Abstract
Directional growth of roots is a complex process that is modulated by various environmental signals. This work shows that presence of glucose (Glc) in the medium also extensively modulated seedling root growth direction. Glc modulation of root growth direction was dramatically enhanced by simultaneous brassinosteroid (BR) application. Glc enhanced BR receptor BRASSINOSTEROID INSENSITIVE1 (BRI1) endocytosis from plasma membrane to early endosomes. Glc-induced root deviation was highly enhanced in a PP2A-defective mutant, roots curl in naphthyl phthalamic acid 1-1 (rcn1-1) suggesting that there is a role of phosphatase in Glc-induced root-growth deviation. RCN1, therefore, acted as a link between Glc and the BR-signalling pathway. Polar auxin transport worked further downstream to BR in controlling Glc-induced root deviation response. Glc also affected other root directional responses such as root waving and coiling leading to altered root architecture. High light intensity mimicked the Glc-induced changes in root architecture that were highly reduced in Glc-signalling mutants. Thus, under natural environmental conditions, changing light flux in the environment may lead to enhanced Glc production/response and is a way to manipulate root architecture for optimized development via integrating several extrinsic and intrinsic signalling cues.
Highlights
The ability for plant organs to guide their growth at a specified angle from the gravity vector ensures that the shoot is positioned to maximize its light-harvesting capabilities and that the roots are positioned downward so as to maximize the uptake of water and nutrients
Glcinduced root deviation was highly enhanced in a PP2A-defective mutant, roots curl in naphthyl phthalamic acid 1-1 suggesting that there is a role of phosphatase in Glc-induced root-growth deviation
To check if this root directional response was a direct effect of light, the Glc-induced root deviation was studied in darkness
Summary
The ability for plant organs to guide their growth at a specified angle from the gravity vector (gravitropism) ensures that the shoot is positioned to maximize its light-harvesting capabilities and that the roots are positioned downward so as to maximize the uptake of water and nutrients. Auxin signalling and distribution is the most widely studied phenomenon in response to root gravitropism. Cytokinin plays a regulatory role in root gravitropism. Ethylene negatively regulates root gravitropism in an ETHYLENE RESISTANT1 (ETR1) and ETHYLENE INSENSITIVE2 (EIN2) -dependent manner; ethylene inhibits gravity response by altering flavonoid synthesis (Buer et al, 2006). Recent reports have shown that abscisic acid (ABA) acts as a negative regulator of gravitropic response in Arabidopsis roots (Han et al, 2009). The negative effect of ABA is a result of change in ionic
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