ИСТИНА

Introduction The extent and pattern of DNA sequence variation in natural populations can help to uncover the evolutionary forces acting on a species. One of the ways in which those forces can act on a species are climatic conditions, e.g., temperature. Traits exhibiting patterns of clinal variation represent excellent models for studies of molecular adaptation, especially when variation in phenotype can be linked to fitness in different environments [1]. Our previous work has shown that nuclear-encoded chloroplast RNA-polymerase RpoTp mutation negatively affects the accumulation of cold response gene transcripts in response to low temperature. Results When considering all the ecotypes, the nucleotide diversity of RpoTp and RpoTmp (π = 0.0020 and 0,0015, respectedly) was the same or relatively lower compared to several A. thaliana genes studied previously [0.0031 - 0.0104 reviewed in 3 and 4], but much lower than the overall level of genome-wide polymorphism in A. thaliana estimated by values between 0.06 and 0.07 [5, 6]. Negative Tajima’s D values were observed in both genes indicating the presence of an excess of low-frequency polymorphism. Consistent with these tests, we could not detect a trace of positive or balancing selection. However, when scanned different regions of the RpoTp and RpoTmp genes using sliding windows of the Tajima's D test we identify regions which deviated from neutral expectations. Grouping ecotypes according to their geographic origin we were able to compare the nucleotide diversity between groups of the ecotypes from the southern, temperate, and northern ranges. It was demonstrated that the populations from the northern, temperate, and southern regions had almost the same nucleotide polymorphism of the both gene sequences Conclusions Our results indicate that both studied genes are under strong negative selection.