As one of the three main cereal crops worldwide, common wheat (Triticum aestivum L., 2n = 6x = 42, AABBDD), provides more than 20% of the calories consumed by the human population (Gao 2021). With the rapid growth of human population, wheat global production still needs to be enhanced to meet the increasing demand in the coming decades (https://www.fao.org/faostat/en/#data/QCL). Improving wheat yield per unit is an important way to solve this problem. Grain yield is a complex agronomic trait controlled by multiple genes, and is affected by three major components: thousand-grain weight (TGW), grain number per spike (GNS), and spike number per unit area (Wang et al. 2018; Zhang et al. 2022). Wheat spike morphology is mainly characterized by spikelet number (SPN), spike length (SPL) and spike compactness (SC), which is closely related to TGW and GNS. Therefore, genetic improvement of wheat spike traits is an effective way to achieve high grain yield (Panda et al. 2020).
The multiple sessile spikelets of wheat interlacing along the central spike axis can directly develop into compound spike, and the development is a complex biological process influenced by multiple genetic and physiological factors (Gao et al. 2019). Wheat spike differentiation development could be divided into three consecutive steps: spike meristem initiation and development, spikelet meristem development and floret meristem development. A few genes related to these stages have been identified. Vernalization (VRN), Photoperiod (Ppd), Flowering locus (FT), and domestication gene Q all regulate the spike meristem initiation and development stage (Yan et al. 2004, 2006; Fu et al. 2005; Beales et al. 2007; Li et al. 2008; Zhang et al. 2011; Kippes et al. 2014; Boden et al. 2015; Greenwood et al. 2017; Dixon et al. 2018; Zhang et al. 2019). At the spikelet meristem development stage, WHEAT FRIZZY PANICLE (WFZP) in AP2 gene family, SQUAMOSA promoter binding protein-like 14 (TaSPL14), AGAMOUS-LIKE6-like (TaAGL6), and WHEAT ABERRANT PANICLE ORGANIZATION 1 (WAPO1) are mainly functioned (Dobrovolskaya et al. 2014; Cao et al. 2021; Kong et al. 2022; Kuzay et al. 2022). At the last stage, crucial genes, such as Grain Number Increase1 (GNI1), SQUAMOSA and SHORT VEGETATIVE PHASE (SVP), regulate the meristem development of floret (Sakuma et al. 2013). The interaction between SQUAMOSA and SVP can promote the terminal spikelet formation and stem elongation in early reproductive stage of wheat (Li et al. 2021a). Recently, TaCOL-B5 encoding a CONSTANS-like protein, a gene increased spikelet nodes number per spike and produced more tillers and spikes was cloned in emmer wheat (Zhang et al. 2022).
Wheat spike morphology traits, SPL, SPN and SC, are all controlled by polygenes. Many studies have paid attention to identify the quantitative trait loci (QTL) conditioned these traits. To date, a large number of QTLs for SPL, SPN and SC, distributing on most wheat chromosomes, have been identified by linkage mapping or genome-wide association study (Ma et al. 2007; Gao et al. 2015; Guo et al. 2018; Li et al. 2018; Li et al. 2021b; Ma et al. 2018; Ma et al. 2019; Si et al. 2023). Specifically, QTLs with major effects or detected in multiple populations on SPL have been found on chromosomes 1A, 2D, 3A, 3D, 4A, 4B, 5A, 6A, 6B, 7A, 7B and 7D; and those associated with SPN on 1B, 2A, 2D, 3D, 5B, 7A and 7D (Ma et al. 2019; Ding et al. 2022; Si et al. 2023) and those associated with SC on 2D, 5A and 6A (Hu et al. 2023; Li et al. 2021b). However, few QTLs have been validated and fine-mapped.
It is an effective approach to identify the QTLs/genes of the target trait based on the mutant induced by EMS (Abe et al. 2012; Takagi et al. 2015; Deng et al. 2019; Zhou et al. 2020). In this study, we characterized a compact spike shape mutant ZM1160 from an EMS mutagenized population of common wheat variety Zhoumai32. The objectives were to (1) identify and clone the candidate gene related to the spike shape, and (2) develop the candidate gene-specific markers efficiently tracking the superior haplotype in common wheat.