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Plant Cell Advance Online Publication
Published on October 26, 2007; 10.1105/tpc.107.044354

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Received May 23, 2006
Returned for revision August 30, 2007
Accepted October 6, 2007

MPB2C, a Microtubule-Associated Protein, Regulates Non-Cell-Autonomy of the Homeodomain Protein KNOTTED1

Nikola Winter 1, Gregor Kollwig 1, Shoudong Zhang 1, and Friedrich Kragler 1*

1 Department of Biochemistry, University of Vienna, Vienna A-1030, Austria

* To whom correspondence should be addressed. E-mail: friedrich.kragler{at}univie.ac.at.

Plasmodesmata establish a pathway for the intercellular trafficking of viral movement proteins and endogenous non-cell-autonomous proteins, such as the two closely related meristem-maintaining KNOTTED1-like homeobox (KNOX) proteins Zea mays KNOTTED1 (KN1) and Arabidopsis thaliana SHOOTMERISTEMLESS (STM). KNOX family members are DNA binding proteins that regulate the transcriptional activity of target genes in conjunction with BEL1-like homeodomain proteins. It has been shown previously, using in vivo transport assays, that the C-terminal domain of KN1, including the homeodomain, is necessary and sufficient for cell-to-cell transport through plasmodesmata. Here, using interaction and coexpression assays, we demonstrate that the microtubule-associated and viral movement protein binding protein MPB2C from Nicotiana tabacum, and its homolog in Arabidopsis, At MPB2C, are KN1/STM binding factors. Interaction between the MPB2C proteins and KN1/STM was mapped to the KN1 homeodomain, a region not essential for heterodimerization with BEL1. Expression of MPB2C in single cells prevented KN1 cell-to-cell movement. Furthermore, in vivo trichome rescue studies established that MPB2C negatively regulates KN1 association to plasmodesmata and, consequently, cell-to-cell transport. These findings are discussed in terms of the role played by MPB2C proteins in regulating the cell-to-cell trafficking of homeodomain proteins in plants.




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N. Bolduc, S. Hake, and D. Jackson
Dual Functions of the KNOTTED1 Homeodomain: Sequence-Specific DNA Binding and Regulation of Cell-to-Cell Transport
Sci. Signal., June 10, 2008; 1(23): pe28 - pe28.
[Abstract] [Full Text] [PDF]


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