Indole-3-acetic acid promotes wound healing of potato tubers by activating auxin signaling and phenylpropanoid metabolism

IAA increased endogenous auxin levels during tuber wound healing. • Auxin signaling genes were upregulated by IAA treatment. • IAA activated phenylpropanoid pathway genes and enzymes. • Formation of protective barrier was enhanced under IAA treatment. • IAA reduced weight loss and disease index in wounded tubers. Indole-3-acetic acid (IAA) is a major endogenous auxin, yet its involvement in closing layer formation at potato tuber wounds is not well defined. In this study, potato tubers (cv. Atlantic) were treated with IAA (100 mg L⁻¹) or N-1-naphthylphthalamic acid (NPA) (100 mg L⁻¹) and stored for up to 21 d during wound-healing, with samples collected at multiple time points. Transcriptome analysis showed that differentially expressed genes were mainly enriched in plant hormone signal transduction and phenylpropanoid biosynthesis pathways. IAA treatment significantly increased endogenous IAA accumulation and upregulated auxin biosynthesis and signaling genes, including StTAR2 and StYUCCA50 , as well as downstream signaling components such as StIAA29 , StARF8 , StGH3.6 , and StSAUR50 . Transcriptome and biochemical analyses showed that IAA enhanced phenylpropanoid metabolism, as evidenced by increased expression and activities of key enzymes, including phenylalanine ammonia-lyase (PAL), cinnamate 4-hydroxylase (C4H), 4-coumarate-CoA ligase (4CL), and cinnamyl alcohol dehydrogenase (CAD). Correspondingly, IAA promoted the accumulation of phenolic acids (cinnamic acid, caffeic acid, ferulic acid, and p -coumaric acid), lignin monomers, and total lignin, along with enhanced deposition of suberin polyphenolics and lignified cell layers at wound sites. In contrast, NPA treatment generally suppressed auxin accumulation, phenylpropanoid metabolism, and barrier formation. These coordinated molecular and metabolic changes were associated with reduced weight loss and lower disease index during storage. Correlation analysis further indicated strong associations among auxin-related responses, phenylpropanoid metabolism, barrier deposition, and healing performance. Collectively, these findings demonstrate that auxin-associated regulation is closely linked to phenylpropanoid activation and closing layer formation during potato tuber wound healing.