Disruption of Fatty Acid Desaturase Gene Alters Aphid Resistance and Volatile Emissions in Sorghum

Jasmonic acid (JA)-deficient msd3 sorghum mutants exhibit contrasting resistance phenotypes against sugarcane aphids (SCA; Melanaphis sacchari), which promotes aphid settling at early time points while providing antibiosis-mediated resistance at later stages. Here we investigated the physiological, hormonal, and metabolic mechanisms underlying msd3-mediated resistance to SCA. Contrary to the widely reported growth-defence trade-off, msd3 plants maintained biomass comparable to uninfested controls, while wild-type (WT) plants showed significant reduction in biomass following SCA feeding. Gas exchange measurements and stomatal imaging revealed that SCA infestation elevated stomatal conductance and transpiration in WT but not msd3 plants, a response associated with a concurrent drop in abscisic acid levels in WT plants. Notably, the tighter stomatal regulation observed in msd3 plants may simultaneously contribute to direct defence while limiting foliar volatile emissions, a finding supported by the significantly reduced total volatile emission in msd3 plants following SCA infestation. Furthermore, msd3 plants exhibited elevated levels of free amino acids and defence-related secondary metabolites. Collectively, these findings demonstrate that loss of MSD3 function reshapes the sorghum defence landscape, enhancing direct defence while reducing volatile emissions linked to indirect defence. Stomatal regulation is associated with both responses, though a mechanistic connection between them remains to be established.