Sorghum MSD3 Encodes an ω-3 Fatty Acid Desaturase that Increases Grain Number by Reducing Jasmonic Acid Levels

Grain number per panicle is an important component of grain yield in sorghum ( (L.)) and other cereal crops. Previously, we reported that mutations in multi-seeded 1 ( and genes result in a two-fold increase in grain number per panicle due to the restoration of the fertility of the pedicellate spikelets, which invariably abort in natural sorghum accessions. Here, we report the identification of another gene, which is also involved in the regulation of grain numbers in sorghum. Four bulked F populations from crosses between BTx623 and each of the independent mutants p6, p14, p21, and p24 were sequenced to 20× coverage of the whole genome on a HiSeq 2000 system. Bioinformatic analyses of the sequence data showed that one gene, Sorbi_3001G407600, harbored homozygous mutations in all four populations. This gene encodes a plastidial ω-3 fatty acid desaturase that catalyzes the conversion of linoleic acid (18:2) to linolenic acid (18:3), a substrate for jasmonic acid (JA) biosynthesis. The mutants had reduced levels of linolenic acid in both leaves and developing panicles that in turn decreased the levels of JA. Furthermore, the panicle phenotype was reversed by treatment with methyl-JA (MeJA). Our characterization of and now demonstrates that JA-regulated processes are critical to the phenotype. The identification of the gene reveals a new target that could be manipulated to increase grain number per panicle in sorghum, and potentially other cereal crops, through the genomic editing of functional orthologs.