Identification and expression analysis of castor bean (Ricinus communis) genes encoding enzymes from the triacylglycerol biosynthesis pathway

Castor bean (Ricinus communis) oil contains ricinoleic acid-rich triacylglycerols (TAGs). As a result of its physical and chemical properties, castor oil and its derivatives are used for numerous bio-based products. In this study, we survey the Castor Bean Genome Database to report the identification of TAG biosynthesis genes. A set of 26 genes encoding six distinct classes of enzymes involved in TAGs biosynthesis were identified. In silico characterization and sequence analysis allowed the identification of plastidic isoforms of glycerol-3-phosphate acyltransferase and lysophosphatidate acyltransferase enzyme families, involved in the prokaryotic lipid biosynthesis pathway, that form a cluster apart from the cytoplasmic isoforms, involved in the eukaryotic pathway. In addition, two distinct membrane bound diacylglycerol acyltransferase enzymes were identified. Quantitative expression pattern analyses demonstrated variations in gene expressions during castor seed development. A tendency of maximum expression level at the middle of seed development was observed. Our results represent snapshots of global transcriptional activities of genes encompassing six enzyme families involved in castor bean TAG biosynthesis that are present during seed development. These genes represent potential targets for biotechnological approaches to produce nutritionally and industrially desirable oils.

Research highlights▶ Seed oil from the castor bean contains high quantities of ricinoleic acid-rich triacylglycerides. Due to its physical and chemical properties, castor oil and its derivatives present numerous uses as bio-based products. Efforts to transfer genes encoding the proteins responsible for unusual fatty acid biosynthesis to higher yielding plants have generally produced limited success. Heterologous expression of castor bean genes in Arabidopsis thaliana, for example, increased hydroxyl-fatty acid content of only 17% in seed oils. This level is much lower than that found in castor oil (90%). Therefore, additional genes must be identified and significantly, more knowledge of seed oil biosynthesis is needed before plants can be engineered to produce industrially modified oils. In the present manuscript, we have made a systematic analysis of the Castor Bean Genome Database (http://castorbean.jcvi.org) and report the identification of 26 genes representing six classes of enzymes that participate in different steps of TAG biosynthesis. Furthermore, we have characterized the expression profiles of these genes during seed maturation. The present results will contribute to the understanding of the overlapping and specialized functions of genes from TAG metabolic pathways, and improve the choice of useful targets for biotechnological approaches.