Jasmonate biosynthesis regulates key events in barley vegetative and reproductive development.

Cereal grain is a global food staple. Filial tissues in grain, such as the embryo and endosperm, grow embedded in the maternal ovule and surrounding ovary wall. Maternal tissues provide nutrition and protection but are progressively reduced and degraded as filial tissues expand, driving grain expansion between floret hulls. While we know some enzymatic players, regulation of this process remains less understood. However, our previous work in barley, Hordeum vulgare spp. vulgare suggested a role for the phytohormone jasmonate (JA). We edited the barley ALLENE OXIDASE CYCLASE (HvAOC) gene encoding a JA biosynthetic enzyme. We examined hvaoc mutants for developmental phenotypes, genetic interactions and effects on the transcriptome. Defective HvAOC alleles reduced JA levels, and caused enhanced vegetative growth, faster flowering and lengthened grain, all phenotypes rescued by MeJA treatment. HvAOC control of grain length appears parentally-derived, consistent with enriched HvAOC expression in maternal compared to filial tissues. Grain dimension changes were uncoupled from hull size and correlated with larger endosperm cavities, more persistent maternal tissues and higher expression of genes linked to sucrose transport. This work provides the first genetic dissection of JA in barley and highlights roles in coordinating maternal tissues within grain.