Cross-communication between Trichoderma and plants during root colonisation

Abstract

Fungi of the genus Trichoderma are found in soils worldwide and have a range of lifestyles that bring them into interaction with agriculturally relevant plants. Trichoderma virens is a potential endophyte, and may be suitable for application as a bio-control agent due to its mycoparasitic ability. However, little is understood about the nature of T. virens’ interactions with plant hosts. In this study, using Zea mays as an agriculturally relevant plant model, the nature of the interaction between Trichoderma and its plant hosts was examined. A novel interaction system, in sterile soil was established and maize hybrid line was determined to significantly affect T. virens colonisation. Microscopic analysis was used to visualise the ability of T. virens to penetrate, colonise and persist in the host plant. Appressoria-like structures were observed, and intra- and inter-cellular growth patterns were identified. Genomic and transcriptomic analyses were used to screen for potential effector proteins and other bioactive molecules involved in plant-fungal communication. T. virens communication with its host plant appears to be more reliant on lytic enzymes, polysaccharides and secondary metabolites than previously suspected, potentially reflecting its genetic origins as a saprobe. The expression of a large number of lytic enzymes by T. virens suggests that damage associated molecular pattern pathways would act as the primary elicitors of a plant response in maize during T. virens colonisation. Attempts to verify the role of lytic enzymes using an XlnR1 deletion mutant proved difficult due to ectopic recombination of deletion constructs; however the process yielded an enhanced protoplasting method for T. virens that was subsequently adopted by the wider research group. In summary, this work identified novel information on the mechanisms used by T. virens to successfully colonise host plants during an endophytic interaction.