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Discovery of stress responsive DNA regulatory motifs in Arabidopsis.

ABSTRACT: The discovery of DNA regulatory motifs in the sequenced genomes using computational methods remains challenging. Here, we present MotifIndexer--a comprehensive strategy for de novo identification of DNA regulatory motifs at a genome level. Using word-counting methods, we indexed the existence of every 8-mer oligo composed of bases A, C, G, T, r, y, s, w, m, k, n or 12-mer oligo composed of A, C, G, T, n, in the promoters of all predicted genes of Arabidopsis thaliana genome and of selected stress-induced co-expressed genes. From this analysis, we identified number of over-represented motifs. Among these, major critical motifs were identified using a position filter. We used a model based on uniform distribution and the z-scores derived from this model to describe position bias. Interestingly, many motifs showed position bias towards the transcription start site. We extended this model to show biased distribution of motifs in the genomes of both A. thaliana and rice. We also used MotifIndexer to identify conserved motifs in co-expressed gene groups from two Arabidopsis species, A. thaliana and A. lyrata. This new comparative genomics method does not depend on alignments of homologous gene promoter sequences.

SUBMITTER: Ma S

PROVIDER: S-EPMC3418279 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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Discovery of stress responsive DNA regulatory motifs in Arabidopsis.

Ma Shisong S Bachan Shawn S Porto Matthew M Bohnert Hans J HJ Snyder Michael M Dinesh-Kumar Savithramma P SP

PloS one 20120813 8

The discovery of DNA regulatory motifs in the sequenced genomes using computational methods remains challenging. Here, we present MotifIndexer--a comprehensive strategy for de novo identification of DNA regulatory motifs at a genome level. Using word-counting methods, we indexed the existence of every 8-mer oligo composed of bases A, C, G, T, r, y, s, w, m, k, n or 12-mer oligo composed of A, C, G, T, n, in the promoters of all predicted genes of Arabidopsis thaliana genome and of selected stres ...[more]

PMID: 22912824

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Project description:Intricate signal networks and transcriptional regulators translate the recognition of pathogens into defense responses. In this study, we carried out a gene co-expression analysis of all currently publicly available microarray data, which were generated in experiments that studied the interaction of the model plant Arabidopsis thaliana with microbial pathogens. This work was conducted to identify (i) modules of functionally related co-expressed genes that are differentially expressed in response to multiple biotic stresses, and (ii) hub genes that may function as core regulators of disease responses. Using Weighted Gene Co-expression Network Analysis (WGCNA) we constructed an undirected network leveraging a rich curated expression dataset comprising 272 microarrays that involved microbial infections of Arabidopsis plants with a wide array of fungal and bacterial pathogens with biotrophic, hemibiotrophic, and necrotrophic lifestyles. WGCNA produced a network with scale-free and small-world properties composed of 205 distinct clusters of co-expressed genes. Modules of functionally related co-expressed genes that are differentially regulated in response to multiple pathogens were identified by integrating differential gene expression testing with functional enrichment analyses of gene ontology terms, known disease associated genes, transcriptional regulators, and cis-regulatory elements. The significance of functional enrichments was validated by comparisons with randomly generated networks. Network topology was then analyzed to identify intra- and inter-modular gene hubs. Based on high connectivity, and centrality in meta-modules that are clearly enriched in defense responses, we propose a list of 66 target genes for reverse genetic experiments to further dissect the Arabidopsis immune system. Our results show that statistical-based data trimming prior to network analysis allows the integration of expression datasets generated by different groups, under different experimental conditions and biological systems, into a functionally meaningful co-expression network.

Project description:Reactive oxygen species (ROS) generated endogenously or from exogenous sources produce mutagenic DNA lesions. If not repaired, these lesions could lead to genomic instability and, potentially, to cancer development. NEIL2 (EC 4.2.99.18), a mammalian base excision repair (BER) protein and ortholog of the bacterial Fpg/Nei, excises oxidized DNA lesions from bubble or single-stranded structures, suggesting its involvement in transcription-coupled DNA repair. Perturbation in NEIL2 expression may, therefore, significantly impact BER capacity and promote genomic instability. To characterize the genetic and environmental factors regulating NEIL2 gene expression, we mapped the human NEIL2 transcriptional start site and partially characterized the promoter region of the gene using a luciferase reporter assay. We identified a strong positive regulatory region from nucleotide -206 to +90 and found that expression from this region was contingent on its being isolated from an adjacent strong negative regulatory region located downstream (+49 to +710 bp), suggesting that NEIL2 transcription is influenced by both these regions. We also found that oxidative stress, induced by glucose oxidase treatment, reduced the positive regulatory region expression levels, suggesting that ROS may play a significant role in regulating NEIL2 transcription. In an initial attempt to characterize the underlying mechanisms, we used in silico analysis to identify putative cis-acting binding sites for ROS-responsive transcription factors within this region and then used site-directed mutagenesis to investigate their role. A single-base change in the region encompassing nucleotides -206 to +90 abolished the effect of oxidative stress that was observed in the absence of the mutation. Our study is the first to provide an initial partial characterization of the NEIL2 promoter and opens the door for future research aimed at understanding the role of genetic and environmental factors in regulating NEIL2 expression.

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Discovery of stress responsive DNA regulatory motifs in Arabidopsis.

Publications

Discovery of stress responsive DNA regulatory motifs in Arabidopsis.

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