Integrated Metabolomic and Proteomic Analyses of Adventitious Rooting in Cucumis melo Under Waterlogging Stress

Waterlogging-induced hypoxic stress severely impairs vegetative growth and crop yield of melon (Cucumis melo L.). The formation of adventitious roots represents a critical morphological adaptive strategy for melon seedlings to alleviate hypoxic damage and maintain viability under waterlogging conditions. Nevertheless, the synergistic molecular regulatory mechanisms governing waterlogging-triggered adventitious root development in melon remain largely uncharacterized at the proteomic and metabolomic layers. In this study, the waterlogging-tolerant melon line 'L8' with superior adventitious root production capacity was exposed to waterlogging treatment, and hypocotyl tissues were harvested at 0, 24, 48 and 72 h post-waterlogging for untargeted metabolomic and proteomic analyses. A total of 1337 differentially accumulated metabolites (DAMs) and 2898 differentially expressed proteins (DEPs) were identified across the pairwise comparisons. Functional enrichment analyses of DAMs and DEPs indicated that pathways related to linoleic acid metabolism, α-linolenic acid metabolism, phenylpropanoid biosynthesis, biosynthesis of secondary metabolites, and glutathione metabolism were centrally implicated in adventitious rooting induced by waterlogging. At the protein level, pivotal functional proteins associated with anaerobic respiration (pyruvate decarboxylase, alcohol dehydrogenase), ethylene biosynthesis (1-aminocyclopropane-1-carboxylate oxidase), cell wall remodeling and antioxidant defense were significantly up-regulated throughout adventitious root development. In addition, three transcription factors, namely the GRAS family protein MELO3C025904.1, MYB-related protein MELO3C007640.1, and ZF-HD protein MELO3C022921.1, exhibited differential expression across different time points compared to the control. Moreover, metabolomic profiling identified three prominent metabolites with regulatory functions, encompassing the terpenoid acorusnol, the piperidine alkaloid 1,4'-bipiperidine-1'-carboxylic acid, and the flavonoid 4',7-dihydroxy-2'-methoxy-3'-prenylisoflavan. Omics correlation analysis revealed extensive concordance between metabolomic and proteomic profiles. Nine core DAMs, including N-methylserotonin, Val-Val and glyuranolide, were tightly correlated with hundreds of DEPs and key transcription factors, constructing a complex regulatory network governing waterlogging stress acclimation and adventitious root morphogenesis. This study systematically characterizes the coordinated proteomic and metabolomic reprogramming underlying waterlogging-induced adventitious root formation in melon. These findings deepen our understanding of the molecular mechanism of waterlogging tolerance and provide valuable candidate genes and metabolic targets for genetic improvement of waterlogging resistance in melon.