AtMYB50 regulates root cell elongation by upregulating PECTIN METHYLESTERASE INHIBITOR 8 in Arabidopsis thaliana

Plant root development is regulated by several signal transduction pathways. Among them, plant phytohormones, like auxin and cytokinin, are well characterized for their molecular mechanisms of action. Reactive oxygen species (ROS) play important roles as signaling molecules in controlling root development. Under these signal transduction pathways, the gene regulatory network, which is controlled by transcription factors, is the key to regulating root growth. We have previously reported an important transcription factor, UP BEAT1 (UPB1), that regulates ROS homeostasis at the root tip, further controlling the transition from cell proliferation to differentiation. Although UPB1 directly regulates the expression of several peroxidases that control ROS homeostasis, UPB1 still targets genes other than peroxidases. This indicates that UPB1 may regulate root growth through different ROS signals. Here, we investigated the function of the transcription factor MYB50, a direct target of UPB1, in Arabidopsis thaliana. We then examined whether UPB1 regulates MYB50 expression in the roots using an induction expression system and imaging of multiple fluorescent proteins. We also performed RNA-Seq analysis using MYB50 estradiol induction lines and ChIP-seq analysis to identify the MYB50 regulatory gene network. Integrating these analyses with UPB1 regulatory network revealed that MYB50 regulates the expression of PECTIN METHYLESTERASE INHIBITOR 8 (PMEI8). These data suggest that MYB50 is a new root growth regulator under the UPB1 gene regulatory network, which differs from the control of ROS homeostasis. Our study presents a model including a new transcriptional network under MYB50 into UPB1 regulatory root growth system and will provide novel insights into the cell elongation controlled by pectin modification.