Xyloglucan represents the primary hemicellulose component in higher plant cell walls, providing mechanical support. The XTH gene family encodes xyloglucan endotransferase/hydrolase, a crucial enzyme in cell wall remodeling. Studies examining XTH family-related genes in apples remain limited. This study investigated the MdXTH30 gene, isolated from apple (Malus×domestica), which demonstrated responsiveness to abscisic acid, NaCl, and polyethylene glycol (PEG) 6000, with cytoplasmic localization confirmed through subcellular mapping. To elucidate the role of MdXTH30 in stress response, transgenic MdXTH30 apple calli were generated and the gene was heterologously expressed in Arabidopsis via Agrobacterium-mediated transformation. The findings revealed that MdXTH30 enhanced resistance to drought, salt stress, and pathogens through regulation of relevant genes in both apple calli and Arabidopsis. These results identify potentially significant candidate genes for improving biotic and abiotic stress resistance at the cell wall level.

China accounts for about half of the world's apple area and production, and is a pillar industry that promotes farmers' income growth and rural revitalization. In recent years, with the dramatic change of the global climate, most apple (Malus domestica) producing areas in China have suffered salt damage. Soil salinization, especially secondary salinization, is common in apple producing areas in the North China Plain around the Bohai Sea. These phenomena indicate that the ability of apple industry to prevent and resist soil salinization still needs to be improved. In this article, we identified a novel salt sensitive gene MdGPCR in apple. We conducted salt stress experiments on apple callus and leaves using MdGPCR. The results showed that after salt stress, overexpression of MdGPCR in transgenic apple would accumulate a large amount of reactive oxygen species, leading to an imbalance of redox levels in their bodies. At the same time, MdGPCR interacts with MdSOS3 and promotes its degradation, further reducing its salt stress resistance.

Abiotic stress has a serious effect on plant growth. The transcription factor DREB2A is a member of the AP2/ERF family, which is widely involved in abiotic stress response. However, the function of apple MdDREB2A has not been systematically investigated. In this study, MdDREB2A was isolated from the cultivar ‘Royal Gala’. The open reading frame of MdDREB2A was 1197 bp in length and it encoded a protein of 398 amino acids with molecular weight of 43.8 kD. As a transcription factor, MdDREB2A was located in the nucleus. qRT-PCR analysis showed that MdDREB2A was involved in responses to drought, salt, and ABA stresses. Under these stress treatments, the relative electrical conductivity, superoxide anion and malondialdehyde (MDA) in transgenic materials significantly decreased, and the content of proline increased in MdDREB2A transgenic plants, compared to the controls, indicating that MdDREB2A transgenic apple calli and transgenic Arabidopsis exhibited improved resistance to abiotic stress. This study introduces a candidate gene for the genetic improvement of crop resistance and reveals important function of MdDREB2A in the regulation of abiotic stress response.

Plant cuticular wax is an important determinant factor of fruit quality. Cuticular wax can protect the fruit from UV radiation, drought, and disease and increase the storage period of fruit. In many species, CER gene is associated with wax and can affect plant response to stress, but no characterization of CER gene and its family has been reported in apples. In this study, we identified 10 MdCER genes in Malus domestica based on the sequences of 10 CER genes in Arabidopsis thaliana. Three-dimensional structures were then defined, and root-mean-square deviation (RMSD) scoring matrixes were used to evaluate the matches. These 10 genes were divided into three classes using phylogenetic methods; namely, class I, II, and III. The predicted MdCER genes were distributed across 7 out of 17 chromosomes with different densities. Furthermore, the gene structures and motif compositions of the MdCER genes were analyzed. The quantitative real-time PCR results indicated that MdCER family genes were mainly expressed in the leaves and stems and rarely in the roots. Most of the MdCER members responded to salicylic acid and polyethylene glycol treatment, indicating that the MdCER family is associated with disease resistance (biotic) and abiotic stress.