Abstract
Grammicin, a polyketide metabolite produced by the endolichenic fungus Xylaria grammica KCTC 13121BP, shows strong nematicidal activity against Meloidogyne incognita. This study was performed to elucidate the grammicin biosynthesis pathway of X. grammica KCTC 13121BP and to examine the nematicidal activity of the biosynthesis intermediates and derivatives against M. incognita. Two grammicin biosynthesis intermediates were isolated from a T-DNA insertion transformant (strain TR-74) of X. grammica KCTC 13121BP and identified as 2-(hydroxymethyl)cyclohexa-2,5-diene-1,4-dione (compound 1) and 2,5-dihydroxybenzaldehyde (compound 2), which were also reported to be intermediates in the biosynthesis pathway of patulin, an isomer of grammicin. This indicates that the grammicin biosynthesis pathway overlaps almost with that of patulin, except for the last few steps. Among 13 grammicin biosynthesis intermediates and their derivatives (except grammicin), toluquinol caused the highest M. incognita J2 mortality, with an LC50/72 h value of 11.13 µg/mL, which is similar to grammicin with an LC50/72 h value of 15.95 µg/mL. In tomato pot experiments, the wettable powder type formulations (WP) of toluquinol (17.78 µg/mL) and grammicin (17.78 µg/mL) also effectively reduced gall formation on the roots of tomato plants with control values of 72.22% and 77.76%, respectively, which are much higher than abamectin (16.67%), but lower than fosthiazate (100%). The results suggest that toluquinol can be used directly as a biochemical nematicide or as a lead molecule for the development of new synthetic nematicides for the control of root-knot nematode diseases.
Highlights
Root-knot nematodes (RKNs) cause great harm to global agricultural productivity, reducing crop yields by 12–14% and causing global economic losses amounting to more than $125 billion—annually [1,2]
Chemical nematicides are the primary method of controlling nematode infections, the use of some of them is prohibited in several countries because of their negative impact on human health and the environment [4,5]
During the study on the elucidation of the biosynthetic pathway in the X. grammica KCTC 13121BP, we found that two substances isolated from X. grammica KCTC 13121BP transformant are patulin biosynthesis intermediates and toxic to the second-stage juveniles of Meloidogyne incognita, a causal agent of root-knot nematode diseases
Summary
Root-knot nematodes (RKNs) cause great harm to global agricultural productivity, reducing crop yields by 12–14% and causing global economic losses amounting to more than $125 billion—annually [1,2]. Substances produced by endophytic fungi have a variety of effects on plants, including growth promotion, increased resistance to disease, and an enhanced ability to withstand environmental stress [8]. Such metabolites have the potential to be used as biological control agents. Polyketide compounds include antibiotics, antifungals, anticancer agents, immunosuppressants, and anti-dyslipidemia agents They are clinically useful, and form the biologically active components of various substances used as agricultural growth-promoters, pesticides, and anthelmintics [10]. Polyketides are synthesized by a common biosynthesis mechanism [12]
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