Trichoderma spp. Genes Involved in the Biocontrol Activity Against Rhizoctonia solani

Abstract

Rhizoctonia solani is a pathogen that causes considerable harm to plants worldwide. In the absence of hosts, R. solani survives in the soil by forming sclerotia, and management methods, such as cultivar breeding, crop rotations, and fungicide sprays, are insufficient and/or inefficient in controlling R. solani. One of the most challenging problems facing agriculture in the twenty-first century besides with the impact of global warming. Environmentally friendly techniques of crop production and improved agricultural practices are essential for long-term food security. Trichoderma spp. could serve as an excellent example of a model fungus to enhance crop productivity in a sustainable way. Among biocontrol mechanisms, mycoparasitism, competition, and antibiosis are the fundamental mechanisms by which Trichoderma spp. defend against R. solani, thereby preventing or obstructing its proliferation. Additionally, Trichoderma spp. induce a mixed induced systemic resistance (ISR) or systemic acquired resistance (SAR) in plants against R. solani, known as Trichoderma-ISR. Stimulation of every biocontrol mechanism involves Trichoderma spp. genes responsible for encoding secondary metabolites, siderophores, signaling molecules, enzymes for cell wall degradation, and plant growth regulators. Rhizoctonia solani biological control through genes of Trichoderma spp. is summarized in this paper. It also gives information on the Trichoderma-ISR in plants against R. solani. Nonetheless, fast-paced current research on Trichoderma spp. is required to properly utilize their true potential against diseases caused by R. solani.

Keywords: R. solani; Trichoderma spp.; antibiosis; competition; genes; induced systemic resistance; mycoparasitism.

Figure 1

Geographical distribution of Rhizoctonia solani.

Figure 2

Trichoderma spp. biocontrol mechanisms against R. solani. (A) Trichoderma spp. genes in antibiosis, (B) mycoparasitism, (C–E) competition for root colonization, rhizosphere and nutrients, and (F) induced systemic resistance.

Figure 3

Mycoparasitism; Trichoderma spp. (Green color) parasitize R. solani (purple) in soil. (A–C) Trichoderma spp. recognized R. solani by tiny molecules (oligopeptides and small other molecules); some of these molecules are peptides released by the action of proteases of Trichoderma spp. prior to contact. Also R. solani secrete ROS and secondary metabolites in response to Trichoderma spp. (D) These molecules bind to G protein-coupled receptors (GPCRs; such as Gpr1) or nitrogen-sensing receptors (Target of rapamycin; TOR pathway), or adenylate cyclase receptors on the surface of Trichoderma spp. hyphae. (E) After binding to the receptors, the molecules induce a signaling cascade involving G proteins and mitogen-activated protein kinases (MAPKs) or protein kinases (PKA), which then modulate the activities of transcription factors (TFs) and gene regulations. (F,G) These substances then boost the expression of genes that code for enzymes involved in secondary metabolite production and lysis of the cell wall of R. solani. Reconstructed from Druzhinina et al. (2011).

Figure 4

Trichoderma-induced systemic resistance (TISR) in plants against R. solani. Both SA and JA/ET-mediated signal transduction pathways may trigger defensive responses against R. solani, boosting plant resistance. Trichoderma spp. release enzymes to degrade plant polysaccharides, colonize the roots, and take sucrose as a carbon source by using sucrose permease and invertase enzymes. Trichoderma spp. produce elicitors, such as MAMPs to induce TISR in the plants; plants synthesize hydroperoxide lyase, peroxidase, and phenylalanine ammonia-lyase (which induces lignification) and deposit callose. Trichoderma MAMPs, such as xylanase, elicits plant defense responses against R. solani. The 1-aminocyclopropane-1-carboxylic acid (AAC) deaminase inhibits ethylene formation by the plant, and this leads to enhanced root growth, and this is due to the formation of hormones. Besides, Trichoderma spp. attach to plants roots by producing hydrophobins and swollenin. Reconstructed from Druzhinina et al. (2011).