Spatial specificity of auxin responses coordinates wood formation

Klaus Brackmann,Jiyan Qi,Virginie Jouannet,Michael Gebert,Javier Agustí,Karin Grünwald,Daria D Novikova,Pablo Sanchez,Theresa Schlamp,Thomas Greb,Jan U Lohmann,Victor G Levitsky,Eva-Sophie Wallner

doi:10.1038/s41467-018-03256-2

Abstract

Spatial organization of signalling events of the phytohormone auxin is fundamental for maintaining a dynamic transition from plant stem cells to differentiated descendants. The cambium, the stem cell niche mediating wood formation, fundamentally depends on auxin signalling but its exact role and spatial organization is obscure. Here we show that, while auxin signalling levels increase in differentiating cambium descendants, a moderate level of signalling in cambial stem cells is essential for cambium activity. We identify the auxin-dependent transcription factor ARF5/MONOPTEROS to cell-autonomously restrict the number of stem cells by directly attenuating the activity of the stem cell-promoting WOX4 gene. In contrast, ARF3 and ARF4 function as cambium activators in a redundant fashion from outside of WOX4-expressing cells. Our results reveal an influence of auxin signalling on distinct cambium features by specific signalling components and allow the conceptual integration of plant stem cell systems with distinct anatomies.

Highlights

Spatial organization of signalling events of the phytohormone auxin is fundamental for maintaining a dynamic transition from plant stem cells to differentiated descendants
In Arabidopsis stems, the activity of the common auxin response marker pDR5rev:GFP30 was detected in vascular tissues and cortical cells prior and during cambium initiation (Fig. 1a, Supplementary Fig. 1a)[23]
To decide between both possibilities, we generated a plant line expressing an endoplasmatic reticulum (ER)-targeted Yellow Fluorescent Protein (YFP) under the control of the high-affinity DR5revV2 promoter, which recapitulated the pattern of DR5revV2 activity previously reported in roots (Supplementary Fig. 1d-f)[31]

Summary

Introduction

Spatial organization of signalling events of the phytohormone auxin is fundamental for maintaining a dynamic transition from plant stem cells to differentiated descendants. Consistent with a role of ARF activity in cambium regulation, Dex a d treatments of pPXY:Myc-GR-bdl plants resulted in a strongly reduced amount of ICD tissues at the stem base (Fig. 1i, j, m) but not in an altered overall growth habit (Supplementary Fig. 3h).

Results

Conclusion