Castor patatin-like phospholipase A IIIß facilitates removal of hydroxy fatty acids from phosphatidylcholine in transgenic Arabidopsis seeds

Authors: LIN, YINGYU - UNIVERSITY OF ALBERTA; CHEN, GUANQUN - UNIVERSITY OF ALBERTA; MIETKIEWSKA, ELZBIETA - UNIVERSITY OF ALBERTA; SONG, ZILIANG - UNIVERSITY OF ABERTAY; CALDO, KRISTIAN MARK - UNIVERSITY OF ALBERTA; SINGER, STACY - UNIVERSITY OF ALBERTA; Dyer, John; SMITH, MARK - AGRICULTURE AND AGRI-FOOD CANADA; MCKEON, THOMAS; WESELAKE, RANDALL - UNIVERSITY OF ALBERTA

Submitted to: Plant Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/4/2019
Publication Date: 9/23/2019
Citation: Lin, Y., Chen, G., Mietkiewska, E., Song, Z., Caldo, K.P., Singer, S.D., Dyer, J.M., Smith, M., McKeon, T.A., Weselake, R.J. 2019. Castor patatin-like phospholipase A IIIß facilitates removal of hydroxy fatty acids from phosphatidylcholine in transgenic Arabidopsis seeds. Plant Molecular Biology. 101:521-536. https://doi.org/10.1007/s11103-019-00915-w.
DOI: https://doi.org/10.1007/s11103-019-00915-w

Interpretive Summary: Many non-domesticated plant species produce high amounts of “unusual” fatty acids in their seed oil, many of which have desirable properties for use in high-value industrial applications. Several examples include the hydroxy fatty acids present in the seed oils of castor bean or Physaria fendleri, which have potential usage in formulations of varnishes, cosmetics, surfactants, and engine oil lubricants. Castor bean and P. fendleri, however, have undesirable agronomic traits that limit their usage in the large-scale production of these valuable feedstocks for industry. Metabolic engineering offers an attractive approach for resolving this problem by transferring genes for hydroxy fatty acid synthesis to other crops that have better agronomic traits. Experiments to date have indicated, however, that relatively low amounts of hydroxy fatty acids are produced in engineered crops due to inefficiencies in transfer of these fatty acids into the oil of developing seeds. In the current study, scientists from the University of Alberta, Agriculture and Agri-Food Canada, and the ARS labs in Maricopa, Arizona, and Albany, California, identified a gene in castor bean that helps relieve this bottleneck, which shows promise for future studies aimed at further increasing hydroxy fatty acid content in engineered crops. These findings will be of greatest interest to other scientists interested in understanding the genes and enzymes required for production of high value oils in crop plants, as well as companies involved in the production and distribution of these oils for industrial partners and other end users.

Technical Abstract: Hydroxy fatty acids (HFAs) are industrial useful, but their major natural source castor contains toxic components. Although expressing a castor OLEATE 12-HYDROXYLASE in Arabidopsis thaliana leads to the synthesis of HFAs in seeds, a high proportion of the HFAs are retained in phosphatidylcholine (PC). Thus, the liberation of HFA from PC seems to be critical for obtaining HFA-enriched seed oils. Plant phospholipase A (PLA) catalyzes the hydrolysis of PC to release fatty acyl chains that can be subsequently channeled into triacylglycerol (TAG) synthesis or other metabolic pathways. To further our knowledge regarding the function of PLAs from HFA-producing plant species, two class III patatin-like PLA cDNAs (pPLAIIIß or pPLAIIId) from castor or Physaria fendleri were overexpressed in a transgenic line of A. thaliana producing C18-HFA, respectively. Only the overexpression of RcpPLAIIIß resulted in a significant reduction in seed HFA content with concomitant changes in fatty acid composition. Reductions in HFA content occurred in both PC and TAG indicating that HFAs released from PC were not incorporated into TAG. These results suggest that RcpPLAIIIß may catalyze the removal of HFAs from PC in the developing seeds synthesizing these unusual fatty acids.