MYB1 transcription factor is a candidate responsible for red root skin in radish (Raphanus sativus L.).

Gibum Yi,Suhyung Park,Hosub Shin,June-Sik Kim,Seung Hwa Yu,Jeong Eun Park,Jin Hoe Huh,Yong Pyo Lim

doi:10.1371/journal.pone.0204241

Abstract

Root skin color is one of the economically important traits in radish (Raphanus sativus), and the pigmentation in red skin varieties is largely attributable to anthocyanin accumulation. Pelargonidin was found as a major anthocyanin pigment accumulated in the sub-epidermal layer of red radish roots. In the 20 F2 population generated from the F1 with red root skins, root skins with red and white colors segregated in a 3:1 ratio. Additionally, a test cross between a red F3 individual and a white skin individual gave rise to 1:1 segregation of red and white, indicating that the root skin color of radish is determined by a single locus and red color is dominant over white. We performed association mapping for root skin color using SNPs obtained from RNA-seq analysis. Segregation analysis on the 152 F3 test-cross population revealed an RsMyb1 transcription factor as a candidate gene to determine root skin color. A PCR marker based on the polymorphism within 2 kb of RsMyb1 was developed and tested on 12 and 152 individuals from F2 and F3 test cross populations, respectively, and red and white root skin colors were completely distinguished corresponding to the genotypes. Expression levels of RsMyb1 in red or purple root cultivars were significantly higher than in white root cultivars. These findings suggest that RsMyb1 is a crucial determinant for anthocyanin biosynthesis in radish roots, and the molecular marker developed in this study will be useful for marker-assisted selection for red skin individuals at early seedling stages.

Highlights

R7 to root skin color, we have carefully chosen candidate genes according to the following criteria: first, differential expression levels between red and white root radishes (S3 Fig); second, root-specific expression reported in the Radish Genome Database; and third, regulatory functions for anthocyanin biosynthesis reported in other plant species
Root skin color is an interesting phenotype in radish, varying from white, yellow, red, and purple to black among others
In 1923, Frost reported that a cross between red and white root radishes produced the F1 plants with purple or violet-pink roots, suggesting that purple color was dominant over red and white colors and that white radish cultivars carried a purple gene since all the F1 plants were purple or violet [5]

Summary

Introduction

A single major peak associated with root skin color was identified on radish chromosome R7 (Fig 3b), and it is highly plausible that this region (9.11–11.78 Mb) contains the R locus responsible for root color determination. R7 to root skin color, we have carefully chosen candidate genes according to the following criteria: first, differential expression levels between red and white root radishes (S3 Fig); second, root-specific expression reported in the Radish Genome Database (radish-genome.org); and third, regulatory functions for anthocyanin biosynthesis reported in other plant species.

Results

Conclusion