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Front. Plant Sci. | doi: 10.3389/fpls.2018.00212

Proanthocyanidin synthesis in Chinese bayberry (Myrica rubra Sieb. et Zucc.) fruits

Liyu Shi1, Shifeng Cao2, Xin Chen2, Wei Chen2, Yonghua Zheng1* and  Zhenfeng Yang2*
  • 1College of Food Science and Technology, Nanjing Agricultural University, China
  • 2College of Biological and Environmental Sciences, Zhejiang Wanli University, China

Proanthocyanidins (PAs) are distributed widely in Chinese bayberry fruit and have been associated with human health benefits, but molecular and biochemical characterization of PA biosynthesis remains unclear. Here, two genes encoding key PA biosynthetic enzymes, anthocyanidin reductase (ANR) and leucoanthocyanidin reductase (LAR) were isolated in bayberry fruit. MrANR was highly expressed at the early stage of fruit development when soluble PAs accumulated at high levels. Meanwhile, the transcript abundance of both MrANR and MrLAR observed at the late stage was paralleled with the high amounts of insoluble PAs. LC-MS/MS showed that PAs in developing Chinese bayberry fruits were comprised predominantly of epigallocatechin-3-O-gallate terminal subunits, while the extension subunits were a mixture of epigallocatechin-3-O-gallate, epigallocatechin and catechin. Recombinant MrANR protein converted cyanidin to a mixture of epicatechin and catechin, and delphinidin to a mixture of epigallocatechin and gallocatechin in vitro. Recombinant MrLAR was active with leucocyanidin as substrate to produce catechin. Ectopic expression of MrANR in tobacco reduced anthocyanin levels but increased PA accumulation. The catechin and epicatechin contents in transgenic flowers overexpressed MrANR were significantly higher than those of wild-type. However, overexpression of MrLAR in tobacco led to an increase in catechin levels but had no impact on PA contents. Quantitative real time PCR revealed that the loss of anthocyanin in transgenic flowers overexpressed MrANR or MrLAR is probably attributed to decreased expression of tobacco chalcone isomerase (CHI) gene. Our results not only reveal in vivo and in vitro functions for ANR and LAR but also provide a resource for understanding the mechanism of PA biosynthesis in Chinese bayberry fruit.

Keywords: Chinese bayberry, Proanthocyanidin, Flavan-3-ols, Anthocyanidin reductase, Leucoanthocyanidin reductase

Received: 04 Nov 2017; Accepted: 05 Feb 2018.

Edited by:

Kevin Davies, The New Zealand Institute for Plant & Food Research Ltd, New Zealand

Reviewed by:

Yongzhen Pang, Institute of Botany (CAS), China
Vinay Kumar, Central University of Punjab, India  

Copyright: © 2018 Shi, Cao, Chen, Chen, Zheng and Yang. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence:
Prof. Yonghua Zheng, Nanjing Agricultural University, College of Food Science and Technology, Nanjing, China, zhengyh@njau.edu.cn
Prof. Zhenfeng Yang, Zhejiang Wanli University, College of Biological and Environmental Sciences, Ningbo, China, yangzf@zwu.edu.cn