Transcriptional Analysis of Anthocyanin Biosynthesis Structural Genes in Different Wheat Organs
Using comparative transcriptional approach, regulatory role of the genes, determining anthocyanin pigmentation of wheat organs, has been investigated. Ahmed et al. (2006) compared expression of the ABP structural genes in the red and green coleoptiles of the chromosome substitution line 'Chinese Spring'('Hope' 7A) and cv.
Fig. 16.2 RT-PCR analysis of the anthocyanin biosynthesis structural genes in different organs of wheat 'Saratovskaya 29' (left in each pair) and its near-isogenic line 'i:S29Pp1Pp3P' (right in each pair). Anthocyanin extracts from the corresponding organs are shown below. Ubc (ubiquitin) – endogenous control
'Chinese Spring', respectively, and concluded that the Rc-A1 gene activates expression of the structural genes Dfr, Ans, and Ufgt. Later the regulatory role of the RcA1, Rc-B1, and Rc-D1 genes has been demonstrated using a wide range of wheat precise genetic stocks: near-isogenic and introgression lines, chromosome substitution and recombinant lines (Khlestkina et al. 2008, 2010b; Tereshchenko et al. 2013). In addition, it has been found that multiple dominant alleles of the same regulatory gene (Rc-A1) have different effects on dynamics and intensity of the structural gene expression (Khlestkina et al. 2010b).
Regulatory role of the Pc, Pls, Plb, and Pp genes has been demonstrated using near-isogenic lines (Fig. 16.2; Tereshchenko et al. 2013). It has been noted that the F3h gene is expressed only in colored tissues and is not expressed in non-colored ones such as roots of both lines or pericarp of 'Saratovskaya 29' (Fig. 16.2). The other structural genes are still transcribed in the absence of anthocyanin pigments, but at the lower level in comparison with the intensively colored tissues (Fig. 16.2; Tereshchenko et al. 2013). This specific regulation of F3h was also observed earlier by Khlestkina et al. (2009b) in coleoptiles of wheat-rye addition lines.
In some plant species, the whole set of anthocyanin biosynthesis genes is regulated as a single unit (Dooner 1983; Meldgaard 1992; Mato et al. 2000; Honda et al. 2002; Mano et al. 2007). In other plant species, anthocyanin biosynthesis can be regulated at different stages of the pathway (Boss et al. 1996; Ramazzotti et al. 2008; Zhao et al. 2012). However, the regulation of the anthocyanin biosynthesis at the stage of the F3h gene expression has been observed in wheat only and this may be a species-specific peculiarity of the anthocyanin biosynthesis regulation in Triticum. Such peculiarities of flavonoid biosynthesis regulation provide a basis for taxonomic distinguishing among plants (Bell 1980). However, biological meaning of the flavonoid biosynthesis interruption in non-colored tissues of wheat at the stage of F3H enzyme action, when flavanones are converted to dihydroflavonols, is not clear yet.
Anthocyanin pigments are reportedly the universal defense compounds produced in response to a wide range of biotic and abiotic stress factors. Most of the regulatory and structural anthocyanin biosynthesis genes have been mapped in wheat. The majority of the structural ABP genes and one of the two complementary genes determining purple grain trait have been sequenced. The other regulatory genes can be isolated and sequenced in the near future based on the data provided from investigations of their functions and from inter-genera comparative mapping. The knowledge of genetic basis of anthocyanins biosynthesis in wheat and the availability of wheat precise genetic stocks provide a highly appropriate basis for exploring the changes in expression of the ABP genes under stress conditions. These data will be useful in future for improvement wheat adaptation properties.
Acknowledgements This study was partially supported by RFBR (grant no 12-04-33027), grant from the President of the Russian Federation (МD-2615.2013.4) and the State Budget Programme (Project No VI.53.1.5.).