Sorbitol Reduces Sensitivity to Alternaria by Promoting Ceramide Kinases (CERK) Expression through Transcription Factor Pswrky25 in Populus (Populus simonii Carr.)

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.