Résumé
The plant root system plays pivotal functions in soil foraging and water and nutrients supply to the whole organism. Plants survival and fitness under unfavorable growth conditions therefore highly depends on the root system adaptability that relies on its developmental plasticity via the combinatorial modulation of undetermined growth and branching. Glutaredoxins (GRXs) are generally known as thiol-disulfide proteins involved in the control of reactive oxygen species homeostasis, which is critical for plant survival and adaptation in response to changing environmental conditions. They also modulate the activity of several enzymes implicated in plant development, although quite little is known about their functions in root development. The ROXY family is a land plant-specific family of GRX (classIII GRX), composed of 21 members in Arabidopsis. All members harbor a Cys-Cys (CC) putative active site, and a L**LL motif important for binding to TGA transcription factors. Some of the ROXY also share a terminal ALWL motif important for binding to the TOPLESS (TPL) and TOPLESS RELATED (TPR) transcriptional co-repressors, which leads to ternary ROXY/TGA/TPL complexes. This suggests an important role of this family in transcriptional regulation of downstream pathways. Although mainly expressed in roots, ROXY19 has never been implicated in root development so far. In this work, we show that ROXY19 controls in opposite ways primary and lateral root growth in Arabidopsis thaliana, by modulating cell elongation. We also report that ROXY19 is required for proper root development responses to Abscisic Acid (ABA) treatments, thus suggesting a key role for this GRX in root system adaptation to water availability. A detailed transcriptomic analysis has been conducted to better understand the molecular mechanisms enabling ROXY19 to fine tune root system architecture under optimal conditions and in response to ABA.