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Title:   Author  item
                                            BAEK, DONGWON - Texas Tech Universityitem
                                            JIANG, JIAFU - Texas Tech Universityitem
                                            CHUNG, JUNG SUNG - Texas Tech Universityitem
                                            Chen, Junpingitem
                                            Xin, Zhanguoitem
                                            SHI, HAUZHONG - Texas Tech University
  Submitted to: Plant Cell Physiology
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 11/16/2010
                                    Publication  Date: 1/1/2011
                                    Citation: Baek, D., Jiang, J., Chung, J., Chen, J., Xin, Z., Shi, H. 2011. Regulated AtHKT1 gene expression by a distal enhancer element and DNA methylation in the promoter plays an important role in salt tolerance. Plant Cell Physiology. 52(1):149-161.Interpretive Summary: 
Salt stress is worldwide problem. Through mutant screen from Arabidopsis, a new salt tolerance determinant AtHKT1 (At4g10310), the Arabidopsis thaliana High-affinityK+ Transporter1, was identified. It has been shown to be a crucial to salt tolerance, but its molecular mechanisms for Na+ uptake and transport in whole plant level still remains elusive. We identified a heavily methylated region in the enhancer of this gene about 2.6 Kb upstream of the ATG start codon. CHG and CHH methylation but not CG methylation is remarkably reduced in the small RNA biogenesis mutant rdr2, indicating that non-CG methylation in this region is mediated by small RNAs. Analysis of AtHKT1 expression in rdr2 suggests that non-CG methylation in the putative small RNA targeted region represses AtHKT1 expression in leaf. DNA methylation deficient mutant met1-3 has nearly complete loss of total cytosine methylation in the putative small RNA targeted region and is hypersensitivity to salt stress. The putative small RNA targeted region and the tandem repeat are essential for maintaining AtHKT1 expression pattern crucial for salt tolerance. This work identified a novel regulation of salt tolerance by small RNA.
                                Technical Abstract: The Arabidopsis thaliana High-affinityK+ Transporter 1 (AtHKT1, At4g10310) is a crucial salt tolerance determinant, but its molecular mechanisms for Na+ uptake and transport in whole plant level still remains elusive. Through sos3 (salt overly sensitive 3) suppressors screening, two allelic suppressor mutants that are weak alleles of the strong sos3 suppressor sos3hkt1-1 were recovered. Molecular characterization identified T-DNA insertions in the distal promoter region of AtHKT1 gene in these two weak sos3 suppressors, which results in physical separation of a tandem repeat from the proximal region of AtHKT1 promoter. The tandem repeat is approximately 3.9 Kb upstream of the ATG start codon and functions as an enhancer element to promote reporter gene expression. A putative small RNA targeted region about 2.6 Kb upstream of the ATG start codon is heavily methylated. CHG and CHH methylation but not CG methylation is remarkably reduced in the small RNA biogenesis mutant rdr2, indicating that non-CG methylation in this region is mediated by small RNAs. Analysis of AtHKT1 expression in rdr2 suggests that non-CG methylation in the putative small RNA targeted region represses AtHKT1 expression in leaf. DNA methylation deficient mutant met1-3 has nearly complete loss of total cytosine methylation in the putative small RNA targeted region and is hypersensitivity to salt stress. The putative small RNA targeted region and the tandem repeat are essential for maintaining AtHKT1 expression pattern crucial for salt tolerance.


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