Ectopic expression of an expansin‐like B gene from wild Arachis enhances tolerance to both abiotic and biotic stresses

Abstract

Plant expansins are structural cell wall-loosening proteins implicated in several developmental processes and responses to environmental constraints and pathogen infection. To date, there is limited information about the biological function of expansins-like B (EXLBs), one of the smallest and less-studied subfamilies of plant expansins. In the present study, we conducted a functional analysis of the wild Arachis AdEXLB8 gene in transgenic tobacco (Nicotiana tabacum) plants to clarify its putative role in mediating defense responses to abiotic and biotic stresses. First, its cell wall localization was confirmed in plants expressing an AdEXLB8:eGFP fusion protein, while nanomechanical assays indicated cell wall reorganization and reassembly due to AdEXLB8 overexpression without compromising the phenotype. We further demonstrated that AdEXLB8 increased tolerance not only to isolated abiotic (drought) and biotic (Sclerotinia sclerotiorum and Meloidogyne incognita) stresses but also to their combination. The jasmonate and abscisic acid signaling pathways were clearly favored in transgenic plants, showing an activated antioxidative defense system. In addition to modifications in the biomechanical properties of the cell wall, we propose that AdEXLB8 overexpression interferes with phytohormone dynamics leading to a defense primed state, which culminates in plant defense responses against isolated and combined abiotic and biotic stresses.

Transcriptome Responses of Wild Arachis to UV-C Exposure Reveal Genes Involved in General Plant Defense and Priming

“…Plant expansins are involved in cell wall loosening and are active components of stress-associated responses, commonly related to defense priming processes [ 8 , 57 ]. Moreover, the upregulation of EXLB and EGC genes is consistent with our recent findings that the overexpression of an A. duranensis EXLB gene enhanced tolerance to abiotic and biotic stresses by mediating the induction of a defense primed state [ 100 ].…”

A novel soybean hairy root system for gene functional validation

“…Conversely, very few reports showed the involvement of α-Expansins in both compatible and incompatible plant-microbe interactions [ 35 , 72 – 76 ]. Recently, some studies also demonstrated the putative role of the Expansin superfamily in mediating resistance responses to simultaneous abiotic and biotic stresses (cross-stress) as well as in defense priming processes and stress memory [ 35 , 77 – 81 ]. Our findings support those studies by showing that AdEXPA24 overexpression improves resistance against Meloidogyne sp.…”

Mechanisms of plant cell wall surveillance in response to pathogens, cell wall-derived ligands and the effect of expansins to infection resistance or susceptibility

“…As mentioned before, signs of cell wall modification due to microbial activity or induced by abiotic stress are detected by membrane receptors alerting the cell to mount defense and stress responses, sometimes simultaneously. For instance, ectopic overexpression of EXLB8 from Arachis in tobacco results in tolerance to water deficit and resistance to the white mold causative necrotrophic fungus [ Sclerotinia sclerotiorum ( Hegedus and Rimmer, 2005 )], and to the nematode M. incognita , and to drought and simultaneous nematode infection ( Brasileiro et al, 2021 ). Different cell wall nanomechanical properties (possibly stiffer, but more deformable leaves), brought about by EXLB8 overexpression, and consequently, possibly by other six endogenous EXL genes, was suggested as responsible of the phenotype hampering a successful infection.…”

“…Different cell wall nanomechanical properties (possibly stiffer, but more deformable leaves), brought about by EXLB8 overexpression, and consequently, possibly by other six endogenous EXL genes, was suggested as responsible of the phenotype hampering a successful infection. Various biotic and abiotic stress genes of the jasmonate, ethylene and abscisic acid pathways were also induced, activating a more general and unspecific priming of the host against pathogens with important lifestyle differences ( Brasileiro et al, 2021 ). Contrarily, A. thaliana EXLA2 down-regulation provides resistance to B. cinerea and oxidative stress, although roots become sensitive to salt and cold when the medium contains ABA ( Abuqamar et al, 2013 ).…”