Theor Appl Genet
Comparative fine mapping of the Wax 1 (W1) locus in hexaploid wheat
Ping Lu1 · Jinxia Qin1 · Guoxin Wang1 · Lili Wang1 · Zhenzhong Wang1 ·
Qiuhong Wu1 · Jingzhong Xie1 · Yong Liang1 · Yong Wang1 · Deyun Zhang1 ·
Qixin Sun1 · Zhiyong Liu1
Received: 28 January 2015 / Accepted: 2 May 2015 © Springer-Verlag Berlin Heidelberg 2015
The wheat leaf, stem and, in some cases, spike surfaces are coated with cuticular waxes, which confers a glaucousness characteristic (Jensen and Driscoll 1962). Epicuticular waxes are composed of several classes of compounds, including very-long-chain fatty acids (VLCFA; >18C), esters, primary and secondary alcohols, fatty aldehydes and ketones (Kunst and Samuels 2003). As a barrier between plants and their environment, the outermost wax layer functions in defending plants against the biotic and abiotic stresses, such as drought, phytophagous insects, pathogens, solar radiation, and freezing temperatures (Eigenbrode and
Espelie 1995; Jenks and Ashworth 1999). Worldwide, bread wheat (Triticum aestivum L.) is one of the most important food sources for human beings. However, drought has long been a major threat to global crop production, and climate change exaggerates its scale and frequency. One of the most important functions of the cuticular wax is that it restricts non-stomatal water loss and protects plants against ultraviolet radiation and reduces water retention on the plant surface, thus minimizing deposition of dust, pollen and air pollutions (Kunst and Samuels 2003). Moreover, glaucousness significantly increased grain and biomass yield in irrigated and rain-fed field experiments in wheat (Johnson et al. 1983). Recently, Zhang et al. (2013) demonstrated that glaucousness reduced cuticle permeability in the terms of non-stomatal water loss and chlorophyll efflux.
Genetic analyses have revealed that the glaucousness and non-glaucousness phenotypes on wheat stem and leaf are mainly controlled by two sets of loci: the wax production genes W1 and W2 and the wax inhibitor genes Iw1 and
Iw2, respectively (Jensen and Driscoll 1962; Tsunewaki 1966; Tsunewaki and Ebana 1999). The wax production gene W1 and the wax inhibition gene Iw1 are closely linked
Key message By applying comparative genomics analyses, a high-density genetic linkage map of the Wax 1 (W1) locus was constructed as a framework for mapbased cloning.
Abstract Glaucousness is described as the scattering effect of visible light from wax deposited on the cuticle of plant aerial organs. In wheat, the wax on leaves and stems is mainly controlled by two sets of genes: glaucousness loci (W1 and W2) and non-glaucousness loci (Iw1 and Iw2).
Bulked segregant analysis (BSA) and simple sequence repeat (SSR) mapping showed that Wax1 (W1) is located on chromosome arm 2BS between markers Xgwm210 and Xbarc35. By applying comparative genomics analyses, colinearity genomic regions of the W1 locus on wheat 2BS were identified in Brachypodium distachyon chromosome 5, rice chromosome 4 and sorghum chromosome 6, respectively. Four STS markers were developed using the
Triticum aestivum cv. Chinese Spring 454 contig sequences and the International Wheat Genome Sequencing Consortium (IWGSC) survey sequences. W1 was mapped into a 0.93 cM genetic interval flanked by markers XWGGC3197 and XWGGC2484, which has synteny with genomic regions of 56.5 kb in Brachypodium, 390 kb in rice and 31.8 kb in sorghum. The fine genetic map can serve as a framework for chromosome landing, physical mapping and map-based cloning of the W1 in wheat.
Communicated by I. D. Godwin. * Zhiyong Liu email@example.com 1
State Key Laboratory for Agrobiotechnology/Department of Plant Genetics and Breeding, China Agricultural
University, Beijing 100193, China
Theor Appl Genet 1 3 on chromosome 2BS (Tsunewaki 1966). However, the wax inhibition gene Iw2 is located on the distal of 2DS where the wax production gene W2 is close to the centromere (Tsunewaki and Ebana 1999). Another two loci, Iw3 and
Ws, both derived from T. dicoccoides, were reported on 1BS (Dubcovsky et al. 1997) and 1AS (Gadaleta et al. 2009) conditioning wax on spikes in wheat. Recently, QTL for flag leaf glaucousness was also detected in wheat (Bennett et al. 2012).
High-resolution genetic linkage maps for wax inhibition genes Iw1 (Adamski et al. 2013; Wu et al. 2013), Iw2 (Wu et al. 2013) and Iw3 (Wang et al. 2014a) have been constructed. However, very little information is available for the wax production genes. (Tsunewaki 1966) demonstrated that the wax production gene W1 is located 2 cM away from the wax inhibition gene Iw1 on 2BS. Recent study suggested that the W1 gene was tightly linked with molecular markers Xbarc35 and Xwmc764 on chromosome 2BS (Yoshiya et al. 2011).
Fine mapping and map-based cloning in common wheat are difficult because of the large wheat genome size (17 Gb), polyploidy (AABBDD), and highly repetitive
DNA (90 %). The availability of wheat expressed sequence tags (EST) and the rice (Oryza sativa L.), sorghum (Sorghum bicolor L.), and Brachypodium distachyon genome sequences provide comparative genomics tools for wheat gene mapping and map-based cloning. The high-density genetic linkage maps of vernalization (VRN) genes (Yan et al. 2003, 2004, 2006), pairing homologous 1 (Ph1) (Griffiths et al. 2006), grain protein content-B1 (Gpc-B1) (Uauy et al. 2006), yellow rust resistance gene Yr36 (Fu et al. 2009) and powdery mildew resistance gene MlIW172 (Ouyang et al. 2014) were constructed through comparative genomics analysis. The recently released draft genome sequences of T. aestivum cv. Chinese Spring, T. urartu accession G1812 and Aegilops tauschii accession AL8/78 provide nearly complete gene sets of the wheat A, B and D genomes (Brenchley et al. 2012; Jia et al. 2013; Ling et al. 2013) for marker development and gene identification.
In this paper, we report the comparative genomic analysis and high-resolution genetic linkage map construction of the wax production gene Wax 1 (W1) as a framework for map-based cloning and marker-assisted selection in wheat breeding programs.