Cell kinetics of auxin transport and activity in Arabidopsis root growth and skewing

Yangjie Hu,Or Megides,Yun Hu,Qingguo Chen,Ilan Tsarfaty,Ohad Doron,Zhaojun Ding,Eilon Shani,Ori Chekli,Moutasem Omary,Lukas Hoermayer,Jiří Friml,Yunde Zhao

doi:10.1038/s41467-021-21802-3

Abstract

Auxin is a key regulator of plant growth and development. Local auxin biosynthesis and intercellular transport generates regional gradients in the root that are instructive for processes such as specification of developmental zones that maintain root growth and tropic responses. Here we present a toolbox to study auxin-mediated root development that features: (i) the ability to control auxin synthesis with high spatio-temporal resolution and (ii) single-cell nucleus tracking and morphokinetic analysis infrastructure. Integration of these two features enables cutting-edge analysis of root development at single-cell resolution based on morphokinetic parameters under normal growth conditions and during cell-type-specific induction of auxin biosynthesis. We show directional auxin flow in the root and refine the contributions of key players in this process. In addition, we determine the quantitative kinetics of Arabidopsis root meristem skewing, which depends on local auxin gradients but does not require PIN2 and AUX1 auxin transporter activities. Beyond the mechanistic insights into root development, the tools developed here will enable biologists to study kinetics and morphology of various critical processes at the single cell-level in whole organisms.

Highlights

Auxin is a key regulator of plant growth and development
Since our results indicate that root skewing is regulated by auxin gradients, we tested whether PIN2 or AUX1 is required for this process. pin[2] and aux[1] mutant seedlings have skewing angles similar to that of the control (Fig. 6g, h, Supplementary Fig. 16), and single-cell X and Z velocity scatter plots showed no difference between pin[2] and aux[1] mutant seedlings compared to controls
Space flight research suggests that the force of gravity is not needed for waving and skewing patterns of Arabidopsis roots grown on solid surfaces[54]

Summary

Introduction

Auxin is a key regulator of plant growth and development. Local auxin biosynthesis and intercellular transport generates regional gradients in the root that are instructive for processes such as specification of developmental zones that maintain root growth and tropic responses. The auxin gradients are primarily established by local auxin biosynthesis and the combined activities of auxin influx and efflux carrier proteins[11] It is not entirely clear which cell types produce IAA, recent studies have shown that the tryptophan aminotransferase TAA1 ( known as WEI8), TAR2 enzymes, which convert tryptophan to indole-3-pyruvic acid, and YUCCA enzymes, which convert indole-3-pyruvic acid to bioactive IAA12–15 are required for tightly controlled auxin levels and root meristem maintenance[16,17]. We used an inducible multi-cell-type-specific auxin biosynthesis system and custom image-analysis tools to quantitatively characterize auxin movement and activity in high spatial and temporal resolution, shedding light on auxin-dependent kinetic parameters of root growth and skewing

Methods

Results

Conclusion