||Rapeseed(Brassica napus) is an important oilseed crop worldwide.Its silique length(SL) and seed weight(SW) are positively correlated with yield. Here, we isolated a rapeseed gene, DEFECTIVE IN ANTHER DEHISCENCE 1 (DAD1; Bna.A05DAD1), whose transgenic overexpression could significantly increase the SL of Arabidopsis thaliana. Bna.A05DAD1 is specifically expressed in the seeds and anthers, and its associated protein is localized to the chloroplast. The recombinant Bna.A05DAD1 protein had phospholipase enzymatic activity both in vitro and in vivo, and could degrade oleic acid to generate linoleic acid and linolenic acid. Compared with the wild type, the concentrations of linoleic acid and linoleic acid were increased in the DAD1-overexpressing rapeseed plants, indicating that Bna.A05DAD1 directly altered their fatty acid composition, an indirectly via the upregulation of FAD2 and FAD3. A transcriptomic comparison revealed that Bna.A05DAD1 overexpression mainly influenced the fatty acid biosynthesis and phytohormone response pathways. Moreover, SL and SW were significantly increased in both transgenic rapeseed and Arabidopsis plants, due to the enlargement of the silique pericarp cells. The overexpression of Bna.A05DAD1 resulted in the upregulation of jasmonic acid biosynthesis genes (Allene Oxide Cyclase 4, AOC4; Allene Oxide Synthase, AOS; and Oxophytodienoate-reductase 3, OPR),the repression of the well-known negative regulator of the auxin signaling pathway gene Auxin Response Factor 18 (Bna.A09ARF18), and the subsequent activation of the auxin-responsive genes, such as PIN-FORMED 1 (PIN1) and GRETCHEN HAGEN 3 (GH3), leading to the increase of SL and SW in rapeseed. Our results not only provide new insights into the roles of Bna.A05DAD1 in the regulation of the fatty acid composition and yield improvements through the crosstalk of the jasmonic acid and auxin signaling pathways, but also reveal an important genetic resource for the breeding of high-yielding rapeseed.