Auxin in plant growth and stress responses

Abstract

The phytohormone auxin has long been recognized for its essential role in plant growth and development. Recent advance indicated that auxin also plays critical roles in plant responses to environmental stresses. This has prompted investigation into molecular control of auxin homeostasis and plant growth in response to developmental and environmental stimuli. A simple two-step biosynthesis pathway from tryptophan to auxin has been defined. At its sites of action, three auxin receptor or co-receptor systems have been identified. Binding of auxin by ABP1 regulates ROP-GTPase-mediated gene expression and subcellular protein trafficking. Auxin perception by TIR1/AFB-Aux/IAA co-receptor and SKP2A activate auxin signaling and promote cell growth and cell division, respectively. Recent findings indicate that ABP1 functions upstream of TIR1/AFBs and negatively regulates the TIR1/AFB-Aux/IAA-mediated auxin signaling pathway, highlighting coordinate regulation of the signaling pathways mediated by different auxin receptor/co-receptors during plant growth and development. Recent advance reveals that environmental signals, such as high salinity and drought, induce modulations of auxin biosynthesis and the signaling pathway allowing for efficient cellular reprogramming of plant growth and development under stress. Research advance in auxin homeostatic control and response has led to success in manipulation of auxin biosynthesis and the signaling for improvement crops with desired agricultural traits.