Expression And Regulation Of Small RNAs In The Symbiosis Between Leguminous Plants And Microorganisms

This thesis focuses on small RNAs (sRNAs) that take part in the symbiosis between leguminous plants and microorganisms. Studies on the sequence characteristics, generation mechanism and biological function of the sRNAs were done by employing bioinformatics methods. The main research contents and results are summarized as follows:1. Based on the small RNA sequencing data of root nodules, arbuscular mycorriza and their controls in Medicago truncatula, soybean, peanut and common bean, twelve homologous miRNAs were identified in peanut and common bean, and these miRNAs were found to be conservative in different leguminous plants. By comparing the expression level of miRNAs in root nodules and arbuscular mycorriza, we found that miR160a/b and miR482were up-regulated in root nodules, nine miRNAs (miR169, miR171e, miR171g/h, miR2119, miR397, miR5204, miR5206, miR5229and miR5559) were down-regulated in root nodules but up-regulated or unchanged in arbuscular mycorriza, and miR160c/f and miR5229had no differences in root nodules while were up-regulated in arbuscular mycorriza. All of these results suggested that only a few miRNAs played the same roles in two conditions and the regulation of most miRNAs was different in the two symbiotic relationships.2. Based on the small RNA sequencing data of root nodules and arbuscular mycorriza in M. truncatula, the tRNA-derived small RNAs, namely tRFs, were detected in root nodules, arbuscular mycorriza and their controls. The characteristics and roles of these tRFs were investigated. The results showed that the tRNAs producing tRFs were not the same in different species, and environmental stresses had obvious effects on tRNA split. The production of tRFs was tRNA-specific, which was related to the sequences in the D/T loops rather than the anticodon loop in tRNAs. Besides, the location of tRNA gene in chromosome also had some impacts on tRF generation. The target genes of tRFs were predicted and most of them belonged to the ontology type of biological process. 3. By utilizing the same sRNA sequencing data as in2, some small rDNA-derived RNAs (srRNAs) were detected. Most srRNAs originated from18S rRNA and the others were from5.8S and25S rRNA. The cleavage of rRNAs had no obvious connection with external environment, and the srRNAs were generated from the less conservative region with loop-stem structure in rRNA precursor. We found that U-box domain ubiquitin ligase E3was the common target of srRNA, tRF and miRNA. There were complex interactions among the proteins encoded by target genes of these sRNAs. These results indicated that the sRNAs participated in the overall regulation of plant growth or some specific life process, not just in a single metabolic or signaling pathway.Through the above research, I hope my studies could partially expand the current understanding of regulatory mechanism in the symbiotic process between leguminous plants and microorganisms, and inspire further in-depth studies on plant non-coding RNAs.