WRINKLED1 Positively Regulates Oil Biosynthesis in Carya cathayensis

Hickory (Carya cathayensis Sarg.) is a kind of important woody oil tree species, and its nut has high nutritional value. Previous gene coexpression analysis showed that WRINKLED1 (WRI1) may be a core regulator during embryo oil accumulation in hickory. However, its specific regulatory mechanism on hickory oil biosynthesis has not been investigated. Herein, two hickory orthologs of WRI1 (CcWRI1A and CcWRI1B) containing two AP2 domains with AW-box binding sites and three intrinsically disordered regions (IDRs) but lacking the PEST motif in the C-terminus were characterized. They are nucleus-located and have self-activated ability. The expression of these two genes was tissue-specific and relatively high in the developing embryo. Notably, CcWRI1A and CcWRI1B can restore the low oil content, shrinkage phenotype, composition of fatty acid, and expression of oil biosynthesis pathway genes of Arabidopsis wri1-1 mutant seeds. Additionally, CcWRI1A/B were shown to modulate the expression of some fatty acid biosynthesis genes in the transient expression system of nonseed tissues. Transcriptional activation analysis further indicated that CcWRI1s directly activated the expression of SUCROSE SYNTHASE2 (SUS2), PYRUVATE KINASE β SUBUNIT 1 (PKP-β1), and BIOTIN CARBOXYL CARRIER PROTEIN2 (BCCP2) involved in oil biosynthesis. These results suggest that CcWRI1s can promote oil synthesis by upregulating some late glycolysis- and fatty acid biosynthesis-related genes. This work reveals the positive function of CcWRI1s in oil accumulation and provides a potential target for improving plant oil by bioengineering technology.