Volatile Molecules Secreted by the Wheat Pathogen Parastagonospora nodorum Are Involved in Development and Phytotoxicity

Abstract

Septoria nodorum blotch is a major disease of wheat caused by the fungus Parastagonospora nodorum. Recent studies have demonstrated that secondary metabolites, including polyketides and non-ribosomal peptides, produced by the pathogen play important roles in disease and development. However, there is currently no knowledge on the composition or biological activity of the volatile organic compounds (VOCs) secreted by P. nodorum. To address this, we undertook a series of growth and phytotoxicity assays and demonstrated that P. nodorum VOCs inhibited bacterial growth, were phytotoxic and suppressed self-growth. Mass spectrometry analysis revealed that 3-methyl-1-butanol, 2-methyl-1-butanol, 2-methyl-1-propanol, and 2phenylethanol were dominant in the VOC mixture and phenotypic assays using these short chain alcohols confirmed that they were phytotoxic. Further analysis of the VOCs also identified the presence of multiple sesquiterpenes of which four were identified via mass spectrometry and nuclear magnetic resonance as β-elemene, α-cyperone, eudesma-4,11-diene and acora-4,9-diene. Subsequent reverse genetics studies were able to link these molecules to corresponding sesquiterpene synthases in the P. nodorum genome. However, despite extensive testing, these molecules were not involved in either of the growth inhibition or phytotoxicity phenotypes previously observed. Plant assays using mutants of the pathogen lacking the synthetic genes revealed that the identified sesquiterpenes were not required for disease formation on wheat leaves. Collectively, these data have significantly extended our knowledge of the VOCs in fungi and provided the basis for further dissecting the roles of sesquiterpenes in plant disease.

Pathogenicity effector candidates and accessory genome revealed by pan-genomic analysis of Parastagonospora nodorum

“…The SN15 reference isolate has predominated molecular plant pathology studies of P. nodorum since, becoming an important model for the cereal necrotrophs (Solomon et al 2006). Significant resources have accumulated over time for the SN15 isolate and P. nodorum in general, including transcriptomic (Hane et al 2007, Ipcho et al 2012, Syme et al 2016, Richards et al 2018, Jones et al 2019), proteomic (Bringans et al 2009, Syme et al 2016), and metabolomic (Lowe et al 2008, Gummer et al 2013, Chooi et al 2014, Muria-Gonzalez et al 2020) datasets. Notable recent additions to the growing pool of P. nodorum data include the chromosome-scale genome assemblies of SN15 and 3 other reference isolates (Richards et al 2018, Bertazzoni et al 2021).…”