Cytokinin as a positional cue regulating lateral root spacing in Arabidopsis.

Ling Chang,Thomas Schmülling,Eswarayya Ramireddy

doi:10.1093/jxb/erv252

Ling Chang, Thomas Schmülling + Show 1 more

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https://doi.org/10.1093/jxb/erv252

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Abstract

The root systems of plants have developed adaptive architectures to exploit soil resources. The formation of lateral roots (LRs) contributes to root system architecture. Roots of plants with a lower cytokinin status form LR primordia (LRP) in unusually close proximity, indicating a role for the hormone in regulating the positioning of LRs along the main root axis. Data obtained from cytokinin-synthesis mutants of Arabidopsis thaliana combined with gene expression analysis indicate that cytokinin synthesis by IPT5 and LOG4 occurring early during LRP initiation generates a local cytokinin signal abbreviating LRP formation in neighbouring pericycle cells. In addition, IPT3, IPT5, and IPT7 contribute to cytokinin synthesis in the vicinity of existing LRP, thus suppressing initiation of new LRs. Interestingly, mutation of CYP735A genes required for trans-zeatin biosynthesis caused strong defects in LR positioning, indicating an important role for this cytokinin metabolite in regulating LR spacing. Further it is shown that cytokinin and a known regulator of LR spacing, the receptor-like kinase ARABIDOPSIS CRINKLY4 (ACR4), operate in a non-hierarchical manner but might exert reciprocal control at the transcript level. Taken together, the results suggest that cytokinin acts as a paracrine hormonal signal in regulating root system architecture.

Highlights

Lateral roots (LRs) form the main part of plant root systems and are important to optimize the ability of a root system to acquire soil nutrients and water
Spaced lateral roots (LRs) primordia (LRP) mostly belonged to the same developmental stage or differed by just one stage, indicating that they were induced at a similar time (Fig. 1F,G)
The primary roots of acr4 mutants were only about 15% shorter than those of wild type and those of 35S:CKX1 transgenic plants were even longer (Werner et al, 2003), indicating that the shorter distance between LRP is not correlated with the length of the primary root

Summary

Introduction

Lateral roots (LRs) form the main part of plant root systems and are important to optimize the ability of a root system to acquire soil nutrients and water. Xylem pole PCs are developmentally primed to form competent sites for LR formation along the longitudinal axis This pre-pattern is established by an endogenous clock-like mechanism, termed the LR clock (Moreno-Risueno et al, 2010). Not all competent cells develop into LRP or LRs and the mechanisms patterning the local spacing of LRP remain largely uncharacterized.

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