The novel nematicide chiricanine A suppresses Bursaphelenchus xylophilus pathogenicity in Pinus massoniana by inhibiting Aspergillus and its secondary metabolite, sterigmatocystin

Abstract

IntroductionPine wilt disease (PWD) is responsible for extensive economic and ecological damage to Pinus spp. forests and plantations worldwide. PWD is caused by the pine wood nematode (PWN, Bursaphelenchus xylophilus) and transmitted into pine trees by a vector insect, the Japanese pine sawyer (JPS, Monochamus alternatus). Host infection by PWN will attract JPS to spawn, which leads to the co-existence of PWN and JPS within the host tree, an essential precondition for PWD outbreaks. Through the action of their metabolites, microbes can manipulate the co-existence of PWN and JPS, but our understanding on how key microorganisms engage in this process remains limited, which severely hinders the exploration and utilization of promising microbial resources in the prevention and control of PWD.MethodsIn this study we investigated how the PWN-associated fungus Aspergillus promotes the co-existence of PWN and JPS in the host trees (Pinus massoniana) via its secondary metabolite, sterigmatocystin (ST), by taking a multi-omics approach (phenomics, transcriptomics, microbiome, and metabolomics).ResultsWe found that Aspergillus was able to promote PWN invasion and pathogenicity by increasing ST biosynthesis in the host plant, mainly by suppressing the accumulation of ROS (reactive oxygen species) in plant tissues that could counter PWN. Further, ST accumulation triggered the biosynthesis of VOC (volatile organic compounds) that attracts JPS and drives the coexistence of PWN and JPS in the host plant, thereby encouraging the local transmission of PWD. Meanwhile, we show that application of an Aspergillus inhibitor (chiricanine A treatment) results in the absence of Aspergillus and decreases the in vivo ST amount, thereby sharply restricting the PWN development in host. This further proved that Aspergillus is vital and sufficient for promoting PWD transmission.DiscussionAltogether, these results document, for the first time, how the function of Aspergillus and its metabolite ST is involved in the entire PWD transmission chain, in addition to providing a novel and long-term effective nematicide for better PWD control in the field.

The molecular basis of pine wilt disease resistance inPinus massoniana

“…The antioxidant effects of monoterpenes and sesquiterpenes also alleviate oxidative stress caused by PWN infection (Farhadi et al, 2020; Son et al, 2023). However, the common response is insufficient in limiting the PWN, possibly because it may detoxify secondary metabolites (including terpenoid compounds) (Jia et al, 2023). In future studies, adding monoterpenes and sesquiterpenes to the diet of the PWN and observing mortality may indicate whether the PWN has a detoxification system.…”

“…These substances have antioxidant and antimicrobial functions that limit PWN pathogenicity and microbial infection (Raorane et al, 2019; Liu et al, 2023b). Pine wilt nematode pathogenicity involves numerous symbiotic or associated microbes (Jia et al, 2023). Flavonoids affect the environment for nematodes by inhibiting the growth of certain pathogenic microbes or regulating the structure of beneficial microbial communities (Borah et al, 2018).…”

“…Previous research and empirical evidence have revealed that PWN pathogenicity begins with its proliferation in the xylem of pine trees, which causes mechanical damage (Ichihara et al, 2000; Umebayashi et al, 2011; Yazaki et al, 2018). Additionally, PWN is often accompanied by other pathogens (such as fungi), and co-infection exacerbates the damage to pine trees (Xue et al, 2019; Jia et al, 2023). Proteases and polysaccharide enzymes are secreted by PWN, and these toxins disrupt cellular structure, interfere with normal physiological functions, and lead to tree death (Zhao et al, 2007; Faria et al, 2015).…”