Genes Determining Anthocyanin Pigmentation in Different Parts of Wheat Plant
In bread wheat, anthocyanin pigments determine purple (culm, leaf blades, leaf sheaths, glumes, anthers, and grain pericarp), red/purple (coleoptile and auricles) or blue (aleurone layer) coloration (Fig. 16.1). Most genes determining anthocyanin pigmentation of different parts of wheat plant have been already identified and mapped (Khlestkina 2013b; McIntosh et al. 2013).
Mapping of the Genes Determining Anthocyanin Pigmentation Traits
Three genes for red coleoptile (Rc) localized on chromosomes 7A (Sears 1954), 7B (Gale and Flavell 1971), and 7D (Jha 1964) have been precisely mapped in homoeologous positions of the chromosome arms 7AS, 7BS, and 7DS and designated RcA1, Rc-B1, and Rc-D1, respectively (Khlestkina et al. 2002). Three homoeologous genes for purple culm (Pc-A1, Pc-B1, Pc-D1), three homoeologues for purple leaf sheaths (Pls-A1, Pls-B1, Pls-D1) and three homoeologues for purple leaf blades (Plb-A1, Plb-B1, Plb-D1) have been mapped in close linkage with red coleoptile genes Rc-A1, Rc-B1, and Rc-D1 (Khlestkina et al. 2009a, 2010b). Two genes determining purple anther (Pan-A1 and Pan-D1) have been mapped on chromosomes 7A (Blanco et al. 1998) and 7D (Khlestkina et al. 2009a) at a short distance from Rc-A1 and Rc-D1, respectively.
Two complementary genes for purple pericarp, Pp1 and Pp3, have been mapped in chromosomes 7B and 2A of bread (Arbuzova et al. 1998; Dobrovolskaya et al. 2006) and durum (Khlestkina et al. 2010a) wheat. For the durum gene Pp1 (Pp-B1), the homoeologue has been identified on chromosome 7D (Pp-D1) of bread wheat (Tereshchenko et al. 2012b). They have been mapped on the short arms of chromosomes 7B and 7D close to the Rc-B1 and Rc-D1, respectively. The Pp3 gene of durum wheat is closely linked to the gene for purple glume (Pg), however, unlike purple pericarp, the purple glume color is a monogenically inherited trait (Khlestkina et al. 2010a).
Chromosome locations and a number of the genes for red auricles (Ra) still remain a matter of contention. The genes determining this trait have been assigned
Fig. 16.1 Anthocyanin pigmentation of different parts of wheat plant. The picture was taken from (Khlestkina 2012) with modifications
to chromosomes 7A and 7D (Jha 1971), 1D (Gulyaeva 1984), 4B or 6B (Melz and Thiele 1990). None of these loci has been mapped. The reason for inconsistency in determining chromosome location and inability of mapping of the Ra genes is unstable expression of this trait. Near-isogenic lines and modern DNA-based genotyping approaches provide a powerful means of chromosome localization and fine mapping of genes with unstable expression. Using this approach we localized recently the gene Ra-D1 in a vicinity of Rc-D1 on chromosome 7DS (Khlestkina et al. 2014). There is a good agreement between our data and that reported by Jha (1971).
The blue aleurone (Ba) color had been inherited by wheat from its related species (Zeven 1991). For instance, the Ba genes have been identified in Thynopirum ponticum (Ba1; Keppenne and Baenziger 1990), Th. bessarabicum (BaThb; Shen et al. 2013), T. monococcum (Ba2; Dubcovsky et al. 1996), T. boeoticum (Ba2; Singh et al. 2007). In blue-grained wheat lines, alien substitutions or introgressions into homoeologous group 4 chromosomes are usually observed (Zeven 1991; Arbuzova et al. 2012; Shen et al. 2013).
Comparative mapping data in wheat, rice, and maize indicate that loci for anthocyanin pigmentation, mapped to homoeologous group 7 chromosomes, are orthologous to the maize gene C1 and rice gene OsC1, encoding Myb-like transcription activators of anthocyanin biosynthesis (Saitoh et al. 2004; Khlestkina 2013b). Furthermore, the maize C1 gene was used as a probe in Southern hybridizationbased mapping in wheat, and its homologue has been mapped to chromosome 7D (Li et al. 1999) in position highly comparable with that of the wheat Rc/Pc/Pls/Plb/ Pan/Pp1 genic cluster.
Similarly, comparative mapping data demonstrate that the wheat Pp3 gene is orthologous to rice Pb /Ra (Hu et al. 1996; Wang and Shu 2007) and maize Lc /R (Ludwig et al. 1989), encoding Myc-like protein needed for anthocyanin biosynthesis regulation. Recently nucleotide sequence of the candidate gene for Pp3 was isolated from wheat genome (Shoeva et al. 2014b).
Thus, the inter-genera comparative mapping suggests the anthocyanin biosynthesis genes on homoeologous group 7 chromosomes to encode Myb-like (C1-like) regulatory factors and that on chromosome 2A to encode Myc-like regulatory factors. Following this suggestion, the effect of different alleles of the Rc, Pc, Pls, Plb, and Pp genes on transcriptional activity of the ABP structural genes was investigated using wheat precise genetic stocks (see below).