Identification of glume coloration genes in synthetic hexaploid and common wheats

Elena K. Khlestkina¹, Marion S. Roder², Andreas Borner²

¹Institute of Cytology and Genetics, Siberian Branch, Russian Academy of Sciences, Lavrentjeva ave. 10, Novosibirsk, 630090, Russia

²Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstr. 3, D-06466 Gatersleben, Germany

Corresponding author: Elena K. Khlestkina

E-mail: khlest@bionet.nsc.ru

Abstract

Crosses of hexaploid wheats having phenotype for glume color distinct from that reported in previous studies, were preformed and used to clarify whether these phenotypes are determined by new or earlier identified Rg alleles. It was found that although a common wheat accession ‘TRI 14341’ has not typical black glabrous glume, its glume color is controlled by the known allele Rg-A1c (chromosome 1AS). Dark brown-black glume color of the synthetic wheat line analysed in the current study was controlled by the two alleles Rg-A1c (1AS) and Rg-D1b (1DS). Rg-D1b was mapped 3.9 cM proximal to the microsatellite marker Xgwm1223, which is more precise mapping result than that obtained in the previous studies.

Introduction

Three homoeologous loci controlling glume coloration in hexaploid common wheat (Triticum aestivum L.) or synthetic hexaploid wheat were mapped to the short arms of chromosomes 1AS (Rg-A1), 1BS (Rg-B1) and 1DS (Rg-D1) (Khlestkina et al. 2006, 2009). Multiple allelism was shown for Rg-A1 and Rg-D1, since besides recessive colorless (wildtype) allele two different dominant alleles were found at each of these loci. Alleles Rg-A1b and Rg-A1c controlling red and black glume coloration, respectively, whereas Rg-D1b and Rg-D1c control red and smokey-grey color. Rg-A1b was described only in several Russian T. aestivum cultivars (Efremova et al. 1998). Rg-A1c was described in T. aestivum near-isogenic line ‘i:S29BgHg’, in which black glume color is known to be closely linked to glume hairiness (Arbuzova et al. 1998). Rg-D1b inherited from the D-genome progenitor of hexaploid wheat (Aegilops tauschii) was described in synthetic hexaploid wheats only (Kerber and Dyck 1969, Jones et al. 1990, Borner et al. 2002). Rg-D1c was described in single T. aestivum Russian cultivar ‘Golubka’ (Pshenichnikova et al. 2005).

In the current study, crosses of hexaploid wheats having phenotypes distinct from that of the previously studied accessions (namely, synthetic wheat having dark brown-black glume and T. aestivum accession having rare black glabrous glume phenotype) were preformed and used to clarify whether these phenotypes are determined by new or by earlier identified Rg alleles.

Materials and methods

Two crosses between hexaploid wheat lines and accessions were used to create F₂ populations: (1) synthetic hexaploid line (McFadden and Sears 1947) having dark brown-black glume was crossed with white-glumed Russian cultivar ‘Ulyanovka’. 146 F₂ plants were obtained, genotyped and scored for glume coloration, and (2) accession ‘TRI 14341’ (IPK-Genebank collection) having black glabrous glume was crossed with white-glumed ‘TRI 542’, which is known to carry dominant Hg allele for hairy glume (Khlestkina et al. 2006). Fifty-one F₂ plants were obtained and scored for glume coloration and hairiness.

DNA from frozen leaves of ‘Synthetic’/‘Ulyanovka’ F2progeny was extracted according to Plaschke et al. (1995). Six chromosome 1A and nine chromosome 1D GWM (Gatersleben Wheat Microsatellites) markers were found to be polymorphic within the ‘Synthetic’/‘Ulyanovka’ population and used for mapping. Experimental details regarding microsatellite assays are described in Roder et al. 1998. Linkage maps were constructed with MAPMAKER 2.0 (Lander et al. 1987). Centimorgan distances were calculated applying the Kosambi map-unit function (Kosambi 1944).

Results and Discussion

Segregation ratio for glume coloration in F₂ population ‘Synthetic’/‘Ulyanovka’ was 134 colored: 12 non-colored plants, corresponding to digenic 15:1 (χ²=0.966, P>0.30). Therefore, we suggested that the synthetic wheat may carry black glume color allele Rg-A1c inherited from the tetraploid emmer wheat and red glume color allele Rg-D1b inherited from Ae. tauschii. Chromosome 1A and 1D polymorphic microsatellites (6 and 9 markers, respectively) were used for genotyping of the F₂ lines. Linkage maps obtained are presented at Fig. 1. Dobrovolskaya et al. (2006) have mapped one of the two complementary Pp (purple pericarp) genes in population with digenic segregation, using microsatellite genotyping data for selection of genotypes recessive for the other gene. Similarly, suggesting that the synthetic parent of the ‘Synthetic’ / ‘Ulyanovka’ F₂ population may carry allele Rg-A1c which was previously mapped 0.6 cM proximal to Xgwm1223 on chromosome 1AS, we selected genotypes having ‘Ulyanovka’ microsatellite alleles at the locus Xgwm1223 and also at the locus Xgwm1104 flanking suggested Rg-A1c location site from the other side. Therefore 27 F₂ genotypes were selected, from which 22 had colored and 5 non-colored glumes, corresponding to 3:1 (χ²=0.606, P>0.30). This genotyping data were used for mapping glume color gene one chromosome 1D. The gene was mapped 3.9 cM proximal from 1DS locus Xgwm1223 (Fig. 1). Earlier allele Rg-D1b originating from synthetic ‘W7984’ was mapped 11.6 cM proximal to the microsatellite locus Xgwm1223 (Khlestkina et al. 2009) using ITMI mapping population, whereas T. aestivum ‘Golubka’ allele Rg-D1c, controlling smokey-grey glume color, was mapped 1.5 cM proximal to Xgwm1223 (Khlestkina et al. 2006). We suggest the gene mapped in the current study on chromosome 1DS is Rg-D1b (Fig. 1), however using ‘Synthetic’ / ‘Ulyanovka’ cross it was mapped more precisely than in ITMI mapping population. After establishment of Rg-D1b precise map position, we used the flanking markers Xgwm1223 and Xgwm0106 genotyping data to select F₂ plants carrying ‘Ulyanovka’ alleles, in order to map the synthetic glume color gene on chromosome 1A. Thus, 19 genotypes were selected, from which 13 had colored and 6 non-colored glumes, corresponding to 3:1 (χ²=0.439, P>0.50). This genotyping data were used for mapping glume color gene one chromosome 1A. The gene was mapped 0.7 cM proximal from 1AS locus Xgwm1223 (Fig. 1), in a position highly comparable with that determined for allele Rg-A1c controlling black glume color in T. aestivum near-isogenic line ‘i:S29BgHg’ (0.6 cM proximal to Xgwm1223; Khlestkina et al. 2006). In the near-isogenic line ‘i:S29BgHg’ Rg-A1c was also shown to be closely linked to dominant allele at the locus Hg (hairy glume; Khlestkina et al. 2006). These two traits (black glume and hairy glume) were known to be usually closely linked and often occur in tetraploid wheat, whereas in common wheat most of the accessions and cultivars have white or red glumes, and the former may sometimes have hairy glumes (Philipchenko 1935, Zeven 1983). Therefore, it was interesting to identify which gene determine glume color in T. aestivum accession ‘TRI 14341’ having black glabrous glume. We crossed it with white-glumed accession ‘TRI 542’ known to carry dominant allele of the gene Hg on 1AS. There were no plants with white glabrous glumes within F2 progeny of this cross, suggesting black glume gene of ‘TRI 14341’ to be closely linked with recessive allele of locus Hg. Therefore, we concluded that allele determining black glume color in ‘TRI 14341’ is identical to Rg-A1c of ‘i:S29BgHg’.

Thus, it was found that glume color in T. aestivum accession ‘TRI 14341’ having black glabrous glume is controlled by allele Rg-A1c (chromosome 1AS), whereas dark brown-black glume color of the synthetic wheat line analyzed in the current study is controlled by the two alleles Rg-A1c (1AS) and Rg-D1b (1DS). Rg-D1b was mapped more precisely (Fig. 1) than in the previous study (Khlestkina et al. 2009). It also can be concluded that, using microsatellite markers, it is possible to map major genes even if digenic segregation in the mapping population is observed.

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