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bioRxiv2024

Characterisation of aphid antixenosis in aphid-resistant ancestor wheat, Triticum monococcum

BACKGROUNDDue to the increasing presence of insecticide resistance across cereal aphid populations, new aphid management strategies, including the engineering of host resistance to aphids into commercial wheat varieties, are required. Previous studies have identified ancestor wheat, Triticum monococcum accessions MDR045 and MDR049, with resistance against the grain aphid, Sitobion avenae. To test the hypothesis that resistance can be accounted for by antixenosis (reduced attractiveness of host plants) via the release of repellent volatile organic compounds (VOCs), we explored the response of S. avenae to MDR045 and MDR049 following S. avenae herbivory, using behaviour and electrophysiology experiments. RESULTSIn four-arm olfactometry assays, alate S. avenae showed aphid-density dependent reduced preference to VOC extracts from T. monococcum MDR045 and MDR049. By contrast, alate S. avenae showed aphid-density dependent increased preference to extracts from hexaploid wheat, T. aestivum var Solstice and T. monococcum MDR037. Coupled gas chromatography-electroantennography (GC- EAG), using the antennae of alate S. avenae, located 24 electrophysiologically active compounds across all tested accessions. Synthetic blends created from 21 identified EAG-active compounds confirmed bioactivity of corresponding VOC extracts in four-arm olfactometry assays against alate S. avenae. CONCLUSIONOur data suggest that resistance of T. monococcum MDR045 and MDR049 to S. avenae can be at least partially accounted for by antixenosis, through antennal perception of specific repellent VOC blends induced by S. avenae feeding behaviour.

ecology↗

bioRxiv2023

Chemical cues from beetle larvae trigger proliferation and virulence of a plant pathogen

Agricultural crop productivity and global forest biomes are coming under increasing threat from insect pests and microbial pathogens. This impact is worsened by inter- kingdom insect-microbe interactions that can increase transmission and disease severity in affected plants. Whilst bacterial chemical cues have been shown to directly influence insect behaviour, the impact of insect-derived compounds on phytopathogens is poorly understood. Here, we investigated the chemical basis for interactions between beetle larvae and bacteria in acute oak decline (AOD), a disease characterised by inner bark necrosis and involving a polymicrobial consortium including Brenneria goodwinii and larval galleries of Agrilus biguttatus. We found that A. biguttatus larval extracts contain chemical elicitors that increase bacterial growth rate and final cell density during in vitro culture, and stimulate the differential expression of [~]600 genes, including the Type III Secretion System and its effectors, which are major virulence factors in plant pathogens. Chemical compounds from closely related insect species did not have this effect. These findings highlight the importance of inter-kingdom interactions in plant disease and suggests a novel mode-of-action for insect-derived chemical elicitors in facilitating the virulence of phytopathogens.

ecology↗