Minisymposium 27: Growth & Vegetative Development

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Abs # M2704: Heterotrimeric G-proteins and two seven-transmembrane domain MLO proteins modulate light-regulated asymmetrical root growth

Presenter:	Chen, Zhongying       Contact Presenter
Authors	Chen, Zhongying  (A)   Hartmann, Andreas H. (B)   Panstruga, Ralph  (B)   Jones, Alan M. (A) (C)
Affiliations:	(A): Department of Biology, The University of North Carolina at Chapel Hill (B): Department of Plant-Microbe Interactions, Max-Planck Institute for Plant Breeding Research (C): Departments of Pharmacology, The University of North Carolina at Chapel Hill

Arabidopsis has a single canonical Gα (GPA1), one Gβ (AGB1) and two Gγ subunits of the heterotrimeric G-proteins. In animals, G-proteins regulate aspects of growth and development through ligand-activated seven-transmembrane (7TM) domain G-protein-coupled receptors. The largest 7TM domain protein family in Arabidopsis consist of 15 MLO proteins. Three closely-related MLO genes, MLO4, MLO11 and MLO14, have overlapping expression in root tips. Relative to wild type plants, loss-of-function alleles of mlo4 or mlo11, but not of mlo14, exhibited a dramatically enhanced asymmetrical root growth, manifested as a tight circling pattern on horizontal surfaces. In contrast, loss-of-function alleles of gpa1 or agb1 displayed significantly less root curling than wild type. Light and gravity are known external stimuli determining root growth patterns on horizontal surfaces (Mirza, 1987). In dark, mlo4, mlo11, gpa1 and agb1 seedlings exhibited wild-type levels of asymmetrical root growth, whereas roots of the gravity insensitive mutants, adg1 and pgm1, curled less. These results demonstrate that MLO4, MLO11 and G-proteins modulate light-regulation of intensity and/or direction of horizontal root curvature. Under light, photoreceptor mutants phot1 and cry1 showed decreased levels of root curvature, whereas phot2 and cry2 mutants exhibited increased root curling, suggesting that light induces counteracting signals through corresponding receptors. Double mutants agb1 mlo4, gpa1 mlo4, agb1 mlo11 and gpa1 mlo11 exhibited intermediate levels of horizontal root curvature. Therefore, 7TM domain proteins MLO4 and MLO11 likely function independent or downstream of heterotrimeric G-proteins in modulating light-regulated asymmetrical root growth.