Vascular Transcription Factor TMO5 Regulates PIN1 Polarity andOrganogenesis Downstream of MONOPTEROS in the Shoot Meristem

Plants continuously produce lateral organs, such as leaves and flowers, from the shoot apical meristem (SAM). This process is guided by the accumulation of the plant hormone auxin and the polar localization of the efflux protein PIN-FORMED1 (PIN1). The transcription factor MONOPTEROS (MP) plays a crucial role in orienting PIN1 polarity, thereby facilitating auxin-driven organogenesis. In this study, we investigated how MP regulates PIN1 polarity and organogenesis, discovering that the downstream vascular transcription factor TMO5 regulates PIN1 polarity non-cell-autonomously and promotes organ initiation in the SAM. Furthermore, we find that exogenous auxin and cytokinin can partially rescue the organ defects associated with loss of MP and TMO5 activity. Collectively, these findings uncover a novel role for TMO5 in controlling PIN1 polarity and driving organogenesis by coordinating hormonal signalling.