Advances in the study of auxin early response genes: Aux/IAA, GH3, and SAUR

Auxin plays a crucial role in all aspects of plant growth and development. Auxin can induce the rapid and efficient expression of some genes, which are named auxin early response genes (AERGs), mainly including the three families: auxin/indole-3-acetic acid (Aux/IAA), Gretchen Hagen 3 (GH3), and small auxin-up RNA (SAUR). Aux/IAA encodes the Aux/IAA protein, which is a negative regulator of auxin response. Aux/IAA and auxin response factor (ARF) form a heterodimer and participate in a variety of physiological processes through classical or non-classical auxin signaling pathways. The GH3 encodes auxin amide synthetase, which catalyzes the binding of auxin to acyl-containing small molecule substrates (such as amino acids and jasmonic acid), and regulates plant growth and stresses by regulating auxin homeostasis. SAURs is a class of small auxin up-regulated RNAs. SAUR response to auxin is complex, and the process may occur at the transcriptional, post-transcriptional and protein levels. With the development of multi-omics, significant progress has been made in the study of Aux/IAA, GH3, and SAUR genes, but there are still many unknowns. This review offers insight into the characteristics of Aux/IAA, GH3, and SAUR gene families, and their roles in roots, hypocotyls, leaves, leaf inclinations, flowers, seed development, stress response, and phytohormone crosstalk, and provides clues for future research on phytohormone signaling and the molecular design breeding of crops.