Dissection of Pleiotropic QTL Regions Controlling Wheat Spike Characteristics Under Different Nitrogen Treatments Using Traditional and Conditional QTL Mapping.

Xiaoli Fan,Junming Li,Jun Ji,Xueqiang Zhao,Tao Wang,Deyuan Meng,Yiping Tong,Jiajia Liu,Fa Cui,Wei Zhang

doi:10.3389/fpls.2019.00187

Abstract

Optimal spike characteristics are critical in improving the sink capacity and yield potential of wheat even in harsh environments. However, the genetic basis of their response to nitrogen deficiency is still unclear. In this study, quantitative trait loci (QTL) for six spike-related traits, including heading date (HD), spike length (SL), spikelet number (SN), spike compactness (SC), fertile spikelet number (FSN), and sterile spikelet number (SSN), were detected under two different nitrogen (N) supplies, based on a high-density genetic linkage map constructed by PCR markers, DArTs, and Affymetrix Wheat 660 K SNP chips. A total of 157 traditional QTLand 54 conditional loci were detected by inclusive composite interval mapping, among which three completely low N-stress induced QTL for SN and FSN (qSn-1A.1, qFsn-1B, and qFsn-7D) were found to maintain the desired spikelet fertility and kernel numbers even under N deficiency through pyramiding elite alleles. Twenty-eight stable QTL showing significant differencet in QTL detection model were found and seven genomic regions (R2D, R4A, R4B, R5A, R7A, R7B, and R7D) clustered by these stable QTL were highlighted. Among them, the effect of R4B on controlling spike characteristics might be contributed from Rht-B1. R7A harboring three major stable QTL (qSn-7A.2, qSc-7A, and qFsn-7A.3) might be one of the valuable candidate regions for further genetic improvement. In addition, the R7A was found to show syntenic with R7B, indicating the possibly exsting homoeologous candidate genes in both regions. The SNP markers involved with the above highlighted regions will eventually facilitate positional cloning or marker-assisted selection for the optimal spike characteristics under various N input conditions.

Highlights

Wheat (Triticum aestivum L.) is one of the leading cereal crops worldwide, and is critical for global food security
The results indicated that, regardless of N treatments, the Rht-B1b was associated with the significant reduction in plant height (PH) and sterile spikelet number (SSN), and a remarkable increase in kernel number per spike (KN), heading date (HD), spikelet number (SN), and fertile spikelet number (FSN), but no significant effect was detectedin the spike length (SL) and spike compactness (SC) (Table 4), which was coincident with the quantitative trait loci (QTL) mapping results (Table 3, Table S5)
This study provides further preliminary confirmation of the putative pleiotropic effect of Rht-B1 on spike characteristics (Table 4), which was consistent with the QTL mapping results (Table 3)

Summary

Introduction

Wheat (Triticum aestivum L.) is one of the leading cereal crops worldwide, and is critical for global food security. C, which is positioned in the interval of Xgwm484-Xgwm358-Xcfd17-Xgwm539 on chromosomes 2DL (Johnson et al, 2008), accounts for the very dense “club” spike of club wheat (Triticum compactum Host) and has a pleiotropic effect on spike compactness, grain size, shape, and number (Johnson et al, 2008) These three genes are no longer the main breeding target for genetic improvement in modern wheat (Zhai et al, 2016), because most common wheat cultivars have identical genotypes, i.e., QcS (Faris et al, 2014). The contributions of these wheat orthologous genes on spike characteristics need to be further specified, it could be preliminarily evaluated at the QTL level

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Results

Discussion

Conclusion