The nematicide, fluensulfone, alters auxin responses in Arabidopsis

Abstract

Plant parasitic nematode (PPN) species are estimated to cause a 12.3% annual yield reduction of economically important crops making it essential that new mechanisms are found to control these pests. The new generation nematicide, fluensulfone (Nimitz®), displays potent nematicidal activity towards PPNs, including root-knot nematode Meloidogyne spp. and potato cyst nematode, G. pallida. In comparison to phased out nematicides and existing organophosphate- and carbamate-based nematicides, fluensulfone has a significantly reduced environmental impact. The mode of action of fluensulfone remains to be elucidated but preliminary experiments indicated that fluensulfone had biological effects on Arabidopsis thaliana, we therefore used Arabidopsis as a system to identify the molecular targets of fluensulfone.

Application of exogenous fluensulfone resulted in reduced seedling growth in the light. However, application in the absence of light induced de-etiolation, characterized by inhibition of hypocotyl elongation, cotyledon opening and accumulation of the chlorophyll precursor, protochlorophyllide. Co-treatment with both natural (IAA) and synthetic auxins (1-NAA, 2,4-D) were able to partially rescue this phenotype, but application of other phytohormones did not. RNAseq analysis demonstrated differential expression of 7820 and 2666 genes following fluensulfone treatment in the light and dark, respectively. Functional analysis based on gene ontology (GO) terms indicated enrichment of auxin-associated terms within these differentially expressed gene sets and data set comparisons indicated significant overlap in gene expression profiles after treatment with various auxin related compounds. Three fluorescent reporter lines were also used to demonstrate a reduction in auxin signalling at the root tip with auxin-induced degradation of the DII::VENUS reporter being prevented following fluensulfone treatment for as little as 15 minutes. Furthermore, comparisons with established auxin receptor antagonist, auxinole, displayed a similar de-etiolated phenotype and inhibition of the DII::VENUS reporter degradation. Together our results suggest that one primary effect of fluensulfone is a rapid alteration of the auxin response in Arabidopsis.

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ORCID for Matthew Terry: orcid.org/0000-0001-5002-2708

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