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Genome-wide expression analysis and regulation of microRNAs and cis natural antisense transcripts in Arabidopsis thaliana

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Title: Genome-wide expression analysis and regulation of microRNAs and cis natural antisense transcripts in Arabidopsis thaliana
Author: Zhan, Shuhua
Department: Department of Plant Agriculture
Program: Bioinformatics
Advisor: Dr. Lukens, Lewis
Abstract: Small RNAs (sRNAs), circa 21-26nt RNA molecules, are a novel class of regulatory molecules that influence many aspects of plant biology. The first objective of this thesis was to utilize computational approaches both to investigate how microRNAs (miRNAs), a type of sRNA, as a class affect their target transcripts’ accumulation and to identify novel miRNAs in Arabidopsis thaliana. The second objective of this thesis was to examine the regulation of protein coding (PC) cis natural antisense transcripts (cis-NATs), which have the potential to make double stranded RNA. Computational analysis of the expression of miRNA-regulated genes demonstrated that the transcriptomes of the inflorescences of plants defective in miRNA biogenesis were similar to normal leaf tissues and dissimilar to normal pollen and seed. Thus, miRNAs cause the plant transcriptome to shift from a vegetative to reproductive state. Known miRNA targets fail to explain miRNA-defective mutant transcriptome patterns. Novel computational approaches were used to discover five new mature miRNAs. Interestingly, two miRNAs have different functions but are encoded by perfect complements of the same precursor molecule. Genome-wide analysis of cis-NAT abundances revealed that protein coding (PC) cis-NATs tend to be co-expressed, broadly expressed, and highly expressed across diverse abiotic stress conditions. These expression patterns were negatively associated with sRNAs because sRNAs were under-represented within PC cis-NATs compared to PC non-cis-NATs. sRNAs also mapped to cis-NATs and non-cis-NATs at similar frequencies in mutants defective in nat-siRNA biogenesis relative to other genotypes. We suggest a common euchromatin environment and possibly antisense RNA stabilization of mRNA transcripts may contribute to the high level, breadth, and co-expression of cis-NATs. However, cis-NATs are correlated less frequently than expected, and cis-NAT transcript abundances often differ more than expected. In addition, sRNAs matched PC cis-NATs relative to PC non-cis-NATs more frequently in abiotic stress conditions than in control conditions. Thus, although sRNAs do not have a widespread role in regulating cis-NATs, sRNAs may have a focused role in regulating cis-NAT transcript abundances.
Description: PhD thesis
Date: 2012-01
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