Identification and characterization of manganese tolerance genes in beta vulgaris subsp. Maritima

Abstract

Manganese is an essential element for higher organisms however uptake of excess amount of manganese causes toxicity. Beta vulgaris subsp. maritima, the member of Chenopodiaceae family, is known to tolerate high concentration of sodium. Due to its living conditions, Beta vulgaris subsp. maritima adapted many different stress conditions. Therefore it is an ideal plant for studying plant tolerance mechanisms. In this study, we aimed to identify the genes which are responsible for manganese tolerance in Beta vulgaris subsp. maritima by screening its cDNA library in Saccharomyces cerevisiae cells. After initial screening in the presence of toxic manganese concentration; 2,7mM MnCl2, three resistant yeast colonies were selected. After the sequence and similarity analysis, two genes which might involve in manganese tolerance were identified and named as BmMn1 and BmMn2. The results of solid media tests with different yeast strains which transformed with the genes revealed that BmMn1 provides a remarkable manganese tolerance like BmMn2 and slightly nickel tolerance. They do not show tolerance to other metals such as zinc, cadmium, boron and cobalt. Identified manganese concentrations in pmr1 yeast strainstransformed with BmMn1, BmMn2 or empty vector pointed that BmMn1 and BmMn2 transport excess manganese out of the cell. In addition, GFP localization in the yeast cell proved that the BmMn1 and BmMn2 are located in Golgi apparatus. qRT-PCR analyses of Beta vulgaris subsp. maritima which was exposed to 2mM Mn2+ suggested a dynamic regulation for the expression of these two genes. The results indicate that BmMn1 and BmMn2 have a role in detoxification of excess amount of manganese in Beta vulgaris subsp. maritima.