Theoretical approaches to understanding root vascular patterning: a consensus between recent models

Abstract

A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription. AbstractThe root vascular tissues provide an excellent system for studying organ patterning, as the specification of these tissues signals a transition from radial symmetry to bisymmetric patterns. The patterning process is controlled by the combined action of hormonal signaling/transport pathways, transcription factors, and miRNA that operate through a series of non-linear pathways to drive pattern formation collectively. With the discovery of multiple components and feedback loops controlling patterning, it has become increasingly difficult to understand how these interactions act in unison to determine pattern formation in multicellular tissues. Three independent mathematical models of root vascular patterning have been formulated in the last few years, providing an excellent example of how theoretical approaches can complement experimental studies to provide new insights into complex systems. In many aspects these models support each other; however, each study also provides its own novel findings and unique viewpoints. Here we reconcile these models by identifying the commonalities and exploring the differences between them by testing how transferable findings are between models. New simulations herein support the hypothesis that an asymmetry in auxin input can direct the formation of vascular pattern. We show that the xylem axis can act as a sole source of cytokinin and specify the correct pattern, but also that broader patterns of cytokinin production are also able to pattern the root. By comparing the three modeling approaches, we gain further insight into vascular patterning and identify several key areas for experimental investigation.

Realizing pipe dreams – a detailed picture of vascular development

“…There were some disagreements in the outputs, most notably around cytokinin gradients, indicating that further experiments are required. Nevertheless all three models support the interaction of auxin and cytokinin as a plausible system for generating early vascular pattern (Mellor et al , 2017). While these hormone interactions are responsible for generating pattern, they are underpinned by a network of interacting factors, dominated by helix-loop-helix transcription factors, TARGET OF MONOPTEROS 5 (TMO5) (Schlereth et al , 2010), LONESOME HIGHWAY (LHW) (Ohashi-Ito and Bergmann, 2007), SUPRESSOR OF ACAULIS51 (SAC51) (Imai et al , 2006), and SAC51-LIKE (SACL) (Cai et al , 2016), that act downstream of auxin signalling and influence cytokinin activity (reviewed in Campbell and Turner, 2017).…”

Plant vascular development: mechanisms and environmental regulation

“…As is the case during embryogenesis, the prevailing models propose that patterning is initially established by the interplay between high CK and high auxin levels, which define distinct domains in the root procambium [27].…”

Mechanism of Allium Crops Bulb Enlargement in Response to Photoperiod: A Review

“…In addition, cytokinin signaling in procambial cells affects auxin efflux through PIN-FORMED (PIN) protein expression and localization [111]. Mathematical modeling suggests that this interplay is sufficient to achieve bilateral symmetry within the vasculature [112][113][114][115]. Cytokinins are tightly linked to vascular development because classical mutants in the signaling pathway such as wooden leg (ahk4/cre1/wol) and ahp6 were identified because of their vascular defects.…”