QTL Mapping and Candidate Gene Identification of Swollen Root Formation in Turnip.

Yudi Wu,Guoliang Li,Chuchuan Fan,Rifei Sun,Hui Zhang,Shujiang Zhang,Shifan Zhang,Fei Li

doi:10.3390/ijms22020653

Abstract

The swollen root is an important agronomic trait and is a determinant of yield for turnips, which are cultivated as both vegetables and fodder. However, the genetic mechanism of swollen root formation is poorly understood. In this study, we analyzed the F2 and BC1P2 populations derived from a cross between “10601” (European turnip with swollen root, Brassica rapa ssp. rapifera, AA, 2n = 2× = 20) and “10603” (Chinese cabbage with normal root, Brassica rapa ssp. pekinensis, AA, 2n = 2× = 20), and suggested that the swollen root is a quantitative trait. Two major quantitative trait loci (QTLs), FR1.1 (Fleshy root 1.1) and FR7.1 (Fleshy root 7.1), were identified by QTL-seq analysis and further confirmed by QTL mapping in F2 and BC1P2 populations. The QTL FR1.1 with a likelihood of odd (LOD) of 7.01 explained 17.2% of the total phenotypic variations for root diameter and the QTL FR7.1 explained 23.0% (LOD = 9.38) and 31.0% (LOD = 13.27) of the total phenotypic variations in root diameter and root weight, respectively. After a recombinant screening, the major QTL FR7.1 was further narrowed down to a 220 kb region containing 47 putative genes. A candidate gene, Bra003652, which is a homolog of AT1G78240 that plays an essential role in cell adhesion and disorganized tumor-like formation in Arabidopsis thaliana, was identified in this region. In addition, expression and parental allele analysis supported that Bra003652 was a possible candidate gene of QTL FR7.1 for swollen root formation in turnip. Our research may provide new insight into the molecular mechanism of swollen root formation in root crops.

Highlights

IntroductionRapifera, AA, 2n = 2× = 20), which is cultivated for use as a vegetable, medicine, and fodder, is characterized by a swollen root
Turnip (Brassica rapa ssp. rapifera, AA, 2n = 2× = 20), which is cultivated for use as a vegetable, medicine, and fodder, is characterized by a swollen root
The bottom part of hypocotyls from the two parents was selected for the anatomical sections, and we found that the phloem (Ph), vascular cambium (VC), xylem (X), vessel

Summary

Introduction

Rapifera, AA, 2n = 2× = 20), which is cultivated for use as a vegetable, medicine, and fodder, is characterized by a swollen root. The turnip represents an important type in B. rapa, which displays considerable morphological diversity (leafy vegetables, oil crop, and stem/root crop). The swollen root is an important storage organ, which contains sugar, proteins, minerals, and many kinds of vitamins, and determines the yield and quality of turnip. Understanding the molecular mechanism underlying swollen root formation is important for improving root crops performance. Anatomical observation has identified that morphological changes of the xylem lead to an initiation of swollen root formation [6]. The genetic mechanism underlying swollen root formation and its regulation remains unknown

Results

Discussion

Conclusion