Genome-Wide Identification and Expression Analysis of the WOX Gene Family in Pepino (Solanum muricatum), Followed by Cloning and Subcellular Localization of SmWOX5 and SmWOX15.

WOX transcription factors play conserved roles in plant adventitious root development, but the WOX family in pepino (Solanum muricatum) has not been systematically characterized. To investigate this family, genome-wide identification and expression analysis were performed. A total of 15 SmWOX genes were identified, unevenly distributed across 12 chromosomes and phylogenetically divided into three clades: WUS (11), Intermediate (3), and Ancient (1). RT-qPCR revealed that most SmWOX genes showed the highest expression in apical buds and the lowest in leaves; among them, SmWOX5 and SmWOX15 exhibited significantly higher expression in roots. These two genes were subsequently cloned and subjected to subcellular localization analysis. SmWOX5 (492 bp, 163 amino acids) and SmWOX15 (2514 bp, 837 amino acids) were both predicted as non-transmembrane, non-secretory proteins, with differences in phosphorylation site distribution and structural conformations. Subcellular localization showed that SmWOX5 is exclusively nuclear, whereas SmWOX15 is predominantly nuclear with partial plasma membrane distribution. The WOX family in pepino exhibits evolutionary conservation with signs of functional divergence. The high root expression and differential localization of SmWOX5 and SmWOX15 suggest their distinct regulatory roles in root development and adventitious root formation, providing candidate genes for improving cutting propagation efficiency in pepino (Solanum muricatum).