The assembly of a Malus sieversii regulatory network reveals gene resistance against Alternaria alternata f. sp. mali when colonized by Trichoderma biofertilizer.

Abstract

Trichoderma spp., as excellent biocontrol agents, can induce systemic resistance to protect plants from phytopathogen attacks. In a previous study, Trichoderma biofertilizer activated the MsERF105 transcription factor (TF), which further enhanced the resistance of Malus sieversii against Alternaria alternata f. sp. mali, but how resistance signals are transmitted is still unknown. In this study, it was found that the MsERF105-centered disease-resistant regulatory network was induced by Trichoderma in M. sieversii. The TF-centered yeast one-hybrid indicated that WRKY33 and WRKY40 bound to WBOXATNPR1 elements and GT1 bound to GT1CONSENSUS elements in the promoter of MsERF105 to activate its expression. In addition, the proteins that interacted with MsERF105 were identified by yeast two-hybrid, including FUBP2 and HSP17.8. Furthermore, the candidate target genes of MsERF105 were screened using RNA-Seq, and yeast one-hybrid and tobacco transient transformation further showed MsERF105 bound to GCCBOX elements to regulate the expression of bHLH162, ERF017, NAC83 and NAC104; bound to CCAATBOX elements to regulate the expression of HSFs, HSP70s and HSP20; and bound to ERS elements to regulate the expression of DRPs. Finally, the Trichoderma-induced MsERF105-centered regulatory network of M. sieversii against A. alternata f. sp. mali was built, which provided reliable theoretical guidance for the application of Trichoderma and the disease-resistance breeding of M. sieversii.