The volatile cedrene from Trichoderma guizhouense modulates Arabidopsis root development through auxin transport and signalling

Rhizosphere microorganisms interact with plant roots by producing chemical signals that regulate root development. However, the distinct bioactive compounds and signal transduction pathways remain to be identified. Here, we showed that sesquiterpenes are the main volatile compounds produced by plant-beneficial Trichoderma guizhouense NJAU4742. Inhibition of sesquiterpene biosynthesis eliminated the promoting effect of this strain on root growth, indicating its involvement in plant-fungus cross-kingdom signalling. Sesquiterpene component analysis identified cedrene, a highly abundant sesquiterpene in strain NJAU4742, to stimulate plant growth and root development. Genetic analysis and auxin transport inhibition showed that the TIR1 and AFB2 auxin receptors, IAA14 auxin-responsive protein, and ARF7 and ARF19 transcription factors affected the response of lateral roots to cedrene. Moreover, the AUX1 auxin influx carrier and PIN2 efflux carrier were also found to be indispensable for cedrene-induced lateral root formation. Confocal imaging showed that cedrene affected the expression of pPIN2:PIN2:GFP and pPIN3:PIN3:GFP, which might be related to the effect of cedrene on root morphology. These results suggested that a novel sesquiterpene molecule from plant-beneficial T. guizhouense regulates plant root development through the transport and signalling of auxin.