Phylogenetic relationships of genus Beta species based on the chloroplast trnK (matK) gene intron sequence information

Abstract

This was the first work to study the primary structure of the chloroplast lysine tRNA gene ( matK ) intron in beet species belonging to sections Beta and Procumbentes. It is demonstrated that this genome region is identical in all studied members of Beta section. Interspecies polymorphism was not found either in the species belonging to Procumbentes section. However, a comparison of sequences characterizing sections Beta and Procumbentes revealed distinctions between them in the studied fragment of the chloroplast genome. The history of beet studying began in 1753, when Carl Linnaeus described the cultivated beet under the name of Beta vulgaris L. By the end of XIX century, all wild beet forms have been already described. However, samples that were similar in certain morphological traits were named differently by different researchers [1]. In 1927, soviet botanist Transhel’ on the basis of analysis of herbarium samples and descriptions made by other researchers divided all species of the Beta genus into three sections: Patellares m., Vulgares m., and Corolliae m. [1]. Later, numerous attempts were made to supplement and improve this classification [2, 3]. This applied primarily to species of the Vulgares section, because sugar beet, which is of great agricultural importance as a source of sugar, belongs to this section. Study of morphological and biochemical markers made it possible to create a generally accepted system of classification of the Beta genus [4], according to which the Beta genus is divided into four sections: Beta (synonym Vulgares ), Corollinae, Nanae , and Procumbentes (synonym Patellares ). The Beta section includes three species, two of which are wild-growing ( B. macrocarpa Guss and B. patula Ait.). The third species of this section, B. vulgaris L., includes three subspecies, two of which are wild-growing (ssp. maritima (L.) Arcang and ssp. adanensis (Pamuk.) Ford-Lloyd and Will) and one cultivated (ssp. vulgaris ). The latter subspecies (cultivated beet) is divided into leaf, red, and sugar beet and mangel-wurzel. The development of molecular methods allowed data obtained by these techniques to be used for comparing different species of the Beta genus. For instance, a study of chloroplast and nuclear genes of the order Caryophyllales, to which the Beta genus belongs, showed that the matK gene is optimal for studying phylogenetic relationships within this order. Analysis based on the use of this gene made it possible to reveal more distinctions between Beta species than in the case of other chloroplast and nuclear genes [5]. In view of this, in studying the phylogeny of species of the Beta genus, we used a fragment of chloroplast lysine tRNA gene intron that contained the open reading frame (the matK gene) encoding the protein exhibiting maturase activity. The goal of this study was to determine the phylogenetic relationships between the members of the Beta genus (primarily the Beta section) on the basis of studying the nucleotide sequence of the intron fragment of the lysine tRNA gene ( trnK / matK ) of the chloroplast genome.