Identification of the Q Gene Playing a Role in Spike Morphology Variation in Wheat Mutants and Its Regulatory Network.

Jiazi Zhang,Shirong Zhao,Yuting Li,Jiayu Gu,Xiaomei Xie,Yuping Ding,Linshu Zhao,Yongdun Xie,Hongchun Xiong,Luxiang Liu,Huijun Guo

doi:10.3389/fpls.2021.807731

Abstract

The wheat AP2 family gene Q controls domestication traits, including spike morphology and threshability, which are critical for the widespread cultivation and yield improvement of wheat. Although many studies have investigated the molecular mechanisms of the Q gene, its direct target genes, especially those controlling spike morphology, are not clear, and its regulatory pathways are not well established. In this study, we conducted gene mapping of a wheat speltoid spike mutant and found that a new allele of the Q gene with protein truncation played a role in spike morphology variation in the mutant. Dynamic expression levels of the Q gene throughout the spike development process suggested that the transcript abundances of the mutant were decreased at the W6 and W7 scales compared to those of the WT. We identified several mutation sites on the Q gene and showed that mutations in different domains resulted in distinct phenotypes. In addition, we found that the Q gene produced three transcripts via alternative splicing and that they exhibited differential expression patterns in nodes, internodes, flag leaves, and spikes. Finally, we identified several target genes directly downstream of Q, including TaGRF1-2D and TaMGD-6B, and proposed a possible regulatory network. This study uncovered the target genes of Q, and the results can help to clarify the mechanism of wheat spike morphology and thereby improve wheat grain yield.

Highlights

The yield of grass crops is influenced by several factors, and because inflorescences produce seeds and determine yield, modifying the morphological structure of inflorescences can directly improve seed yield (Wang and Li, 2008)
We identified a wheat mutant, je0275, showing speltoid spike morphology resulting from ethyl methane sulfonate (EMS) mutagenesis (Figure 1A)
Two kinds of spike morphology segregated in the reciprocally crossed F2 populations, and the ratio of speltoid spikes to normal spikes was 3–1, as verified by the chi-square test (Supplementary Table 2). This ratio indicated that this spike morphology variation was controlled by a single gene and that the speltoid spike phenotype resulted from a dominant allele

Summary

Introduction

The yield of grass crops is influenced by several factors, and because inflorescences produce seeds and determine yield, modifying the morphological structure of inflorescences can directly improve seed yield (Wang and Li, 2008). The yield of wheat is a complex trait determined by the number of spikes per unit area, number of grains per spike and 1,000 grain weight, and spike morphology can influence grain yield by affecting the number of spikelets, florets, and fertility (Xie et al, 2018; Cao et al, 2020). Wheat domestication gene Q encodes an APETALA2-like transcription factor (TF) that controls domestication traits such as spike morphology, threshability, rachis fragility, plant height, and heading time, thereby affecting grain yield (Sears, 1954; Muramatsu, 1963; Kato et al, 1999, 2003; Faris and Gill, 2002; Faris et al, 2003, 2005; Xie et al, 2018; Debernardi et al, 2019; Liu et al, 2020). The Q gene has several AP2 family homologs, including the indeterminant spikelet (ids1) gene and sister of ids (sid1) in maize as well as the OsIDS gene in rice (Chuck et al, 1998, 2008; Lee and An, 2012)

Methods

Results

Conclusion