Transcriptome modulation by the beneficial fungus Trichoderma longibrachiatum drives water stress response and recovery in tomato

Trichoderma spp. are beneficial soil microorganisms used in sustainable agriculture for their ability to enhance plant performance under different environments. However, Trichoderma-activated mechanisms that help plants to cope with water stress are still not completely defined. We investigated morpho-physiological, biochemical and transcriptomic responses to PEG-induced short severe water stress in Trichoderma longibrachiatum-inoculated and non-inoculated Solanum lycopersicum. Trichoderma had significant biostimulation effects on the plant and, after stress, allowed recovery of growth and photosynthesis to the levels of unstressed plants. Whole-transcriptome analysis was carried out after 1 day of 15 % PEG treatment in 22-day Trichoderma-inoculated and non-inoculated plants. Under non-stress conditions, Trichoderma triggered an extensive transcriptional reprogramming, specifically modulating the expression of classes of transcription factors and of genes involved in photosynthesis, antioxidant defences and maintenance of a juvenile state. Though the effects of water stress were predominant, mainly boosting transcription of stress-responsive genes, pre-treatment with Trichoderma specifically affected genes involved in mitigation of stress damage. Our findings provide new insights into the plant interplay with Trichoderma, useful to further exploit rhizosphere fungi for the improvement of plant performance under limiting environments.