Potato (Solanum tuberosum L.) is the fourth largest food crop in the world. Low temperatures cause serious damage to potato plants every year, and freezing tolerance has become a hot spot in potato research. Galactinol synthase (GolS) is a key enzyme in the synthesis of raffinose family oligosaccharides (RFOs), and plays an important role in the response of plants to abiotic stress. In this study, the ScGolS1 gene from Solanum commersonii was cloned and introduced into the S. tuberosum cultivars ‘Atlantic’ and ‘Desiree’ via Agrobacterium-mediated transformation. Phenotyping assays showed that overexpression of ScGolS1 could significantly improve freezing tolerance in transgenic potato plants. Further physiological and biochemical experiments showed that the transgenic lines had lower relative conductivity, malondialdehyde content, and 3,3′-diaminobenzidine staining and a higher plant survival rate compared with wild type (WT) under cold stress. Moreover, the C-repeat binding factors (CBF1, CBF2 and CBF3), the downstream cold-responsive genes COR413 and COR47, and the ethylene-responsive factor (ERF) transcription factor genes ERF3, ERF4 and ERF6, which function in the ethylene signaling pathway, were all induced by freezing treatment and expressed at higher levels in the ScGolS1 overexpression lines compared with WT. Besides, the expression of some genes such as MIPS, STS and RS from the RFO metabolic pathway was up-regulated under cold stress, resulting in changes in the content of some soluble sugars. This indicated that ScGolS1 overexpression altered the sugar composition and enhanced freezing tolerance in transgenic potato by inducing the ethylene and CBF signaling pathways. These results provided theoretical support and genetic resources for freezing tolerance breeding in potato.

In order to elucidate the contributions of JA in orchestrating disease resistance in potato plants, the potato genotype 'SD20', which exhibits strong resistance against the highly virulent Phytophthora infestans isolate CN152, while infected by the super virulent isolate 2013-18-306, was treated with exogenous JA and then challenged by inoculation with 2013-18-306. The results showed that exogenously applied JA significantly delayed the onset and alleviated the symptoms of late blight, indicating exogenous JA could induce resistance to P. infestans in the early biotrophic stage of infection in 'SD20' plants. To further clarify the role of JA in the early defense response and identify key genes involved in JA signal transduction, gene expression profiling via RNA sequencing (RNA-seq) in 'SD20' plants treated with exogenously applied JA was performed. A total of 2927 differentially expressed genes were specifically induced, the majority encoded transcription factors, protein kinases, secondary metabolites, defense enzymes and disease resistance related proteins. GO functional annotation and KEGG metabolic pathway analysis showed that exogenously applied JA rapidly induced the expression of genes related to immune response regulation, pathogen defense, and other biological processes, and stimulated endogenous JA synthesis and signal transduction, and the overall early pathogen defense response in 'SD20'. These results provide useful information in understanding the JA's function involved in pathogen defense responses and a theoretical basis for the application of JA in potato production.

Salicylic acid (SA) is an important signaling substance that plays an important role in plant growth, development and disease resistance. In order to further understand the role of the SA pathway in potato disease resistance and identify SA signaling key genes, gene expression profiling of the late blight resistance genotype SD20 was performed under exogenous SA application. A total of 28572 unigenes were assembled, of which 4564 were differentially expressed. Analysis of differentially expressed genes (DEGs) showed that multiple signaling pathways such as SA, jasmonic acid, ethylene, abscisic acid, auxin, and brassinolide were involved in response to exogenous SA. Many plant defense signal-related genes involved in protein serine/threonine kinase activity and plant-pathogen interaction, were significantly enriched. These were consistent with the interaction results of SD20 and Phytophthora infestans in our previous study, indicating that exogenous SA stimulated the resistance response and initiated a similar defense pathway compared to pathogen infection in SD20, which confirmed crosstalk of the SA signaling pathway with a pathogen-induced disease resistance signal pathway in plant. Moreover, transcriptome analysis revealed that ROS1 was positively regulated by SA in potato for the first time. SA-induced gene expression profiling provides insight into SA signaling and its mechanisms in disease defense systems.