StHY5 activates StSP6A to control photoperiod-induced tuberization in potato

Photoperiod critically regulates potato tuber development, with short days inducing the expression of the key tuberigen signal, SELF PRUNING 6A (StSP6A). To identify upstream regulators of StSP6A, we performed a transcriptome analysis of potato leaves in response to short days. Among the short day-responsive genes identified, ELONGATED HYPOCOTYL 5 (StHY5) emerged as a strong candidate regulator. We demonstrated that StHY5 expression is rapidly modulated in response to photoperiodic changes and that it directly activates StSP6A transcription by binding to multiple ACGT-containing element motifs within its promoter. Functional validation revealed that overexpression of StHY5 significantly promotes tuber formation and yield, mirroring the effect of elevated StSP6A. These findings establish StHY5 as a critical photoperiodic signal transducer in potato, acting upstream of StSP6A to initiate and enhance tuber formation in response to inductive short days. This molecular pathway presents a potential target for optimizing tuber yield in potato breeding programs.