Nucleotide variation in ATHK1 region of Arabidopsis thaliana and its association study with drought tolerance

The ATHK1 gene in Arabidopsis encodes a putative histidine kinase that is transcriptionally up-regulated in response to changes in external osmolarity. In this work, we investigated the nucleotide variability of the ATHK1 gene in a sample of 32 core Arabidopsis accessions originating from different ecoclimatic regions and their drought tolerance. The results showed that different accessions had quite difference in adaptation to drought stress. Thirty-two Arabidopsis accessions were clustered into four groups according to their drought tolerance capacity. Relative water content of the leaves ( RWC) combined anyone of membrane permeability of leaves ( MP) and water retain capacity of detached leaves ( WRC) were selected as two representative physiological indexes for evaluation of comprehensive drought tolerance. Sequencing 5 515 bp encompassing ATHK1 coding region in 32 core accessions revealed 39 polymorphisms, which formed 24 haplotypes. The polymorphism ( including single nucleotide polymorphism ( SNP) and insertion/ deletion ( Indel)) frequency was 1 SNP per 131.2 bp. In coding region of ATHK1, the ratio of average number of nucleotide difference n/s ratio was 0.727, suggesting that the ATHK1 protein is not constrained against amino acid changes within the species and this gene belonged to the middle evolution rate gene. Using ANOVA analysis, it showed that the 1199 site amino acid ( Ser <-> stop) variation of the eleventh haplotype ( 257 and 266av) was associated with not only RWC but also WRC, indicating that the change of Ser <-> stop is associated with comprehensive drought tolerance of 257 and 266av. This amino acid change may cause 257 and 266 av accessions originating from moist ecoclimatic region to be sensitive to dry climate, and likely be the evidence of adaptive evolution.