Fungal VOCs regulate the expression of WOX5 at the root meristem of plants under osmotic stress in Arabidopsis and Populus tremuloides seedlings

Communication between plants and fungi occurs even before direct physical contact via various chemical signaling pathways, among them, volatile organic compounds (VOCs). Fungal VOCs, including those emitted by ectomycorrhizal and symbiotic endophytic fungi, significantly influence plant development and root architecture. However, the molecular signaling mechanisms underlying its regulation remain unknown. The quiescent center (QC), located within the primary root meristem, serves as a reservoir of stem cells that generate daughter cells and constituting a key regulatory site for architectural modulation. These daughter cells either divide or differentiate to form the transition zone, maintaining a crucial balance for root meristem homeostasis. WOX5, a homeobox transcription factor expressed predominantly in the QC, regulates surrounding stem cells by repressing their differentiation, thereby preserving the stem cell niche and is essential for root meristem integrity. In this study, we aimed to analyze the effects of fungal VOCs emitted by Laccaria bicolor, Hebeloma cylindrosporum, and Serendipita indica on the root architecture and meristem regulation in Arabidopsis thaliana and Populus tremuloides. Our results demonstrate the impact of these fungal VOCs on the root architecture of both species and underline the importance of WOX5 regulation mediated by fungal VOCs for maintaining root meristem homeostasis.