Castor bean (Ricinus communis L.) is an important oilseed crop for industrial use. Castor oil contains approximately 90% ricinoleic acid (RA) which is stored mainly in the form of tri‐ricinoleic acid containing triacylglycerols (TAG). 

Phospholipase D (PLD) is a major family of enzymes that hydrolyzes membrane phospholipids in plants. It can convert PtdCho to phosphatidic acid (PtdOH), which is then converted to DAG by PAP. However, the functions of PLD in RA accumulation are yet to be identified. 

Researchers from Xishuangbanna Tropical Botanical Garden (XTBG) examined the Castor Bean Genome Database to identify all PLD homologous genes in castor.  

Expression pattern analysis showed that RcPLD9, which is a homolog of Arabidopsis PLDζ2, uniquely has high expression in developing seeds but not in other tissues. 

The expression of RcPLD9 in the Arabidopsis CL7 line, which expresses RcFAH12 in a fatty acid elongase 1 background, resulted in a lower RA content in the polar lipid fraction and mono‐HFA‐TAG fraction, but a higher RA content in the di‐HFA‐TAG fraction in seed oil. 

The decrease in HFA, 18:1n‐9 and 18:3n‐3, and the increase of 18:2n‐6 in polar lipids also indicated a probable relationship between the level of HFA and the activity of FAD2 or FAD3. 

Since the production of di‐HFA‐TAG likely requires the involvement of HFA‐DAG, the results of the study indicate that RcPLD9 contributed to the chanelling of HFA from PtdCho to DAG, and the assembly of di‐HFA‐TAG in developing seeds. 

The study entitled “Characterization of a PLDζ2 Homology Gene from Developing Castor Bean Endosperm” has been published in Lipids. 

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TIAN Bo  Ph.D 

Key Laboratory of Tropical Plant Resources and Sustainable Use, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun 666303, Yunnan, China