Plant surface lipid biosynthetic pathways and their utility for metabolic engineering of waxes and hydrocarbon biofuels

Abstract

SummaryDue to their unique physical properties, waxes are high-value materials that are used in a variety of industrial applications. They are generated by chemical synthesis, extracted from fossil sources, or harvested from a small number of plant and animal species. As a result, the diversity of chemical structures in commercial waxes is low and so are their yields. These limitations can be overcome by engineering of wax biosynthetic pathways in the seeds of high-yielding oil crops to produce designer waxes for specific industrial end uses. In this review, we first summarize the current knowledge regarding the genes and enzymes generating the chemical diversity of cuticular waxes that accumulate at the surfaces of primary plant organs. We then consider the potential of cuticle biosynthetic genes for biotechnological wax production, focusing on selected examples of wax ester chain lengths and isomers. Finally, we discuss the genes/enzymes of cuticular alkane biosynthesis and their potential in future metabolic engineering of plants for the production of renewable hydrocarbon fuels.

Stearoyl-acyl carrier protein desaturases are associated with floral isolation in sexually deceptive orchids

“…However, because housekeeping desaturase activity should be ubiquitous and not restricted to alkene-producing tissues, other proteins must be involved to ensure that desaturation products enter the VLCFA elongation pathway in flowers. For example, changes in the activities of acyl-ACP thioesterase or acyl-CoA synthetase isoforms (12,13) would be potential candidates. Several orchid genera related to Ophrys produce low levels of alkenes, which might have served as a preadaptation for sexual deception in Ophrys (17).…”

“…Alkanes are synthesized from fatty acyl-coenzyme A (CoA) intermediates that undergo several rounds of chain elongation from the carboxyl terminus. These fatty acid (FA) intermediates undergo reduction to aldehydes and decarbonylation to form alkanes, mostly producing odd-numbered alkanes from even-numbered very-longchain fatty acid (VLCFA) intermediates (12,13). Alkenes are thought to follow the same synthesis scheme, except for the introduction of double-bonds in an additional desaturation step (6).…”

Functional expression and characterization of five wax ester synthases in Saccharomyces cerevisiae and their utility for biodiesel production

“…For example, wax esters consisting of fatty acids with 20 carbon atoms (C 20 ) and C 20 alcohols are outstanding lubricants [2]; wax esters consisting of C 14 to C 20 fatty acids and a C 2 alcohol represent good diesel fuels [3]. Today, wax esters are harvested from plants and animal tissues, or generated by chemical synthesis using fossil sources, and this is considered to be the main limitation for their application due to the restricted availability and high costs of existing sources [2,4]. Thus, there is a strong demand for the development of an alternative bioprocess to obtain cheap and sustainable wax esters.…”

“…Designed wax ester mixtures that do not normally exist in nature can be generated by expressing mutant WSs or a combination of WSs. It has become feasible to produce biotechnological wax esters in bioreactors [2,4,5,7-10]. The types of wax esters synthesized by a specific WS are determined by the WS substrate preference and available substrates provided through the host's metabolism.…”

“…There are three unrelated families of WSs found in higher plants, mammals and bacteria [2]. The first identified WS of plants, jojoba embryo wax ester synthase, did not show activity when heterologously expressed in S. cerevisiae [10].…”