Why study unusual plant fatty acids?

Plant membrane lipids contain primarily 6-9 different fatty acid structures that are 16 or 18 carbons long and have 0 to 3 double bonds.  These structures are the same in the membranes of vegetative tissues of almost all higher plants.

In striking contrast, fatty acids found in plant seeds are extremely diverse. More than 300 different FA structures have been reported to occur in plant seeds.  Some examples of classes of unusual plant fatty acids:

Why is it interesting and useful to study these fatty acids? (Adapted from a presentation by Ed Cahoon)

Biotechnology -- Help farmers and save the planet:  Many unusual fatty acids have high value for applications in industry but are not produced in sufficient quantity. Engineering the ‘normal’ fatty acid composition of oilseed crops has been extremely successful.    Achieving the same success with high-value unusual fatty acids is an important goal for society that would provide new income for farmers and new renewable resources to replace petroleum.

Bioprospecting -- Discover interesting new molecules:   Much of the chemodiversity of plant fatty acids was discovered as a result of screening carried out from 1960-1990. A major goal of these projects was the search for new industrial oils.   But many branches of plant evolution have not yet been surveyed and many structures remain to be discovered.

Understand enzyme structure-function relationships: Many unusual fatty acids in plant seeds are produced by enzymes that evolved as variants of enzymes of membrane fatty acid metabolism.   Comparing the structure of these proteins can reveal insights into enzyme reaction mechanisms and provides a window into “catalytic plasticity”.

Discover novel pathways and novel biochemistry:   Although we know much about the enzymes that synthesize many unusual fatty acids, there are still pathways that remain a mystery. RNASeq is now a fast and inexpensive method to reveal candidate enzymes involved in specialized seed metabolism.

Uncover how evolution shaped seed biochemistry:   The occurrence of unusual fatty acid structures in different branches of plant phylogeny can tell us about parallel and convergent evolution of enzymes and reveal new insights into how pathways evolved.

Are there more unique fatty acid structures still to be discovered?

Examination of all the plant species represented in PlantFAdb-SOFA, together with recent phylogenetic information allows us to identify branches in plant evolution whose seeds may not have been analyzed for fatty acid composition. Perhaps 25% of plant orders and 50% of plant families have not been analyzed for FA composition. Therefore, many (perhaps more than 100) new fatty acid structures might yet be discovered.  This table presents information on branches of the plant kingdom that have had little or no fatty acid analysis.

  It is important to note that many novel fatty acids may have been missed in previous analyses because they do not elute from standard GC columns, or were missed due to their instability to derivatization or other procedures. HPLC and newer lipidomic techniques will allow more types of structures to be discovered.  A very valuable review of methods for analysis of unusual FA in seeds is:   Spitzer, V. (1999)  Screening analysis of unknown seed oils   Lipid/Fett , 101 (1), 2-19.  doi:10.1002/(SICI)1521-4133(19991)101:1<2::AID-LIPI2>3.0.CO;2-H

Selected reviews:   

Badami, R.C., and Patil, K.B.    (1981). Structure and Occurrence of Unusual Fatty Acids in Minor Seed Oils. Progress in Lipid Research 19,119-153.    10.1016/0163-7827(80)90002-8

Christensen, L.P., and Brandt, K.    (2006). Acetylenes and Psoralens , in Plant Secondary Metabolites: Occurrence, Structure and Role in the Human Diet 137-173.    10.1002/9780470988558.ch5  

Dembitsky, V.M., and Srebnik, M.    (2002). Natural Halogenated Fatty Acids: Their Analogues and Derivatives. Progress in Lipid Research 41, 315-367.     10.1016/s0163-7827(02)00003-6

Hildebrand, D.    (2010) Production of Unusual Fatty Acids in Plants        http://lipidlibrary.aocs.org/Biochemistry/content.cfm?ItemNumber=40317

Mangold, H.K. and Spener, F.,    (1977). The cyclopentenyl fatty acids. In Lipids and Lipid Polymers in Higher Plants (pp. 85-101). Springer Berlin Heidelberg.  ISBN: 978-3-642-66632-2 (Online)

Mawlong, I., Sujith Kumar, M.S., and Singh, D. (   2014). Furan Fatty Acids: Their Role in Plant Systems.  Phytochemistry  Reviews 15, 121-127.     10.1007/s11101-014-9388-7

McKeon, T., Hayes, D., Hildebrand, D., & Weselake, R. (Eds.).       (2016).Industrial Oil Crops. Elsevier. eBook ISBN :9780128053850

Napier, J.A.    (2007). The Production of Unusual Fatty Acids in Transgenic Plants. Annu Rev Plant Biol 58, 295-319.   10.1146/annurev.arplant.58.032806.103811

Shanklin, J., and Cahoon, E. B. (1998). Desaturation and related modifications of fatty acids. Annual Review of Plant Biology, 49, 611-641.

Spitzer, V. (1999)  Screening analysis of unknown seed oils   Lipid/Fett , 101 (1), 2-19.  doi:10.1002/(SICI)1521-4133(19991)101:1<2::AID-LIPI2>3.0.CO;2-H