The TgIAA7-TgARF10- <i>TgProDH1</i> module regulates waterlogging-mediated proline accumulation in the gymnosperm <i>Torreya grandis</i>

Waterlogging stress severely limits plant growth and development. Proline accumulation serves as a crucial adaptive mechanism in plants responding to waterlogging stress. However, the molecular mechanisms underlying waterlogging-mediated proline homeostasis in gymnosperm species have received limited attention to date. In this study, we demonstrated that the TgIAA7-TgARF10 module inhibited the expression of Proline Dehydrogenase 1 (TgProDH1) to modulate proline accumulation in response to waterlogging in Torreya grandis, a Jurassic-origin gymnosperm with a millennial economic lifespan and high ecological value in subtropical mountainous regions. Waterlogging stress downregulated the expression of TgProDH1-encoding a key enzyme gene in proline degradation-in T. grandis. TgProDH1 negatively regulated waterlogging-mediated proline accumulation in T. grandis. The ARF transcription factor TgARF10 inhibited TgProDH1 expression by directly binding to its promoter, and waterlogging stress enhanced the binding affinity of TgARF10 for the TgProDH1 promoter. Additionally, TgIAA7 interacted with TgARF10 in vivo and in vitro, significantly reducing the transcriptional repression activity of TgARF10 by inhibiting its DNA-binding ability, ultimately repressing waterlogging-induced proline accumulation. Our findings indicate that the TgIAA7-TgARF10 module finely tunes TgProDH1 expression to maintain waterlogging-mediated proline homeostasis in T. grandis. This study enhances our understanding of transcriptional regulation of proline accumulation in T. grandis under waterlogging stress and fills a critical knowledge gap in the regulatory mechanisms by which auxin modulates proline homeostasis in gymnosperms.