ABA mediates development-dependent anthocyanin biosynthesis and fruit coloration in Lycium plants

Gen Li,Zixin Mu,Yue Yin,Youlong Cao,Jianhua Zhao,Wei An,Beibei Qin

doi:10.1186/s12870-019-1931-7

Abstract

BackgroundAnthocyanins, which are colored pigments, have long been used as food and pharmaceutical ingredients due to their potential health benefits, but the intermediate signals through which environmental or developmental cues regulate anthocyanin biosynthesis remains poorly understood. Fleshy fruits have become a good system for studying the regulation of anthocyanin biosynthesis, and exploring the mechanism underlying pigment metabolism is valuable for controlling fruit ripening.ResultsThe present study revealed that ABA accumulated during Lycium fruit ripening, and this accumulation was positively correlated with the anthocyanin contents and the LbNCED1 transcript levels. The application of exogenous ABA and of the ABA biosynthesis inhibitor fluridon increased and decreased the content of anthocyanins in Lycium fruit, respectively. This is the first report to show that ABA promotes the accumulation of anthocyanins in Lycium fruits. The variations in the anthocyanin content were consistent with the variations in the expression of the genes encoding the MYB-bHLH-WD40 transcription factor complex or anthocyanin biosynthesis-related enzymes. Virus-induced LbNCED1 gene silencing significantly slowed fruit coloration and decreased both anthocyanin and ABA accumulation during Lycium fruit ripening. An qRT-PCR analysis showed that LbNCED1 gene silencing clearly reduced the transcript levels of both structural and regulatory genes in the flavonoid biosynthetic pathway.ConclusionsBased on the results, a model of ABA-mediated development-dependent anthocyanin biosynthesis and fruit coloration during Lycium fruit maturation was proposed. In this model, the developmental cues transcriptionally activates LbNCED1 and thus enhances accumulation of the phytohormone ABA, and the accumulated ABA stimulates transcription of the MYB-bHLH-WD40 transcription factor complex to upregulate the expression of structural genes in the flavonoid biosynthetic pathway and thereby promoting anthocyanin production and fruit coloration. Our results provide a valuable strategy that could be used in practice to regulate the ripening and quality of fresh fruit in medicinal and edible plants by modifying the phytohormone ABA.

Highlights

Anthocyanins, which are colored pigments, have long been used as food and pharmaceutical ingredients due to their potential health benefits, but the intermediate signals through which environmental or developmental cues regulate anthocyanin biosynthesis remains poorly understood
Because the relationship between the LbNCED1 transcript amount and the Abscisic acid (ABA) level has been determined in Lycium chinense, one of the redcolored Lycium fruits [31], the present study further detected this relationship in Lycium fruits with two other important colors, YF and BF
The results showed that the content of the endogenous hormone ABA and the LbNCED1 gene expression level increased with fruit ripening in both colors of the fruits

Summary

Introduction

Anthocyanins, which are colored pigments, have long been used as food and pharmaceutical ingredients due to their potential health benefits, but the intermediate signals through which environmental or developmental cues regulate anthocyanin biosynthesis remains poorly understood. ABA plays an important role in plant growth, stomatal movement, seed dormancy and germination, and the plant response to biotic and abiotic stress [14] These ABA-mediated physiological processes are mainly affected by the regulation of the size of the bioactive ABA pool [15, 16]. Numerous studies have shown that ABA is generally involved in the regulation of fruit ripening in both climacteric and nonclimacteric fruits [2, 6, 16], in which the NCED gene plays an important role [8, 15, 17,18,19,20,21,22,23]. Whether NCED-derived ABA is involved in anthocyanin-mediated fruit ripening in medicinal and edible plants remains poorly understood [24]

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