Transcriptomic and biochemical analyses reveal wheat drought mitigation by Trichoderma simmonsii and reduced demand for canonical plant stress responses

The mechanisms through which Trichoderma helps plants to cope water stress (WS) are still unclear. Here, we investigated physiological, biochemical and transcriptomic responses to WS, and after rehydration, in T. simmonsii-treated wheat (Triticum aestivum) plants. RNA-sequencing analysis was performed when plants were 24 days old. WS consisted in removing irrigation for 10 days in 14-day-old plants, and rehydration was performed by optimal irrigation for three days. Rubisco genes were upregulated in Trichoderma-inoculated plants in comparison with those untreated, independently of the irrigation condition. Under WS condition, 1,913 differentially expressed genes (DEGs), many of them involved in pathways related to plant stress responses, were associated with the Trichoderma application. "Carbohydrate metabolism" and "photosynthesis" were the main functional categories overrepresented of upregulated DEGs when comparing Trichoderma" WS and control-WS plants. Such upregulation was accompanied by downregulation of genes involved in biosynthesis of abscisic acid, osmolytes like proline and trehalose, and non-enzymatic antioxidants, in WS Trichoderma-treated plants. These results together with a healthy phenotype and biochemical measurements indicate a minimal activation of responses to WS in Trichoderma-treated plants. We detected 57 transcription factor genes differentially expressed between Trichoderma-WS and control-WS treatments, with overrepresented members of WRKY, MYB, betaHLH, NAC and C2H2 families. Our findings provide valuable insights on the beneficial effect of Trichoderma in wheat plants subjected to drought, an environmental scenario that is increasing with global warming.