| Summary: | Flax (<i>Linum usitatissimum</i> L.), as an important oil-producing crop, is widely distributed throughout the world, and its seeds are rich in polyunsaturated fatty acids (FAs). Previous studies have revealed that <i>Arabidopsis thaliana</i> ACETYL-CoA CARBOXYLASE (AtACCase) is vital for FA biosynthesis. However, the functions of <i>L. usitatissimum AccD</i> (<i>LuAccD</i>) on FA accumulation and seed germination remain unclear. In the present study, we cloned the LuAccD coding sequence from the flax cultivar ‘Longya 10’, identified conserved protein domains, and performed a phylogenetic analysis to elucidate its relationship with homologs from a range of plant species. Ectopic expression of <i>LuAccD</i> in <i>A. thaliana</i> wild-type background enhanced seed FA accumulation without altering seed morphological characteristics, including seed size, 1000-seed weight, and seed coat color. Consistently, the expression of key genes involved in FA biosynthesis was greatly up-regulated in the developing seeds of <i>LuAccD</i> overexpression lines. Additionally, we demonstrated that LuAccD acts as a positive regulator of salt and mannitol tolerance during seed germination in <i>A. thaliana</i>. These results provide important insights into the functions of <i>LuAccD</i>, which facilitates the oil quantity and abiotic stress tolerance of oil-producing crops through genetic manipulation.
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