Molecular and biochemical analysis of the castor caruncle reveals a set of unique genes involved in oil accumulation in non-seed tissues

Xia Wan,Xue-Rong Zhou,Qing Liu,Surinder P Singh,Feng-Hong Huang,Sapna Vibhakaran Pillai,Bei Dong

doi:10.1186/s13068-019-1496-6

Abstract

BackgroundWith the increasing demand for vegetative oil and the approach of peak seed oil production, it is important to develop new oil production platforms from non-seed tissues. Castor bean (Ricinus communis) is one of the crops for vegetable oil for industrial applications with yield around 1.4 ton oil per hectare produced in seed. The castor caruncle is a non-seed tissue attached to seed.ResultsCaruncle accumulates up to 40% oil by weight in the form of triacylglycerol (TAG), with a highly contrasting fatty acid composition when compared to the seed oil. Biochemical analysis indicated that the caruncle synthesizes TAGs independent of the seed. Such non-seed tissue has provided an excellent resource for understanding the mechanism of oil accumulation in tissues other than seeds. Transcriptome analysis revealed the key members of gene families involved in fatty acid synthesis and TAG assembly in the caruncle. A transient expression assay of these selected genes resulted in a 20-fold increased TAG accumulation in leaves.ConclusionsCastor caruncle utilizes an independent system to synthesize TAGs. Results provide the possibility of exploiting caruncle gene set to engineer oil production in non-seed tissues or microbes.

Highlights

With the increasing demand for vegetative oil and the approach of peak seed oil production, it is important to develop new oil production platforms from non-seed tissues
Oil accumulation and sugar content in developing castor seeds and caruncles Castor seeds are rich in oil which is mainly stored in the endosperm
During seed development, which was divided into five stages based on morphologic characteristics [23] with the mature seed designated as stage 6, oil content of the seeds showed sharp increases at stages 4 and 5 (Fig. 1)

Summary

Introduction

With the increasing demand for vegetative oil and the approach of peak seed oil production, it is important to develop new oil production platforms from non-seed tissues. Vegetable oils are mainly extracted from seeds of soybean, rapeseed/canola, and sunflower, as well as from non-seed tissues, such as the mesocarp of oil palm, olive and avocado. The accumulation of high levels of oils in high biomass vegetative tissues such as leaves rather than seeds has been considered as a promising strategy to meet the increasing demands for vegetable oils [2,3,4]. Vegetable oils are mainly comprised of TAGs which typically account for only less than 1% of total leaf lipids [5]. The majority of DAG is converted into membrane lipids rather than TAGs [7].

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Conclusion