Whole-plant spatiotemporal responses to salinity reveal osmotic and ionic drivers of salt tolerance in broccoli

BACKGROUND: Soil salinity is a critical threat to global agriculture and understanding the dynamic and tissue-specific responses of crops exposed to salt is essential for developing mitigation strategies. Broccoli (Brassica oleracea L. var. italica), a crop that shows sensitivity to salinity while retaining the ability to activate adaptive responses, has not been extensively studied at the molecular level under salinity. In this study, we conducted a time-course analysis combining transcriptomic, physiological, and biochemical approaches to unravel the mechanisms underlying the tolerance of broccoli to salt stress. RESULTS: A time-course analysis combining transcriptomics, physiology, and biochemistry revealed that broccoli employs a highly coordinated systemic strategy. First, osmotic adaptation was driven by rapid and sustained osmoprotection through P5CS activation and PDH1 repression, resulting in robust proline accumulation. Second, ionic stress responses were highly tissue-specific: leaves prioritized early K⁺ homeostasis, while roots acted as primary sensors, triggering early signalling and exclusion via the SOS1/SOS3.1 pathway, NHX1.1/NHX2 vacuolar sequestration, and a robust root-specific induction of the cation/H⁺ exchanger CHX20, highlighting a prioritized mechanism for pH and ionic homeostasis. Last, shoots showed oxidative stress responses via GSTU and AOX genes, complemented by mitochondrial protection in roots. Systemic coordination was further supported by altered hormone and phenylpropanoid profiles, reflected by the late-stage accumulation of chlorogenic acid in leaves to preserve photosynthetic function. This systemic coordination was supported by a complex hormonal redistribution of ABA, JA, and IAA in roots and early SA increases in shoots. Furthermore, salinity complexly regulated secondary metabolism; despite late-stage glucobrassicin declines in leaves, early transcriptomic activation of glucosinolate biosynthesis and differential GTR expression suggested enhanced glucosinolate turnover and redistribution under stress. CONCLUSIONS: Our results provide a comprehensive spatiotemporal map of the response of broccoli to salinity, highlighting key candidate genes and physiological traits associated with moderate salinity acclimation, providing a framework to explore strategies for sustaining productivity in saline environments.