Isolation and characterization of AtMLH1, a MutL homologue from Arabidopsis thaliana

Abstract

DNA mismatch repair systems play an essential role in the maintenance of genetic information in living organisms and are also implicated in genetic recombination and genome stability. Using degenerate primers, we have cloned the first plant homologue of the E. coli MutL gene, which we have called AtMLH1 for Arabidopsis thaliana MutL-homologue 1. AtMLH1 is present as a single-copy gene in the Arabidopsis genome and is located on the top arm of chromosome 4. Sequence analysis revealed that the product of this gene shows extensive sequence homology with other eukaryotic MLH1 proteins. As mlh1-deficient lines would be useful for studying the biological function of this gene, several populations that had been mutagenized using T-DNA and transposon insertions were screened to identify such mutants. One line that carries a T-DNA insertion in the promoter region of the AtMLH1 gene was isolated. Surprisingly, although the insertion occurred only approximately 80 bp upstream of the putative transcription start site, Northern analyses revealed very low but similar amounts of AtMLH1 transcript in both the wild type and the T-DNA insertion lines. RT-PCR analyses suggest, however, that transcription is initiated further upstream in the insertion line and that the T-DNA may supply this novel initiation site. Finally, no increase in microsatellite instability - a phenotype often associated with mutations in mismatch repair genes - was observed in plants homozygous for this insertion.

The Arabidopsis DNA mismatch repair gene PMS1 restricts somatic recombination between homeologous sequences

“…Also, the increases in recombination frequency in Arabidopsis mutants are systematically lower than those observed in yeast mutants at the same or comparable level of divergence. This might be due to the low levels of MMR gene expression in plant somatic tissues (Adé et al 1999;Jean et al 1999), an explanation already invoked by Leonard et al (2003) to explain the relatively small increases (*5x) in microsatellite mutation rates seen in Arabidopsis mmr mutants compared to S. cerevisiae mutants where such increases are typically in the 100-to 10,000-fold range (Tran et al 1997). Such an explanation, however, may not hold as Lafleuriel et al (2007) monitored recombination in cells contributing to the Arabidopsis germ line.…”

Microarray expression analysis of meiosis and microsporogenesis in hexaploid bread wheat

“…Such transcripts would show co-regulation with known meiotic genes from within this meiotic data set. This assumption is supported by the close similarities in expression profiles between two related mismatch repair genes, TaMSH7 [39] and AtMLH1 [46] (correlation coefficient of 0.997).…”

Structure and expression of the Zea mays mutS-homologs Mus1 and Mus2

“…MutS and MutL homologs have been identified and partially characterized in A. thaliana (Culligan and Hays 1997;Adé et al 1999;Jean et al 1999;Adé et al 2001), and partial cDNAs of putative MMR genes were isolated from Triticum aestivum (Korzun et al 1999), rice, Brassica napus and soybean. Here we report on the identification, transcription and gene structure of two MutS homologous genes from maize, termed Mus1 and Mus2.…”