Apple replant disease is a complex soil syndrome that occurs when the same fields are repeatedly utilized for apple orchard cultivation. It can be caused by various pathogens, and Fusarium solani is the main pathogen. Fusarium solani disrupts the structure and function of the orchard soil ecosystem and inhibits the growth and development of apple trees, significantly impacting the quality and yield of apples. In this study, we conducted a transcriptome comparison between uninoculated apple saplings and those inoculated with F. solani. The differentially expressed genes were mainly enriched in processes such as response to symbiotic fungus. Plant defensins are antimicrobial peptides, but their roles during F. solani infection remain unclear. We performed a genome-wide identification of apple defensin genes and identified 25 genes with the conserved motif of eight cysteine residues. In wild- type apple rootstock inoculated with F. solani, the root surface cells experienced severe damage, and showed significant differences in the total root length, total root projection area, root tips, root forks, and total root surface area compared to the control group. qRT-PCR analysis revealed that MdDEF3 and MdDEF25 were triggered in response to F. solani infection in apples. Subcellular localization showed specific expression of the MdDEF3-YFP and MdDEF25-YFP proteins on the cell membrane. Overexpressing the MdDEF25-YFP fusion gene enhanced resistance against F. solani in apple, providing a new strategy for the future prevention and biological control of apple replant disease.

Root rot is a soil-borne disease primarily caused by fungi. The malady not only decrease the ability of absorbing water and nutrients, but also severely threat agricultural productivity. Recently, a new family member of twodimensional (2D) transition metal carbide materials, MXene (Ti3C2Tx), has gained much interest as a promising approach to control fungi. However, the efficient use and mechanism of MXene in protecting plant against pathogenic fungus are still rarely reported. Here, the synthesized MXene were first characterized by the atomic force microscopy (AFM), scanning electron microscopy (SEM), dynamic light scattering (DLS), transmission electron microscopy (TEM) and X-ray photoelectron spectra (XPS). MXene application in soil obviously enhanced the root rot disease resistance of T. grandis. Soil microbial community analysis indicated that the abundance of Fusasium genus was decreased by 68.32% after MXene treatment. Further, MXene specially affected the permeability of Fusarium solani via damaging their cell membranes, thereby causing the disintegration and cell death of F. solani. In addition, MXene nanoflakes could transport into roots through T. grandis root air space, which resulted in the accumulation of lignin in roots via enhancing the expression and activities of lignin biosynthesis-related genes in T. grandis roots. Taken together, our finding pioneers comprehensive insights into the antifungal mechanism of MXene against F. solani and the efficiency use of MXene in protecting plant against pathogenic fungus, which will prompt the rapid development of nanotechnology in sustainable forestry.