As plants often alter their metabolism in response to viral infections, the mechanisms involved in this process remain a research hotspot. Here, we examined the leaf fatty acid (FA) content in cucumber plants and revealed significant changes in the composition of FAs before and after severe cucumber green mottle mosaic virus (CGMMV) infection. Before severe CGMMV infection, saturated FAs accumu lated, whereas unsaturated FAs decreased. Meanwhile, the opposite was observed after CGMMV infection. The expression and localization of the stearoyl-acyl-carrier protein desaturase 2 (CsSSI2), which is responsible for FA desaturation, were modulated upon CGMMV infection. The accumulation of both saturated FA substrates and unsaturated FA products resulting from CsSSI2 activity, as well as silencing of the CsSSI2 gene, hindered CGMMV infection. Furthermore, CsSSI2-mediated changes in FA composition affected the balance between jasmonic acid (JA) and salicylic acid (SA), favoring a shift from SA to JA biosynthesis during severe CGMMV infection, thereby contributing to the inhibition of CGMMV infection and its physical transmission. Overall, our study sheds novel insights into the mechanism whereby FA metabolism in cucumber plants adapts to counteract viral infection, expanding our understanding of plant–virus interactions and suggesting potential strategies for enhancing crop resistance to viral diseases.
