Abstract
The wax (glaucousness) on wheat leaves and stems is mainly controlled by two sets of genes: glaucousness loci (W1 and W2) and non-glaucousness loci (Iw1 and Iw2). The non-glaucousness (Iw) loci act as inhibitors of the glaucousness loci (W). High-resolution comparative genetic linkage maps of the wax inhibitors Iw1 originating from Triticum dicoccoides, and Iw2 from Aegilops tauschii were developed by comparative genomics analyses of Brachypodium, sorghum and rice genomic sequences corresponding to the syntenic regions of the Iw loci in wheat. Eleven Iw1 and eight Iw2 linked EST markers were developed and mapped to linkage maps on the distal regions of chromosomes 2BS and 2DS, respectively. The Iw1 locus mapped within a 0.96 cM interval flanked by the BE498358 and CA499581 EST markers that are collinear with 122 kb, 202 kb, and 466 kb genomic regions in the Brachypodium 5S chromosome, the sorghum 6S chromosome and the rice 4S chromosome, respectively. The Iw2 locus was located in a 4.1 to 5.4-cM interval in chromosome 2DS that is flanked by the CJ886319 and CJ519831 EST markers, and this region is collinear with a 2.3 cM region spanning the Iw1 locus on chromosome 2BS. Both Iw1 and Iw2 co-segregated with the BF474014 and CJ876545 EST markers, indicating they are most likely orthologs on 2BS and 2DS. These high-resolution maps can serve as a framework for chromosome landing, physical mapping and map-based cloning of the wax inhibitors in wheat.
Highlights
The outermost wax layer protects plants from many types of biotic and abiotic stresses, such as drought, phytophagous insects, pathogens, solar radiation, and freezing temperatures [1,2]
The 1161 recombinant inbred lines (RIL) of the International Triticea Mapping Initiative (ITMI) population segregated as 549 non-glaucousness and 612 glaucousness to fit the expected 1:1 ratio (Table 1)
These results indicate that non-glaucousness in the WE74, TA4152–60, and W7984 wheat lines is controlled by single dominant wax inhibitor gene
Summary
The outermost wax layer protects plants from many types of biotic and abiotic stresses, such as drought, phytophagous insects, pathogens, solar radiation, and freezing temperatures [1,2]. One of the most important roles of the cuticle is to limit transpiration to reduce water loss and this provides a key mechanism for plant survival in water-limited environments, such as deserts, high mountains, saline-alkali lands, and coastal ecosystems [3,4]. Physiological studies in wheat by Johnson et al [7] and Richards et al [8] showed that glaucousness reduces transpiration and increased water use efficiency. More recently Zhang et al demonstrated that glaucousness reduced cuticle permeability in the terms of nonstomatal water loss and chlorophyll efflux [9]. Bread wheat cultivars with non-glaucousness traits exhibit significant yield increases with reduced solar radiation losses that enable continued photosynthesis during the grain filling period [10], and the trait may provide resistance to aphids [11]
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