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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

MAP20, a Microtubule-Associated Protein in the Secondary Cell Walls of Hybrid Aspen, Is a Target of the Cellulose Synthesis Inhibitor 2,6-Dichlorobenzonitrile^1,[W],[OA]

Swedish Center of Biomimetic Fiber Engineering (A.S.R., H.A., G.G., P.P., C.J.-L.B., S.H., K.B., C.D., I.E., V.B., T.T.T.), and Stockholm Bioinformatics Center (L.A.), KTH-Royal Institute of Technology, AlbaNova, SE–10691 Stockholm, Sweden; and Umea Plant Science Center, Department of Forest Genetics and Plant Physiology, SE–90183 Umea, Sweden (M.K., B.S., E.M.)

We have identified a gene, denoted PttMAP20, which is strongly up-regulated during secondary cell wall synthesis and tightly coregulated with the secondary wall-associated CESA genes in hybrid aspen (Populus tremula x tremuloides). Immunolocalization studies with affinity-purified antibodies specific for PttMAP20 revealed that the protein is found in all cell types in developing xylem and that it is most abundant in cells forming secondary cell walls. This PttMAP20 protein sequence contains a highly conserved TPX2 domain first identified in a microtubule-associated protein (MAP) in Xenopus laevis. Overexpression of PttMAP20 in Arabidopsis (Arabidopsis thaliana) leads to helical twisting of epidermal cells, frequently associated with MAPs. In addition, a PttMAP20-yellow fluorescent protein fusion protein expressed in tobacco (Nicotiana tabacum) leaves localizes to microtubules in leaf epidermal pavement cells. Recombinant PttMAP20 expressed in Escherichia coli also binds specifically to in vitro-assembled, taxol-stabilized bovine microtubules. Finally, the herbicide 2,6-dichlorobenzonitrile, which inhibits cellulose synthesis in plants, was found to bind specifically to PttMAP20. Together with the known function of cortical microtubules in orienting cellulose microfibrils, these observations suggest that PttMAP20 has a role in cellulose biosynthesis.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instruction for Authors (www.plantphysiol.org) is: Tuula T. Teeri (tuula{at}biotech.kth.se).

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www.plantphysiol.org/cgi/doi/10.1104/pp.108.121913

^* Corresponding author; e-mail tuula{at}biotech.kth.se.

Received April 23, 2008; accepted September 16, 2008; published September 19, 2008.