Abstract
We investigated the role of ethylene and auxin in regulating the growth and morphology of roots during mechanical impedance by developing a new growing system and using the model plant Arabidopsis (Arabidopsis thaliana). The Arabidopsis seedlings grown horizontally on a dialysis membrane-covered agar plate encountered adequate mechanical impedance as the roots showed characteristic ethylene phenotypes: 2-fold reduction in root growth, increase in root diameter, decrease in cell elongation, and ectopic root hair formation. The root phenotype characterization of various mutants having altered response to ethylene biosynthesis or signaling, the effect of ethylene inhibitors on mechanically impeded roots, and transcription profiling of the ethylene-responsive genes led us to conclude that enhanced ethylene response plays a primary role in changing root morphology and development during mechanical impedance. Further, the differential sensitivity of horizontally and vertically grown roots toward exogenous ethylene suggested that ethylene signaling plays a critical role in enhancing the ethylene response. We subsequently demonstrated that the enhanced ethylene response also affects the auxin response in roots. Taken together, our results provide a new insight into the role of ethylene in changing root morphology during mechanical impedance.
Highlights
In nature, plant roots navigate through barriers in the soil
In an effort to understand the effect of continuous mechanical stimulation on Arabidopsis root morphology, we developed a new growing system that provides this stimulation continuously to root tips
When wild-type Arabidopsis seedlings were placed on dialysis membrane-covered agar plates, the roots grew in the horizontal direction without penetrating into the agar
Summary
Plant roots navigate through barriers in the soil. Responses of roots to mechanical perturbation are integral features of plant behavior. In contrast to the wild type, the horizontally grown ein2-1 roots showed a similar growth pattern and morphology like the vertical ones (Fig. 3).
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