Small RNAs Prevent Transcription-Coupled Loss of Histone H3 Lysine 9 Methylation in Arabidopsis thaliana

In eukaryotes, histone H3 lysine 9 methylation (H3K9me) mediates silencing of invasive sequences to prevent deleterious consequences including the expression of aberrant gene products and mobilization of transposons. In Arabidopsis thaliana, H3K9me maintained by SUVH histone methyltransferases (MTases) is associated with cytosine methylation (5meC) maintained by the CMT3 cytosine MTase. The SUVHs contain a 5meC binding domain and CMT3 contains an H3K9me binding domain, suggesting that the SUVH/CMT3 pathway involves an amplification loop between H3K9me and 5meC. However, at loci subject to read-through transcription, the stability of the H3K9me/5meC loop requires a mechanism to counteract transcription-coupled loss of H3K9me. Here we use the duplicated PAI genes, which stably maintain SUVH-dependent H3K9me and CMT3-dependent 5meC despite read-through transcription, to show that when PAI sRNAs are depleted by dicer ribonuclease mutations, PAI H3K9me and 5meC levels are reduced and remaining PAI 5meC is destabilized upon inbreeding. The dicer mutations confer weaker reductions in PAI 5meC levels but similar or stronger reductions in PAI H3K9me levels compared to a cmt3 mutation. This comparison indicates a connection between sRNAs and maintenance of H3K9me independent of CMT3 function. The dicer mutations reduce PAI H3K9me and 5meC levels through a distinct mechanism from the known role of dicer-dependent sRNAs in guiding the DRM2 cytosine MTase because the PAI genes maintain H3K9me and 5meC at levels similar to wild type in a drm2 mutant. Our results support a new role for sRNAs in plants to prevent transcription-coupled loss of H3K9me

Testing a Short Nuclear Marker for Inferring Staphylinid Beetle Diversity in an African Tropical Rain Forest

The use of DNA based methods for assessing biodiversity has become increasingly common during the last years. Especially in speciose biomes as tropical rain forests and/or in hyperdiverse or understudied taxa they may efficiently complement morphological approaches. The most successful molecular approach in this field is DNA barcoding based on cytochrome c oxidase I (COI) marker, but other markers are used as well. Whereas most studies aim at identifying or describing species, there are only few attempts to use DNA markers for inventorying all animal species found in environmental samples to describe variations of biodiversity patterns.In this study, an analysis of the nuclear D3 region of the 28S rRNA gene to delimit species-like units is compared to results based on distinction of morphospecies. Data derived from both approaches are used to assess diversity and composition of staphylinid beetle communities of a Guineo-Congolian rain forest in Kenya. Beetles were collected with a standardized sampling design across six transects in primary and secondary forests using pitfall traps. Sequences could be obtained of 99% of all individuals. In total, 76 molecular operational taxonomic units (MOTUs) were found in contrast to 70 discernible morphospecies. Despite this difference both approaches revealed highly similar biodiversity patterns, with species richness being equal in primary and secondary forests, but with divergent species communities in different habitats. The D3-MOTU approach proved to be an efficient tool for biodiversity analyses.Our data illustrate that the use of MOTUs as a proxy for species can provide an alternative to morphospecies identification for the analysis of changes in community structure of hyperdiverse insect taxa. The efficient amplification of the D3-marker and the ability of the D3-MOTUs to reveal similar biodiversity patterns as analyses of morphospecies recommend its use in future molecular studies on biodiversity

閉會인사

韓日國際硏究會議「東아시아의 死生學으로」, 2010.11.20, 코리아나 호텔, 서