Phytohormone crosstalk governing root system plasticity in wheat under salinity stress

Soil salinity constrains wheat productivity by imposing simultaneous osmotic limitation, ionic imbalance, and oxidative stress, yet the mechanisms by which wheat roots convert these stress signals into adaptive or maladaptive developmental responses remain incompletely resolved. This review examines salinity-induced wheat root system plasticity through the lens of phytohormone crosstalk, focusing on how early stress signals are integrated with hormonal regulation to shape root elongation, branching, root hair development, and barrier-related remodeling. Rather than treating root plasticity as a descriptive morphological response, we evaluate it as an evidence-weighted signaling-to-function process that distinguishes the magnitude of plasticity from its adaptive value. Current evidence is assessed across four levels: direct wheat-root studies, broader wheat evidence, cereal-based inference, and model-plant extrapolation. This hierarchy indicates strong wheat-root support for brassinosteroid-auxin regulation of reversible developmental pausing, whereas abscisic acid-, ethylene-, and reactive oxygen species-associated responses show functional convergence but their integrated crosstalk remains incompletely resolved. Other hormone pathways remain more context-dependent or less well resolved. We propose a wheat-focused five-stage framework linking composite stress detection, early signal processing, hormonal network rebalancing, coordinated developmental execution, and functional filtering. The framework distinguishes visible plasticity from adaptive plasticity by requiring root traits to be evaluated against ion regulation, water relations, oxidative balance, recovery capacity, and plant performance under salinity. This synthesis argues that future wheat phenotyping and breeding should prioritize functionally validated traits, including preserved meristem viability, reversible branching competence, selective barrier remodeling, and post-stress recovery, rather than greater root growth alone.