The plantacyanin gene family in tomato: genome-wide identification, expression analysis, and regulation of salt stress tolerance

Phytocyanins (PCs) are a class of plant-specific blue copper proteins that play critical roles in plant development and responses to environmental stresses. Although the PC gene family has been characterized in several plant species, it has not been systematically investigated in tomato, and its role in salt stress tolerance remains largely unknown. In this study, we identified 49 PC genes in tomato. Phylogenetic analysis clustered SlPC gene family into five distinct clades. Collinearity analysis within the SlPC gene family identified five collinear gene pairs. Interspecific collinearity analysis revealed 25 and 53 homologous gene pairs between tomato and Arabidopsis, and tomato and potato, respectively. Intron-exon structure analysis showed that only SlENODL6 is intronless. Promoter analysis indicated the presence of cis-elements associated with growth, development, hormone and stress responses. Expression profiling and qRT-PCR analysis showed that SlSC6 expression was induced by salt and abscisic acid treatments. Silencing SlSC6 resulted in reduced salt tolerance, evidenced by elevated malondialdehyde and proline content, increased relative electrolyte leakage, and inhibited root growth. Additionally, the transcript levels of SOS1, SOS2, DREB2A and CYP707A2 were significantly downregulated, while CYP707A1 was significantly upregulated in SlSC6-silenced lines. Silencing also impaired antioxidant enzyme activity and led to increased accumulation of reactive oxygen species (ROS) under salt stress. Overall, these findings suggest that SlSC6 plays a role in conferring salt stress tolerance in tomato. This study lays a foundation for future functional studies of SlPC genes and provides new insights into the molecular mechanisms underlying tomato salt stress tolerance.