Genome-Wide Identification and Functional Characterization of the Phytochelatin Synthase (PCS) Gene Family in Potato Reveals StPCS1′s Role in Cadmium Tolerance

Phytochelatin synthase (PCS) is crucial for synthesizing phytochelatins, cysteine-rich peptides vital for heavy metal detoxification in plants. Potato, a key staple crop in China, faces risks from soil heavy metal contamination, yet the genes involved in its detoxification, particularly PCS genes, remain underexplored. This study systematically identified and characterized the StPCS gene family in potato using genomic databases, uncovering five StPCS members distributed across three of the 12 potato chromosomes. Phylogenetic analysis classified StPCS proteins into three clades, while gene structure and motif analyses revealed high conservation in domain organization. Promoter region investigations identified stress-responsive elements in nearly all StPCS genes. Under cadmium (Cd) stress conditions, qPCR analysis indicated a significant upregulation of StPCS1 (5.73-fold) and StPCS2 (1.61-fold) transcript levels after 21 days compared to the control, whereas no obvious differences were observed at 7 days post-stress. Subsequent functional verification in yeast revealed that StPCS1 overexpression markedly improved Cd tolerance in transgenic yeast. In addition, analysis of cis-acting elements in the StPCS gene promoter combined with qPCR verification under MeJA and ABA stress conditions suggested that StPCS1 might be involved in Cd stress responses in potato through certain hormone signaling pathways. This study represents the first comprehensive analysis of the StPCS gene family in potato, clarifying its structural characteristics and characterizing the function of StPCS1 as a long-term Cd stress-responsive gene, which lays a solid foundation for investigating its role in heavy metal detoxification.