StSAUR31 functions as a negative regulator of enzymatic browning in potato ( Solanum tuberosum L.)

Abstract Enzymatic browning significantly affects the processing and quality maintenance of a wide range of horticultural produce. Identifying key regulators of browning is essential for elucidating its underlying mechanisms and developing effective mitigation strategies. In this study, transcriptomic comparison between potato cultivars with contrasting browning sensitivities identified a small auxin-up RNA, StSAUR31, as a potential regulator of auxin-mediated browning inhibition in potato. Functional analyses showed that overexpression of StSAUR31 markedly reduced browning intensity and PPO activity, whereas knockout of StSAUR31 produced the opposite phenotype. Correspondingly, StuPPO1 protein abundance decreased in StSAUR31 overexpression lines and increased in knockout lines. Mechanistically, StSAUR31 physically interacted with StuPPO1 in an auxin-enhanced manner, partially altering its subcellular localization and reducing its accumulation in plastids. Additionally, StSAUR31 downregulated StuPPO1 expression, reduced endogenous free tyrosine levels, and enhanced antioxidant capacity. Collectively, these findings indicated that StSAUR31 coordinately regulated PPO activity, substrate availability, and antioxidant capacity, thereby integrating multiple mechanisms to suppress enzymatic browning in potatoes. These results advance our understanding of the crosstalk between auxin signaling and enzymatic browning, providing new insights into the role of hormone signaling in postharvest quality regulation.