A phosphorylation-based switch controls TAA1-mediated auxin biosynthesis in plants

Qian Wang,Liyuan Yang,Yangtao Gu,Guochen Qin,Tongda Xu,Zhejun Zeng,Yongqiang Yu,Weiman Xing,Yuming He,Min Cao,Rong Chen,W Andy Tao

doi:10.1038/s41467-020-14395-w

Abstract

Auxin determines the developmental fate of plant tissues, and local auxin concentration is precisely controlled. The role of auxin transport in modulating local auxin concentration has been widely studied but the regulation of local auxin biosynthesis is less well understood. Here, we show that TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS (TAA1), a key enzyme in the auxin biosynthesis pathway in Arabidopsis thaliana is phosphorylated at Threonine 101 (T101). T101 phosphorylation status can act as an on/off switch to control TAA1-dependent auxin biosynthesis and is required for proper regulation of root meristem size and root hair development. This phosphosite is evolutionarily conserved suggesting post-translational regulation of auxin biosynthesis may be a general phenomenon. In addition, we show that auxin itself, in part via TRANS-MEMBRANE KINASE 4 (TMK4), can induce T101 phosphorylation of TAA1 suggesting a self-regulatory loop whereby local auxin signalling can suppress biosynthesis. We conclude that phosphorylation-dependent control of TAA1 enzymatic activity may contribute to regulation of auxin concentration in response to endogenous and/or external cues.

Highlights

Auxin determines the developmental fate of plant tissues, and local auxin concentration is precisely controlled
We found TAA1T101A proteins exhibited similar or even higher enzymatic activity compared with TAA1WT only when pyridoxal phosphate (PLP) cofactors were present in a sufficient amount in the assay (Fig. 1c, d; Supplementary Fig. 2a, b)
Under PLP-deficient conditions, neither TAA1T101A or TAA1T101D proteins showed normal enzymatic activity due to an abnormal ability to capture PLP from E. coli which is distinct from E. coli-purified TAA1WT proteins that are already bound to PLP16 (Supplementary Fig. 2a–c)

Summary

Introduction

Auxin determines the developmental fate of plant tissues, and local auxin concentration is precisely controlled. T101 phosphorylation status can act as an on/off switch to control TAA1-dependent auxin biosynthesis and is required for proper regulation of root meristem size and root hair development. This phosphosite is evolutionarily conserved suggesting posttranslational regulation of auxin biosynthesis may be a general phenomenon. Nutrition signals, such as glucose and nitrate induce auxin production by the transcriptional regulation of YUC2/8/9 and TAA1/TAR2, respectively, to regulate root growth[21,22,23,24] Environmental stresses, such as aluminum can modulate root architecture through the control of auxin levels via modulation of TAA1 gene transcription[25]. TRANS-MEMBRANE KINASE 4 (TMK4), a kinase in auxin signalling, targets to this phosphorylation site on TAA1 protein, which contributes to the modulation of auxin concentration during plant development

Methods

Results

Conclusion