plant's immune system, as shown for the interaction of Brassica napus with P. brassicae, where JA/ethylene pathways could be induced (Lahlali et al, 2014).…”

Endophytic fungi as biocontrol agents: elucidating mechanisms in disease suppression

“…PR genes and JAdependent genes were not differentially regulated (Su et al 2013). A similar study on a dark-septate endophyte on oilseed rape was carried out by Lahlali et al (2014), in which PR-2 (β-1,3-glucanase) and PAL was up-regulated when the plants were inoculated with the endophyte before inoculation with Plasmodiophora brassicae.…”

“…Since the control effect is only local, it would require a systemic colonisation of the host plant part where the pathogen might attack. Correspondingly, colonisation of oilseed rape roots with the dark-septate endophyte Heteroconium chaetospira, measured by qPCR, was negatively correlated to clubroot symptoms (Lahlali et al 2014). However, increased pathogen inoculum reduced the control effect, indicating the limitation of competition as a mechanism under high disease pressure.…”

“…These PR proteins include enzymes and peptides such as thionins, lipid-transfer proteins and thaumatin-like proteins (van Loon and van Strien 1999;Sels et al 2008). For example, β-1,3-glucanase (PR-2) was up-regulated in Plasmodiophora brassicae infected oilseed rape plants when colonised by the dark septate endophyte Heteroconium chaetospira (Lahlali et al 2014). Likewise, endophytic Fusarium solani (strain Fs-K) induced systemic resistance in tomato against Fusarium oxysporum f.sp.…”