Modulation of SAL Retrograde Signalling Promotes Yield and Water Productivity Responses in Dynamic Field Environments.

Chloroplast-to-nucleus retrograde signalling enables rapid stress responses in plants, but whether these signals accumulate to affect crop performance across entire growing seasons under field conditions remains unknown. We generated wheat mutants with targeted deletions in specific SAL gene copies from two distinct homeologous groups (TaSAL1 and TaSAL2), creating lines with enhanced stress signal responsiveness. We tested these lines across 15 field trials spanning diverse Australian environments with varying temperatures, rainfall, and irrigation regimes, measuring physiological responses, yield, biomass, and water productivity. Lines with TaSAL2 gene deletions showed 4-8% yield improvements with enhanced water productivity, while TaSAL1 deletions reduced yields. The TaSAL2 mutants maintained superior photosynthetic function under drought stress, showed improved relative water content, and demonstrated enhanced yield stability across environments. Canopy temperature measurements revealed dynamic stomatal regulation, with increased closure during midday stress periods but normal aperture under benign conditions. Significantly, specific SAL modifications enhanced photosynthetic efficiency and stress resilience without traditional yield penalties. Targeted modification of specific SAL homeologous groups can simultaneously improve both yield and stress tolerance in wheat. This demonstrates that retrograde signalling integrates environmental information across the plant lifecycle and highlights the importance of locus-specific targeting and multienvironment field validation for crop modifications.