Location: Plant Physiology and Genetics ResearchTitle: Molecular characterization of the fatty alcohol oxidation pathway for wax-ester mobilization in germinated jojoba seeds Author
Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/16/2012
Publication Date: 11/19/2012
Citation: Rajangam, A.S., Gidda, S.K., Craddock, C., Mullen, R.T., Dyer, J.M., Eastmond, P.J. 2012. Molecular characterization of the fatty alcohol oxidation pathway for wax-ester mobilization in germinated jojoba seeds. Plant Physiology. 161:72-80. Interpretive Summary: Jojoba is a shrub that is endemic to the arid southwest. It produces a "liquid wax" in its seeds rather than the typical type of oil produced in oilseed crops. Due its unique chemical structure and high lubricity, the liquid wax is an excellent component in formulations of skin creams and cosmetics, and if produced on larger scale, it could be used as petroleum alternative for hydraulic fluids, motor oil, transmission fluid, and perhaps even used in biofuels. One approach for producing higher amounts of jojoba-type liquid waxes is to use transgenic approaches to produce the wax in higher yielding platform crops such as oilseed rape or camelina, but to do so requires knowledge of the genes involved in both the synthesis of the liquid wax in seeds, as well as the enzymes required for breakdown of the oil to support post-germinative growth. In this manuscript, a consortium of scientists from the UK, Canada, and the ARS lab in Maricopa Arizona have identified and functionally characterized two of the key enzymes in jojoba that are involved in breaking down the wax esters to support post-germinative growth. The genes encoding these enzymes will be very useful in designing crop plants that are engineered to produce high amounts of liquid waxes in developing seeds, and will have greatest immediate impact on scientists and research programs that are focused on production of value-added, renewable chemicals in the seeds of plants.
Technical Abstract: Jojoba (Simmondsia chinensis) is the only plant species known to use liquid wax esters (WE) as a primary seed storage reserve. Upon germination, WE hydrolysis releases very long-chain fatty alcohols, which must be oxidised to fatty acids by the sequential action of a fatty alcohol oxidase (FAO) and a fatty aldehyde dehydrogenase (FADH), before they can be ß-oxidised. Here we describe the cloning and characterization of genes for each of these two activities. Jojoba FAO and FADH are 52% and 68% identical to Arabidopsis thaliana FAO3 and ALDH3H1, respectively. The genes are expressed most strongly in the cotyledons of jojoba seedlings following germination, but transcripts can also be detected in vegetative tissues. Proteomic analysis indicated that the FAO and FADH proteins can be detected on wax bodies, but they localised to the endoplasmic reticulum when they are expressed as N-terminal GFP fusions in tobacco leaves. Recombinant jojoba FAO and FADH proteins are active on very-long chain fatty alcohol and fatty aldehyde substrates, respectively and have biochemical properties consistent with those previously reported in jojoba cotyledons. Co-expression of jojoba FAO and FADH in Arabidopsis enhanced the in vivo rate of fatty alcohol oxidation more than 4-fold. Taken together, our data suggest that jojoba FAO and FADH constitute the very-long-chain fatty alcohol oxidation pathway that is likely to be necessary for efficient WE mobilisation following seed germination.