Spatial and development responses in the wheat leaf highlight the loss of chloroplast protein homeostasis during salt stress.

Salinity stress in wheat affects physiological and biochemical parameters in tissues that alter plant development and ultimately lower crop yield. Shoot tissues can accumulate high concentrations of sodium over time through the transpiration stream coming from the roots. This imposes physiological responses that align salt effects with the basipetal developmental gradient of the monocot leaf. The role of metabolic processes in generating and responding to these increases in sodium concentration over time was explored by linking changes in ion distributions to those of enzyme abundance from the base to the tip of leaves under salt stress. We found that enzymes for methionine synthesis and lipid degradation pathways increase, concomitantly with proteins in jasmonate synthesis, which are key players in plant stress-induced responses. Combining the use of Differential Abundance of Protein analysis and Weighted Correlation Network Analysis we have focused on identifying key protein hubs associated with responses to salt stress or salt susceptibility, shedding light on potential sites of salt sensitivity as targets for enhancing salt tolerance in wheat. We found chloroplast protein synthesis machinery, including the 30S and 50S ribosomal proteins, and plastid localised protein synthesis elongation factors, were significantly reduced in abundance and correlated with the altered K/Na ratio along salt-stressed wheat leaves. Additionally, the plastid protease system including ATP-dependent caseinolytic protease and filamentous temperature-sensitive H proteases involved in chloroplast protein homeostasis, show decreased abundance with salt. The complex interplay of these processes in and across the leaf affects overall plant viability under salt stress mainly affecting the energy homeostasis in wheat shoot. Data are available via ProteomeXchange with identifier PXD059765. SIGNIFICANCE: Soil salinity is a major agricultural challenge that cause significant reduction in wheat yields, a staple crop vital for global food security. Despite extensive breeding efforts, developing salt-tolerant wheat remains challenging due to the complex, multi-genic nature of salinity tolerance. While numerous studies have explored molecular responses to salt stress making salt to control comparisons, there is little consensus on the primary points of metabolic disruptions that would determine the salt response in wheat. Our study addresses this gap by integrating proteomics with Weighted Correlation Network Analysis to examine metabolic responses along the developmental gradient of wheat leaves. By exploiting the natural base-to-tip progression of leaf maturation under salt stress, we identify key protein groups linked to salt response. These findings provide new insights into potential metabolic targets for enhancing wheat's resilience to salinity stress.