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Abstract Seed triacylglycerol (TAG), a major component of vegetable oil, consists of a glycerol esterified with three fatty acids. Vegetable oil has industrial applications and is widely used as edible oil. The increasing demand for plant oils, owing to population growth, it is crucial to enhance the oil content in seeds. We found castor WRINKLED1A (RcWRI1A) and R2R3-type MYB domain protein 306 (RcMYB306) which have homology with Arabidopsis WRI1 (AtWRI1) and AtMYB96 which regulate genes involved in fatty acid and TAG synthesis, respectively. These castor genes were separately and jointly overexpressed using seed-specific promoters in an oil crop, camelina (Camelina sativa). Overexpression of RcWRI1A, RcMYB306, or RcWRI1A + RcMYB306 increased the total seed oil content in camelina. However, this increase was not significantly different from that observed during the overexpression of RcWRI1A or/and RcMYB306. RcWRI1A overexpression increased the fatty acid content, including 16:0, 18:2, 18:3. Contrastingly, RcMYB306 overexpression increased the 18:1, 18:2, 18:3, 20:0 and 20:1 fatty acid. In the RcWRI1A + RcMYB306 lines, changes in fatty acid composition demonstrated the combined effects of these transcription factors. These results suggest that RcWRI1A and RcMYB306 can be used to improve the productivity of oil crops.

Suberin, a complex polyester deposited in the seed coat outer integument, acts as a hydrophobic barrier to control the movement of water, ions, and gas. However, relatively little is known about the signal transduction involved in suberin layer formation during seed coat development. In this study, the effect of the plant hormone abscisic acid (ABA) on suberin layer formation in seed coats was investigated by characterizing mutations in Arabidopsis related to ABA biosynthesis and signaling. Seed coat permeability to tetrazolium salt was noticeably elevated in aba1-1 and abi1-1 mutants, but not significantly altered in snrk2.2/3/6, abi3-8, abi5-7, and pyr1pyl1pyl2pyl4 quadruple mutants compared with that in the wild-type (WT). ABA1 encodes a zeaxanthin epoxidase that functions in the first step of ABA biosynthesis. aba1-1 and aba1-8 mutant seed coats showed reduced autofluorescence under UV light and increased tetrazolium salt permeability relative to WT levels. ABA1 disruption resulted in decreased total seed coat polyester levels by approximately 3%, with a remarkable reduction in levels of C24:0 ω-hydroxy fatty acids and C24:0 dicarboxylic acids, which are the most abundant aliphatic compounds in seed coat suberin. Consistent with suberin polyester chemical analysis, RT-qPCR analysis showed a significant reduction in transcript levels of KCS17, FAR1, FAR4, FAR5, CYP86A1, CYP86B1, ASFT, GPAT5, LTPG1, LTPG15, ABCG2, ABCG6, ABCG20, ABCG23, MYB9, and MYB107, which are involved in suberin accumulation and regulation in developing aba1-1 and aba1-8 siliques, as compared with WT levels. Together, seed coat suberization is mediated by ABA and partially processed through canonical ABA signaling.

Vegetable oils are indispensable in human and animal diets and have been widely used for the production of detergents, lubricants, cosmetics, and biofuels. The seeds of an allotetraploid Perilla frutescens contain approximately 35 to 40% oils with high levels of polyunsaturated fatty acids (PUFAs). WRINKELD1 (WRI1) encoding an AP2/ERF-type transcription factor is known to upregulate the expression of genes involved in glycolysis and fatty acid biosynthesis and TAG assembly. In this study, two WRI1 isoforms, PfWRI1A, and PfWRI1B were isolated from Perilla and predominantly expressed in developing Perilla seeds. The fluorescent signals from PfWRI1A:eYFP and PfWRI1B:eYFP driven by the CaMV 35S promoter were detected in the nucleus of the Nicotiana benthamiana leaf epidermis. Ectopic expression of each of PfWRI1A and PfWRI1B increased the levels of TAG by approximately 2.9- and 2.7-fold in N. benthamiana leaves and particularly, the enhanced levels (mol%) of C18:2, and C18:3 in the TAGs were prominent with the concomitant reduction in the amounts of saturated fatty acids. The expression levels of NbPl-PKβ1, NbKAS1, and NbFATA, which were known to be target genes of WRI1, significantly increased in tobacco leaves overexpressing PfWRI1A or PfWRI1B. Therefore, newly characterized PfWRI1A and PfWRI1B can be potentially useful for the enhanced accumulation of storage oils with increased PUFAs in oilseed crops.