Trehalose Promotes the Melon Seedlings Growth by Mediating Crosstalk of IAA and GA Signalling Pathways

Cold stress limits plant growth and development, delays transplanting and fruit marketing, and reduces economic returns. Exogenous trehalose (Tre) induces indole-3-acetic acid (IAA) synthesis and upregulates the IAA-responsive small auxin up RNA gene CmSAUR1, and thereby enhances cold tolerance in melon seedlings. Its role in growth regulation, however, remains unclear. In this study, exogenous Tre, IAA, and gibberellin (GA) significantly promoted stem internode cell expansion and elongation and increased plant biomass in melon seedlings. Inhibition of IAA signaling by N-1-naphthylphthalamic acid (NPA), an inhibitor of polar auxin transport, attenuated the effect of Tre but did not affect the effect of GA. In contrast, inhibition of GA biosynthesis by uniconazole, a GA biosynthesis inhibitor, abolished the effect of Tre and significantly weakened the effect of IAA. CmSAUR1, induced by IAA, negatively regulated melon seedling growth, whereas GA₃ treatment suppressed CmSAUR1 expression. These findings indicate that Tre promotes melon seedling growth under normal temperature conditions and after recovery from low-temperature stress by mediating IAA and GA signaling. Crosstalk occurs between the IAA and GA pathways, and GA may act downstream of IAA as a central component of Tre function. CmSAUR1 may integrate the interaction between GA and IAA signaling and participate in Tre-mediated growth regulation. The results of this study provide a theoretical reference for the application of Tre in melon cultivation and for further in-depth research on the interaction between IAA and GA signaling in regulating plant growth.