Germplasm Screening and Transcriptome Profiling Identify Phenylpropanoid Biosynthesis-Related PAL Candidate Genes Associated with Freezing Tolerance in Potato

Potato (Solanum tuberosum L.) seedlings are highly sensitive to freezing temperatures, which severely impairs growth and causes substantial losses in tuber yield and quality. This study aimed to screen freezing-tolerant potato germplasm accessions, identify candidate genes involved in the freezing response, and provide elite parental materials and a theoretical reference for molecular breeding of freezing-tolerant cultivars. We evaluated seedling freezing tolerance of 73 potato accessions using the freezing damage index (FDI), and performed transcriptome sequencing on leaf samples from highly freezing-tolerant (HT) accession 15-1881 and highly freezing-susceptible (HS) accession B8 following freezing treatment. Substantial variation in freezing tolerance was observed across the germplasm panel, with 5 HT accessions and 12 HS accessions identified, showing marked phenotypic and physiological differences under freezing stress. Transcriptomic analysis detected 6560 differentially expressed genes (DEGs) in 15-1881 and 5161 DEGs in B8, with 3558 DEGs specific to 15-1881. The phenylpropanoid biosynthesis pathway exhibited noticeable expression divergence between 15-1881 and B8, harboring 17 15-1881-specific DEGs including three tandem phenylalanine ammonia-lyase (PAL) genes. The HT germplasm accessions obtained in this study provide breeding resources for freezing-tolerant potato improvement, and the PAL genes characterized here represent promising candidate genes associated with freezing response in potato.