Timing Determines Fate: Temporal Dynamics of Jasmonate Signaling Distinguish Adaptive from Maladaptive Salt Stress Responses in Rice

Abstract

Plant encounters with saline conditions trigger a phase of osmotic stress, followed by ionic stress as salt accumulates in plant tissue. Jasmonate (JA) signalling plays a vital role in both phases, but its role for adaptation depends on timing. Using wild-type rice (Oryza sativa L. cv. Kitaake) and a JA-deficient allene oxide cyclase (aoc) mutant, we followed whole-plant physiology (growth, biomass, photosynthesis, ion distribution) with expression analysis for genes of jasmonate signalling, ion transporters and redox balance to separate adaptive from maladaptive JA effects. The aoc mutant sustained shoot and root growth more effectively than the wild type, maintaining cell expansion in the shoot and cell proliferation in the root under saline conditions. Likewise, stomatal conductance in the mutant was more persistent under salinity, accompanied by improved shoot K/Na homeostasis and reduced sodium in young leaves. In the wild-type, prolonged saline conditions were linked with induction of OsJAZ13 and OsNHX1, stomatal closure and chlorophyll degradation. We discuss these findings in the context of a model, where the function of JA signalling does not merely depend on its accumulation, but on its temporal dynamics. Here, OsHAK16 emerges as a marker of early adaptive responses, whereas OsNHX1 and OsJAZ13 characterize later maladaptive stress states, emphasising the potential of modulating JA dynamics to improve salt resilience in rice breeding.