| Abstract | Plant-microbe interactions are key to improving plant defence against herbivory which causes significant losses in food production worldwide. This project aimed to study how aphid herbivory changes the chemical signalling at the plant-soil microbe interface, and to disentangle the complexity of these interactions using a multidisciplinary approach involving microbiology, chemical ecology and bioinformatics.
In an initial experiment where wheat plants were exposed to aphid herbivory for two weeks, rhizosphere bacterial diversity was observed to decrease, with an increased the relative abundance of Actinobacteria class (p < 0.05). Furthermore, untargeted metabolomics analyses showed that the profile of volatile organic compounds (VOCs) in the rhizosphere soil was significantly different under herbivory (p < 0.05). Based on these findings, a second experiment was design using a semi-hydroponic system to facilitate the analysis of chemical signals released by plants via root exudates and volatile organic compounds. Furthermore, rhizosphere and root tissue collection were performed for DNA extraction and amplicon sequencing analysis (16S rRNA). The metabolomics analysis showed that aphid herbivory induced significant changes in the root exudate profile, with 485 metabolites altered and 39 compounds significantly enriched under herbivory. Chemical classification revealed that some of these compounds belong to the benzoxazinoids, terpenes, coumarins and flavonoid classes of secondary metabolites, with some – like HMBOA – previously identified as key signals in plant-microbe interactions under herbivory. In contrast, herbivory resulted in the depletion of certain oxidised fatty acids and amino acids in root exudates. Amplicon sequencing revealed that, some Actinobacteria genera found in the initial experiment (Streptacidiphilus, Streptomyces, Catenulispora), were enriched in the roots of plants under herbivory. Further investigations demonstrated that four herbivory-regulated compounds influenced the growth of rhizosphere bacteria isolated from wheat rhizosphere, suggesting that these metabolites play a functional role in shaping plant-microbe interactions.
Overall, this work shows that aboveground insect pests can have a significant impact on plant belowground interactions, and further research is needed to investigate how to use this knowledge for the development of sustainable pest management strategies that put the soil microbial communities at the centre of crop production. |
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