Genome-Wide Characterization of R2R3-MYB Transcription Factors in Pitaya Reveals a R2R3-MYB Repressor HuMYB1 Involved in Fruit Ripening through Regulation of Betalain Biosynthesis by Repressing Betalain Biosynthesis-Related Genes.

Fangfang Xie,Canbin Chen,Jietang Zhao,Guibing Hu,Rong Zhang,Yonghua Qin,Jianye Chen,Qingzhu Hua,Zhike Zhang

doi:10.3390/cells10081949

Fangfang Xie, Canbin Chen + Show 7 more

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https://doi.org/10.3390/cells10081949

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Abstract

The MYB (myeloblastosis) superfamily constitutes one of the most abundant transcription factors (TFs) regulating various biological processes in plants. However, the molecular characteristics and functions of MYB TFs in pitaya remain unclear. To date, no genome-wide characterization analysis of this gene family has been conducted in the Cactaceae species. In this study, 105 R2R3-MYB members were identified from the genome data of Hylocereus undatus and their conserved motifs, physiological and biochemical characteristics, chromosome locations, synteny relationship, gene structure and phylogeny were further analyzed. Expression analyses suggested that three up-regulated HuMYBs and twenty-two down-regulated HuMYBs were probably involved in fruit ripening of pitaya. Phylogenetic analyses of R2R3-MYB repressors showed that seven HuMYBs (HuMYB1, HuMYB21, HuMYB48, HuMYB49, HuMYB72, HuMYB78 and HuMYB101) were in clades containing R2R3-MYB repressors. HuMYB1 and HuMYB21 were significantly down-regulated with the betalain accumulation during fruit ripening of ‘Guanhuahong’ pitaya (H. monacanthus). However, only HuMYB1 had R2 and R3 repeats with C1, C2, C3 and C4 motifs. HuMYB1 was localized exclusively to the nucleus and exhibited transcriptional inhibition capacities. Dual luciferase reporter assay demonstrated that HuMYB1 inhibited the expression of betalain-related genes: HuADH1, HuCYP76AD1-1 and HuDODA1. These results suggested that HuMYB1 is a potential repressor of betalain biosynthesis during pitaya fruit ripening. Our results provide the first genome-wide analyses of the R2R3-MYB subfamily involved in pitaya betalain biosynthesis and will facilitate functional analysis of this gene family in the future.

Highlights

HuMYB1 acted as a nucleus-localized transcriptional repressor involved in betalain biosynthesis pathway by repressing the transcription of HuADH1, HuCYP76AD1-1 and HuDODA1 (Figure 8)
BvMYB1 is involved in betalain biosynthesis by targeting the CYP76AD1 and DODA promoter while HpWRKY44 has a functional role in the regulation of CYP76AD1 [17,43]
HuMYB transcription factors (TFs) are probably involved in betalain biosynthesis by binding to the HuADH1, HuCYP76AD1-1 and HuDODA1 promoters in pitaya

Summary

Introduction

Transcription factors (TFs) play important roles in plant growth and development by controlling gene expression, suppressing translation or activating transcription of target genes, or interacting with other proteins. Based on the MYB repeat number and the identity of the MYB repeats, MYB superfamily members are generally classified into four major subfamilies, namely, MYB-related (1R-MYB), R2R3-MYB (2R-MYB), R1R2R3-MYB (3R-MYB) and 4R-like MYB (4R-MYB) proteins. The smallest subfamily is the 4R-MYB group, whose members contain four R1/R2-like repeats in several plant genomes [3]. The 3R-MYB subfamily contains R1, R2 and R3 repeats and typically encoded by five genes in higher plant genomes. The 1R-MYB subfamily comprises proteins with a single or a partial MYB repeat and falls into several subclasses, including R3-type, R1/R2-type and the GARP family [4]

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