Functional potential of the APETALA2 transcription factors StAP2-13/18 in modulating tuberization under long-day (LD)...

Tuberization represents the most critical biological process during the growth and development of potato (Solanum tuberosum L.), as it directly dictates the final yield and quality of the crop. The APETALA2 (AP2) family of transcription factors (TFs) serves as key regulators of plant development, orchestrating diverse processes including organogenesis, hormone signaling, and environmental adaptation. Nevertheless, the precise functions of StAP2 genes in potato tuberization remain elusive, limiting our understanding of the molecular regulatory network underlying this agriculturally important trait.

A total of 18 StAP2 genes, designated StAP2-1 to StAP2-18 according to their chromosomal positions in the potato genome, were identified. Herein, we present a comprehensive genome-wide systematic analysis of these StAP2 genes, encompassing their phylogenetic relationships, conserved motif characteristics, and tuberization-related expression profiles. Our expression data demonstrated that StAP2-13 and StAP2-18 are most likely involved in potato tuberization, as evidenced by their marked upregulation in tuberization-related leaves and developing tubers, respectively. In addition, both StAP2 genes exhibit distinct circadian rhythmic expression patterns - a regulatory feature known to modulate potato tuberization via crosstalk with photoperiod signaling. Yeast two-hybrid experiment verified that StAP2-13 and StAP2-18 physically interact with the key tuberization regulatory factor StCDF1. Furthermore, yeast one-hybrid experiment and dual-luciferase reporter assays confirmed that StAP2-13 and StAP2-18 directly bind to the promoter of the tuber-inducing gene StSP6A and activate its transcriptional activity. More importantly, transgenic overexpression of StAP2-13 or StAP2-18 markedly promoted tuber initiation in potato plants under long-day conditions, a non-favorable photoperiod for tuberization in most potato cultivars.

These results provide a comprehensive genome-wide characterization of the StAP2 gene family in potato, and identify StAP2-13 and StAP2-18 as promising candidate targets for genetic improvement of tuberization-related traits in potato, particularly for enhancing productivity under long-day growing environments.