Abstract
BackgroundSimmondsia chinensis (jojoba) is the only plant known to store wax esters instead of triacylglycerols in its seeds. Wax esters are composed of very-long-chain monounsaturated fatty acids and fatty alcohols and constitute up to 60% of the jojoba seed weight. During jojoba germination, the first step of wax ester mobilization is catalyzed by lipases. To date, none of the jojoba lipase-encoding genes have been cloned and characterized. In this study, we monitored mobilization of storage reserves during germination of jojoba seeds and performed detailed characterization of the jojoba lipases using microsomal fractions isolated from germinating seeds.ResultsDuring 26 days of germination, we observed a 60–70% decrease in wax ester content in the seeds, which was accompanied by the reduction of oleosin amounts and increase in glucose content. The activity of jojoba lipases in the seed microsomal fractions increased in the first 50 days of germination. The enzymes showed higher activity towards triacylglycerols than towards wax esters. The maximum lipase activity was observed at 60 °C and pH around 7 for triacylglycerols and 6.5–8 for wax esters. The enzyme efficiently hydrolyzed various wax esters containing saturated and unsaturated acyl and alcohol moieties. We also demonstrated that jojoba lipases possess wax ester-synthesizing activity when free fatty alcohols and different acyl donors, including triacylglycerols and free fatty acids, are used as substrates. For esterification reactions, the enzyme utilized both saturated and unsaturated fatty alcohols, with the preference towards long chain and very long chain compounds.ConclusionsIn in vitro assays, jojoba lipases catalyzed hydrolysis of triacylglycerols and different wax esters in a broad range of temperatures. In addition, the enzymes had the ability to synthesize wax esters in the backward reaction. Our data suggest that jojoba lipases may be more similar to other plant lipases than previously assumed.
Highlights
Simmondsia chinensis is the only plant known to store wax esters instead of triacylglycerols in its seeds
Mobilization of jojoba seed reserves during germination Jojoba seeds from four different accessions were germinated for a period of 26 days (Additional file 1: Fig. S1), and changes in wax ester content were monitored using GC-flame ionization detector (FID) analysis
Analysis of lipid classes in jojoba seeds from four accessions revealed that wax esters are predominant class of lipids (95–98%)
Summary
Simmondsia chinensis (jojoba) is the only plant known to store wax esters instead of triacylglycerols in its seeds. Wax esters are composed of very-long-chain monounsaturated fatty acids and fatty alcohols and constitute up to 60% of the jojoba seed weight. Jojoba (Simmondsia chinensis Link, Buxaceae) is a perennial shrub that grows naturally in the deserts of southwestern North America. It is the only known plant species which accumulates wax esters in the seeds as storage reserves instead of triacylglycerols. Wax esters constitute up to 60% of seed weight and are composed of very-long-chain monounsaturated fatty acids and alcohols, such as eicosenoic acid (20:1), docosenoic acid (22:1), eicosenol (20:1-OH) and docosenol (22:1-OH) [1, 2]. It was suggested that impaired wax ester degradation may be a bottleneck for seed viability in high-wax esters accumulating plants [18]
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