Plant Developmental Reprogramming by Hymenopteran Gall Wasps: From Biochemical Signals to Molecular Mechanisms

Gall induction by hymenopteran gall wasps is one of the most sophisticated forms of plant-insect interaction, in which insects manipulate plant development to produce specialized, nutrient-rich structures that support their growth and reproduction. Despite substantial advances, the biochemical and molecular mechanisms underlying gall formation remain incompletely understood. This review synthesizes current knowledge on gall induction, focusing insect-derived signals, phytohormonal regulation, host developmental reprogramming, nutrient manipulation, and defense modulation. Evidence from physiological, transcriptomic, proteomic, and metabolomic studies indicates that gall development involves extensive reprogramming of host cellular, developmental, metabolic, and defense-related pathways. Altered auxin and cytokinin dynamics are associated with abnormal cell proliferation, tissue differentiation, vascular reorganization, and nutrient sink establishment, while gall-inducing wasps modulate host defenses through changes in oxidative signaling, secondary metabolism, and gene expression. Host genotype influences gall outcomes, with resistant plants exhibiting stronger defenses and restricted gall development. Collectively, available evidence suggests that gall formation results from the coordinated interaction of developmental, hormonal, metabolic, and defense-related processes. However, candidate insect-derived effectors may trigger phytohormonal alterations, nutrient sink formation, and defense modulation, collectively contributing to the reprogramming of host tissues into specialized organs that support insect development. Future multi-omics and functional studies are needed to identify key drivers of gall induction and host manipulation.