Sugar, acting as a signal, can regulate the production of some chemical substance during plant defense responses. However, the molecular basis and regulatory mechanisms of sugar in poplar and other forest trees are still unclear. Sorbitol is a sugar-signaling molecule associated with plant defense. In this study, the pathogen-infested status of poplar was alleviated after exogenous feeding of 50 mM sorbitol. We sequenced and analyzed the transcriptome of poplar leaves before and after inoculation. The results showed that the genes PR1, WRKY, ceramide kinases (CERK) and so on responded to sorbitol feeding and pathogen infestation. We screened for genes related to disease resistance such as PsWRKY25 and PsCERK1 and found that significant disease spots occurred on day six of strep throat infestation. Under sorbitol feeding conditions, the appearance of spots was delayed after the pathogen inoculation. Due to the overexpression of PsWRKY25, the overexpression of PsCERK1 triggered the defense response in poplar. This was also confirmed by PsWRKY25 overexpression experiments. These findings present new insights into the influence of sorbitol on Populus simonii Carr. disease resistance. These results emphasize the value of molecular phenotypes in predicting physiological changes.

To investigate the effect of sorbitol feeding on immune responses and its underlying mechanism, this study employed crabapple (Malus micromalus), a species native to China, as the experimental material. Detached leaves were subjected to sorbitol feeding experiments, with water feeding as the control. The dynamic changes in lesion area and cell membrane permeability were measured across four groups of leaves following feeding and fungal inoculation, and transcriptome sequencing was performed on these four groups. The results revealed that compared to the control group, leaves fed with sorbitol prior to inoculation exhibited significantly reduced lesion areas and decreased cell membrane permeability. Transcriptome and KEGG pathway analyses indicated that differentially expressed genes were significantly enriched in the phenylpropanoid biosynthesis pathway. HPLC results demonstrated that quercetin and isorhamnetin contents increased significantly after sorbitol feeding, and both compounds were shown to inhibit the mycelial growth of Alternaria alternata, thereby enhancing the disease resistance of crabapple leaves. Among the associated genes, MmF3H1, which regulates the synthesis of quercetin and isorhamnetin, showed the highest level of enrichment. Co-expression trend analysis and qPCR results revealed that MmNAC17 and MmbZIP1 exhibited strong co-expression relationships with MmF3H1 and responded to sorbitol regulation. Functional validation was conducted by constructing overexpression and silencing vectors for MmNAC17/MmbZIP1 and performing transient transformation, thereby elucidating the molecular and biochemical mechanisms underlying the response of M. micromalus to A. alternata. This study provides a theoretical reference for breeding crabapple varieties with enhanced resistance to leaf spot disease.