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PLANTS INTERACTING WITH OTHER ORGANISMS

Microtubule-Associated Protein AtMPB2C Plays a Role in Organization of Cortical Microtubules, Stomata Patterning, and Tobamovirus Infectivity¹

Max F. Perutz Laboratories, University Departments at the Vienna Biocenter, Department of Medical Biochemistry, Medical University of Vienna, 1030 Vienna, Austria (P.R., D.F., E.W.); and Gregor Mendel Institute of Molecular Plant Biology, Austrian Academy of Sciences, 1030 Vienna, Austria (J.K., C.J.)

AtMPB2C is the Arabidopsis (Arabidopsis thaliana) homolog of MPB2C, a microtubule-associated host factor of tobacco mosaic virus movement protein that was been previously identified in Nicotiana tabacum. To analyze the endogenous function of AtMPB2C and its role in viral infections, transgenic Arabidopsis plant lines stably overexpressing green fluorescent protein (GFP)-AtMPB2C were established. The GFP-AtMPB2C fusion protein was detectable in various cell types and organs and localized at microtubules in a punctuate pattern or in filaments. To determine whether overexpression impacted on the cortical microtubular cytoskeleton, GFP-AtMPB2C-overexpressing plants were compared to known microtubular marker lines. In rapidly elongated cell types such as vein cells and root cells, GFP-AtMPB2C overexpression caused highly unordered assemblies of cortical microtubules, a disturbed, snake-like microtubular shape, and star-like crossing points of microtubules. Phenotypically, GFP-AtMPB2C transgenic plants showed retarded growth but were viable and fertile. Seedlings of GFP-AtMPB2C transgenic plants were characterized by clockwise twisted leaves, clustered stomata, and enhanced drought tolerance. GFP-AtMPB2C-overexpressing plants showed increased resistance against oilseed rape mosaic virus, a close relative of tobacco mosaic virus, but not against cucumber mosaic virus when compared to Arabidopsis wild-type plants. These results suggest that AtMPB2C is involved in the alignment of cortical microtubules, the patterning of stomata, and restricting tobamoviral infections.

The author responsible for the distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Elisabeth Waigmann (elisabeth.waigmann{at}meduniwien.ac.at).

www.plantphysiol.org/cgi/doi/10.1104/pp.108.130450

^* Corresponding author; e-mail elisabeth.waigmann{at}meduniwien.ac.at.

Received September 26, 2008; accepted November 25, 2008; published December 12, 2008.