Citrus sinensis MYB Transcription Factor CsMYB85 Induce Fruit Juice Sac Lignification Through Interaction With Other CsMYB Transcription Factors.

Ning Jia,Fengjiao Xin,Minmin Li,Jiameng Liu,Yatao Huang,Yufeng Sun,Jing Sun,Penghui Tan,Jiqin Liu,Khandaker Md Sharif Uddin Imam,Nuo Jin,Bei Fan,Yuemeng Lv,Jia Lu

doi:10.3389/fpls.2019.00213

Abstract

Varieties of Citrus are commercially important fruits that are cultivated worldwide and are valued for being highly nutritious and having an appealing flavor. Lignification of citrus fruit juice sacs is a serious physiological disorder that occurs during postharvest storage, for which the underlying transcriptional regulatory mechanisms remain unclear. In this study, we identified and isolated a candidate MYB transcription factor, CsMYB85, that is involved in the regulation of lignin biosynthesis in Citrus sinensis, which has homologs in Arabidopsis and other plants. We found that during juice sac lignification, CsMYB85 expression levels increase significantly, and therefore, suspected that this gene may control lignin biosynthesis during the lignification process. Our results indicated that CsMYB85 binds the CsMYB330 promoter, regulates its expression, and interacts with CsMYB308 in transgenic yeast and tobacco. A transient expression assay indicated that Cs4CL1 expression levels and lignin content significantly increased in fruit juice sacs overexpressing CsMYB85. At4CL1 expression levels and lignin content were also significantly increased in Arabidopsis overexpressing CsMYB85. We accordingly present convincing evidence for the participation of the CsMYB85 transcription factor in fruit juice sac lignification, and thereby provide new insights into the transcriptional regulation of this process in citrus fruits.

Highlights

Varieties of Citrus are commercially important fruits cultivated worldwide that are valued for being highly nutritious and having an appealing flavor
CsMYB85 isolated from sweet orange (C. sinensis) and its orthologs in other plants play important roles in lignin biosynthesis
In a phylogenetic tree constructed for MYB transcription factors, we found that CsMYB85 was clustered with the lignin-related AtMYB85 and AtMYB42 (Figure 1B), which may regulate lignin biosynthesis (Zhong et al, 2008)

Summary

Introduction

Varieties of Citrus are commercially important fruits cultivated worldwide that are valued for being highly nutritious and having an appealing flavor. Citrus fruit juice sac granulation (lignification) is a serious physiological disorder that occurs during the postharvest storage of these fruits (Shomer et al, 1989). The pulp tissue becomes hard and lignified, CsMYB85 Induce Juice Sac Lignification which diminishes fruit nutritional and commercial value (Pan et al, 1999). As fruit juice sac granulation increases, the cell walls thicken by lignification. Previous studies have demonstrated that juice sac lignin content increases during granulation and plays a vital role in this process (Zhang et al, 2016; Jia et al, 2018). An in-depth functional study of lignin biosynthesis-related genes may enhance our understanding of juice sac granulation

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