Root Colonisation and Induction of Plant Defence-associated Signalling Pathways Genes in Arabidopsis thaliana by...

We sought to determine whether Streptomyces albidoflavus CFFSUR-B12, Serratia marcescens CFFSUR-B2, and Trichoderma sp. CFFSUR-A21-strains recognised for their antagonistic capacity against tropical phytopathogenic fungi-could colonise the roots of and induce the expression of key induced systemic resistance (ISR) genes in Arabidopsis thaliana Col-0. These strains employ different mechanisms of direct antagonistic action against phytopathogenic fungi, so if they are capable of activating ISR, they would activate it in different ways. The antagonistic activity against Colletotrichum M07-C2 or M10-F2 strains was determined in dual-culture assays, where S. albidoflavus CFFSUR-B12 (75%), Trichoderma sp. CFFSUR-A21 (70%) and S. marcescens CFFSUR-B2 (46%) inhibited mycelial growth. Strains were inoculated separately in the roots of A. thaliana Col-0 to study root colonisation and activation of ISR in leaves. PR1 and PDF1.2 expression (as markers for the expression of the salicylic acid and the ethylene/jasmonic-acid signalling pathways, respectively) were monitored by RT-qPCR in leaves. Serratia marcescens CFFSUR-B2 colonised the rhizoplane and endorhizosphere, whereas S. albidoflavus CFFSUR-B12 and Trichoderma sp. CFFSUR-A21 only colonised the rhizoplane. Serratia marcescens CFFSUR-B2 and Trichoderma sp. CFFSUR-A21 induced co-expression of PR1 and PDF1.2 at 48 h, while S. albidoflavus CFFSUR-B12 induced only PDF1.2 expression at 24 h. Still, the pathogenic Colletotrichum M07-C2 or M10-F2 strains only induced the expression of PR1 after 72 h. These findings reveal new avenues for research into plant disease management in the humid tropics.