Tissue-specific differences in metabolites and transcripts contribute to the heterogeneity of ricinoleic acid accumulation in Ricinus communis L. (castor) seeds
Castor (Ricinus communis L.) seeds are valued for their production of oils which can comprise up to 90% hydroxy-fatty acids (ricinoleic acid). Castor oil contains mono-, di- and tri- ricinoleic acid containing triacylglycerols (TAGs). Although the enzymatic synthesis of ricinoleic acid is well described, the differential compartmentalization of these TAG molecular species has remained undefined.
To examine the distribution of hydroxy fatty acid accumulation within the endosperm and embryo tissues of castor seeds.
Matrix assisted laser desorption/ionization mass spectrometry imaging was used to map the distribution of triacylglycerols in tissue sections of castor seeds. In addition, the endosperm and embryo (cotyledons and embryonic axis) tissues were dissected and extracted for quantitative lipidomics analysis and Illumina-based RNA deep sequencing.
This study revealed an unexpected heterogeneous tissue distribution of mono-, di- and tri- hydroxy-triacylglycerols in the embryo and endosperm tissues of castor seeds. Pathway analysis based on transcript abundance suggested that distinct embryo- and endosperm-specific mechanisms may exist for the shuttling of ricinoleic acid away from phosphatidylcholine (PC) and into hydroxy TAG production. The embryo-biased mechanism appears to favor removal of ricinoleic acid from PC through phophatidylcholine: diacylglycerol acyltransferase while the endosperm pathway appears to remove ricinoleic acid from the PC pool by preferences of phospholipase A (PLA2α) and/or phosphatidylcholine: diacylglycerol cholinephosphotransferase.
Collectively, a combination of lipidomics and transcriptomics analyses revealed previously undefined spatial aspects of hydroxy fatty acid metabolism in castor seeds. These studies underscore a need for tissue-specific studies as a means to better understand the regulation of triacylglycerol accumulation in oilseeds.
KeywordsMALDI RNA-Seq Castor Ricinoleic acid Lipidomics Hydroxy fatty acids
This work was supported in part by the U.S Department of Energy, Office of Science, BES-Physical Biosciences program (DE-SC0016536 to KDC; DE-SC0012704 to JS), by the National Science Foundation (Grant DBI 1117680, X-H Y, JS), and by a UNT-dissertation summer stipend to Drew Sturtevant. The UNT Orbitrap XL mass spectrometer and cryostat facilities were supported in part by a grant from the Hoblitzelle Foundation. The transcriptomics data were collected and reads processed for analysis by the UNT- BioDiscovery Genomics Core Facility.
The MALDI-MSI imaging and transcriptome sequencing and analysis were completed by DS. TR completed the MALDI-MS and ESI-MS analysis of lipid extracts. Bioinformatics support was contributed by DB, supervised by RA. XY grew and collected plant material and performed the real-time, quantitative-PCR (RT-qPCR) analyses on developing seeds. KC and JS supervised experiments at UNT and Brookhaven National Laboratory, respectively. DS, TR, and KC drafted the manuscript. All authors contributed to editing of the manuscript.
This research was funded in part by research contracts from the United States Department of Energy, Office of Science, Basic Energy Sciences (DE-SC0016536 to KDC; DE-SC0012704 to JS), a grant award from the National Science Foundation (DBI 1117680, X-H Y, JS), and by a UNT-dissertation summer stipend to Drew Sturtevant.
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Conflict of interest
All authors declare that they have no conflicts of interest.
Research involving human and animal participants
This article does not contain any studies with human participants or animals performed by any of the authors.
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