The 13-lipoxygenase MSD2 and the ω-3 fatty acid desaturase MSD3 impact Spodoptera frugiperda resistance in Sorghum.

Linolenic acid produced by the ω-3 fatty acid desaturase MSD3 in sorghum is used for insect-induced jasmonic acid production and is important for resistance against Spodoptera frugiperda. Jasmonic acid (JA) is a phytohormone that regulates both plant development and stress responses. In sorghum (Sorghum bicolor), the ω-3 fatty acid desaturase Multiseeded3 (MSD3) and the 13-lipoxygenase Multiseeded2 (MSD2) are important for producing JA to regulate panicle development and spikelet fertility, but their function in plant defense remains unknown. In this study, we examined whether these genes are important for the production of JA in response to herbivory by the insect pest Spodoptera frugiperda. Compared to wild-type controls, the msd3 mutant accumulated less JA in leaves of both infested and uninfested plants, revealing that MSD3 is involved in stress-induced JA production. In contrast, herbivore-induced JA production in the msd2 mutant was indistinguishable from wild type, indicating that MSD2 does not function in herbivore-induced JA production. An increase of S. frugiperda growth was observed on both the msd3 and msd2 mutants, hinting at roles for both JA and additional oxylipins in sorghum's defense responses.