For many years, research has been carried out with the aim of understanding the mechanism of auxin action, its biosynthesis, catabolism, perception, and transport. One central interest is the auxin-dependent gene expression regulation mechanism involving AUXIN RESPONSE FACTOR (ARF) transcription factors and their repressors, the AUXIN/INDOLE-3-ACETIC ACID (Aux/IAA) proteins. Numerous studies have been focused on MONOPTEROS (MP)/ARF5, an activator of auxin-dependent gene expression with a crucial impact on plant development. This review summarizes over 30 years of research on MP/ARF5. We indicate the available analytical tools to study MP/ARF5 and point out the known mechanism of MP/ARF5-dependent regulation of gene expression during various developmental processes, namely embryogenesis, leaf formation, vascularization, and shoot and root meristem formation. However, many questions remain about the auxin dose-dependent regulation of gene transcription by MP/ARF5 and its isoforms in plant cells, the composition of the MP/ARF5 protein complex, and, finally, all the genes under its direct control. In addition, information on post-translational modifications of MP/ARF5 protein is marginal, and knowledge about their consequences on MP/ARF5 function is limited. Moreover, the epigenetic factors and other regulators that act upstream of MP/ARF5 are poorly understood. Their identification will be a challenge in the coming years.
Keywords: Arabidopsis thaliana; auxin; embryogenesis; flowering; meristem; plant; transcription factor; vascularization.
© The Author(s) 2023. Published by Oxford University Press on behalf of the Society for Experimental Biology.