Journal Article

PINOID Kinase Regulates Root Gravitropism through Modulation of PIN2-Dependent Basipetal Auxin Transport in Arabidopsis

Sukumar, Poornima, Edwards, Karin S, Muday, Gloria K, Rahman, Abidur, DeLong, Alison

2009

Overview

Reversible protein phosphorylation is a key regulatory mechanism governing polar auxin transport. We characterized the auxin transport and gravitropic phenotypes of the pinoid-9 (pid-9) mutant of Arabidopsis (Arabidopsis thaliana) and tested the hypothesis that phosphorylation mediated by PID kinase and dephosphorylation regulated by the ROOTS CURL IN NAPHTHYLPHTHALAMIC ACID1 (RCN1) protein might antagonistically regulate root auxin transport and gravity response. Basipetal indole-3-acetic acid transport and gravitropism are reduced in pid-9 seedlings, while acropetal transport and lateral root development are unchanged. Treatment of wild-type seedlings with the protein kinase inhibitor staurosporine phenocopies the reduced auxin transport and gravity response of pid-9, while pid-9 is resistant to inhibition by staurosporine. Staurosporine and the phosphatase inhibitor, cantharidin, delay the asymmetric expression of DR5::revGFP (green fluorescent protein) at the root tip after gravistimulation. Gravity response defects of rcn1 and pid-9 are partially rescued by treatment with staurosporine and cantharidin, respectively. The pid-9 rcn1 double mutant has a more rapid gravitropic response than rcn1. These data are consistent with a reciprocal regulation of gravitropism by RCN1 and PID. Furthermore, the effect of staurosporine is lost in pinformed2 (pin2). Our data suggest that reduced PID kinase function inhibits gravitropism and basipetal indole-3-acetic acid transport. However, in contrast to PID overexpression studies, we observed wild-type asymmetric membrane distribution of the PIN2 protein in both pid-9 and wild-type root tips, although PIN2 accumulates in endomembrane structures in pid-9 roots. Similarly, staurosporine-treated plants expressing a PIN2::GFP fusion exhibit endomembrane accumulation of PIN2::GFP, but no changes in membrane asymmetries were detected. Our data suggest that PID plays a limited role in root development; loss of PID activity alters auxin transport and gravitropism without causing an obvious change in cellular polarity.

• Publisher: American Society of Plant Biologists
• Subject: Arabidopsis / Arabidopsis - cytology / Arabidopsis - drug effects / Arabidopsis - enzymology / Arabidopsis Proteins / Arabidopsis Proteins - metabolism / Arabidopsis thaliana / Auxins / Biological and medical sciences / Biological Transport / cantharidin / Cantharidin - pharmacology / Cell Membrane / Cell Membrane - drug effects / Cell Membrane - metabolism / Cell Polarity / Cell Polarity - drug effects / cytology / dephosphorylation / Development and Hormone Action / drug effects / enzymology / Fundamental and applied biological sciences. Psychology / Gene expression regulation / genetics / Gravitation / Gravitropism / Gravitropism - drug effects / Gravitropism - physiology / gravity / green fluorescent protein / Green Fluorescent Proteins / Green Fluorescent Proteins - metabolism / growth & development / indole acetic acid / Indoleacetic Acids / Indoleacetic Acids - metabolism / metabolism / Movements / mutants / Mutation / Mutation - genetics / pharmacology / Phosphatases / Phosphoric Monoester Hydrolases / Phosphoric Monoester Hydrolases - metabolism / Physiological regulation / physiology / Plant physiology and development / Plant Roots / Plant Roots - enzymology / Plant Roots - growth & development / Plant Roots - physiology / Plants / protein phosphorylation / Protein Serine-Threonine Kinases / Protein-Serine-Threonine Kinases - metabolism / Recombinant Fusion Proteins / Recombinant Fusion Proteins - metabolism / Retraining / Root tips / Seedlings / Staurosporine / Staurosporine - pharmacology / Suppression, Genetic / Suppression, Genetic - drug effects