A Wild Arachis Endochitinase Enhances Sclerotinia Resistance in Transgenic Plants

Plant endochitinases promote the cleavage of chitin, a polymer naturally found in the cell walls of fungi and insects. Although such enzymes are widely employed in plant genetic engineering to increase tolerance to pathogenic fungi, endochitinases from wild germplasm are poorly exploited for biotechnological purposes. Wild peanut species (Arachis spp.) have evolved under a range of environmental conditions and display distinct defensive adaptations, harboring high levels of genetic diversity and constituting an attractive source of resistance genes against pathogens. Arachis stenosperma shows broad resistance against various biotic stresses such as nematodes, fungi, and viruses. Previous transcriptome and proteomic studies on A. stenosperma challenged with fungi and nematodes identified differentially expressed genes (DEGs) involved in plant defense responses, including an upregulated endochitinase (AsECHI1). Here, we characterized endochitinases from 12 different legumes, including wild Arachis species, and evaluated the effects of overexpression of AsECHI1 for control of Sclerotinia sclerotiorum in tobacco, singly and in association with an expansin-like B defense-priming gene (AdEXLB8). Both singly and pyramided transgenic tobacco lines overexpressing AsECHI1 exhibited a delay in disease progression, and up to a 46% reduction in fungal lesions. Further analysis of transgenic plants showed that the overexpression of AsECHI1 led to an increased expression of defense-related genes in the jasmonic acid, auxin, and ethylene biosynthesis pathways, as well as a substantial accumulation of H₂O₂. These results suggest that the AsECHI1 gene isolated from wild Arachis has the potential to enhance resistance against this highly damaging necrotrophic fungal pathogen, reducing environmental damage related to the use of fungicides and increasing crop sustainability.