Genetic analysis of microRNA function in Arabidopsis thaliana development
Toups Dugas, Diana V.
Doctor of Philosophy
MicroRNAs (miRNAs) are 21-24-nucleotide RNAs that negatively regulate gene expression. Plant miRNAs play important roles in gene regulation by directing cleavage of target mRNAs. The high degree of complementarity between plant miRNAs and their target mRNAs has allowed rapid progress in identifying the targets of these small riboregulators, although much remains to be discovered about the biological roles of many miRNA:mRNA relationships. I analyzed the roles of miR170/171, miR398c, and miR164b in plant development. Like many plant miRNAs, the miR170/171 and miR164 families both target mRNAs encoding transcription factors. miR170/171 targets three uncharacterized GRAS-domain transcription factors, SCARECROW-like (SCL) 6-II, SCL6-III , and SCL6-IV mRNAs. I found that overexpressing miR170/171 in Arabidopsis results in altered shoot development, including reduced outgrowth of axillary meristems and alterations of meristem identity. miR164 targets six NAC-domain transcription factors, three of which had previously characterized roles in root and shoot development. I found that plants overexpressing miR164b display cotyledon, sepal, and stamen fusions reminiscent of mutants defective in two of the miR164 target genes. Plants overexpressing miR164b displayed additional vegetative fusions, including leaf-leaf and leaf-stem fusions, implicating additional NAC genes in vegetative organ separation. miR398 targets mRNAs encoding two copper superoxide dismutases and the cytochrome C oxidase subunit Vb, making it a member of the growing class of Arabidopsis miRNAs that target non-transcription factor mRNAs. Copper has been reported to negatively regulate miR398 accumulation. I found that miR398 is induced in plants grown on medium supplemented with sucrose and that miR398 accumulation is independently regulated by copper and sucrose. This work helped elucidate not only the roles of three miRNA families, but also the functions of some of the target mRNAs in Arabidopsis. Conservation of these miRNA families and their targets among flowering plants suggests that knowledge gained in Arabidopsis may be applicable across multiple species.
Genetics; Plant biology; Biological sciences; Plant development miRNAs