PhD defense: Miranda van Wonterghem

Non-coding RNA in Arabidopsis. Discovery of nuclear ncRNAs from body methylated genes and of miRNA pathway inhibition by conserved, bacterial virulence factor

Supervisor
Peter Brodersen, Associate Professor, University of Copenhagen

Exam Committee
Jean Molinier, Dr., CNRS, Institut de Biologie Moléculaire des Plantes
Stefan Hoth, Professor and Dr., Universität Hamburg Fakultät für Mathematik, Informatik und Naturwissenschaften
Jan Christiansen, Associate Professor at University of Copenhagen

Abstract
This work evolves around elucidating the mechanisms of micro RNAs (miRNAs) in Arabidopsis thaliana. I identified a new class of nuclear non-coding RNAs derived from protein coding genes. The genes are miRNA targets with extensive gene body methylation. The RNA species are nuclear localized and despite lacking caps and poly-adenylation they are stable, which suggests that they are functional. In a second project I discovered that a conserved bacterial effector protein (HopX1) interacts with, and possibly degrades, a plant protein (MAD6) required for miRNA-guided repression of translation. The induction of the bacterial effector in plants results in defects in the miRNA activity comparable to the mutation of the MAD6 gene. Thus, the effector enables the bacterium to manipulate the essential miRNA pathway of the plant host.