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Title: A KINESIN-LIKE PROTEIN IS ESSENTIAL FOR ORIENTED DEPOSITION OF CELLULOSE MICROFIBRILS AND CELL WALL STRENGTH

Author
item ZHONG, RUIQIN - UNIV OF GEORGIA
item BURK, DAVID - UNIV OF GEORGIA
item MORRISON III, WILEY
item YE, ZHENG-HUA - UNIV OF GEORGIA

Submitted to: The Plant Cell
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/27/2002
Publication Date: 12/1/2002
Citation: ZHONG, R., BURK, D.H., MORRISON III, W.H., YE, Z. A KINESIN-LIKE PROTEIN IS ESSENTIAL FOR ORIENTED DEPOSITION OF CELLULOSE MICROFIBRILS AND CELL WALL STRENGTH. THE PLANT CELL. 2002. v. 14. p. 3101-3117.

Interpretive Summary: Plant cells are enclosed in a rigid cell wall that gives strength to the plant as it grows so that it will not break under its own weight. Special cell types encircle the fibers as the plant increases in length holding them together and providing strength. Understanding how the cell deposition is oriented along the growing plant provides an important insight into the process of cell specialization. A mutant gene was isolated and later cloned. It was then incorporated in a new plant to demonstrate its affect on the developing plant and allowed for the examination of the difference in fiber orientation as the plant matured. This work could play an important role in understanding why some plants 'lodge' or fall over in mild wind conditions thus reducing yields.

Technical Abstract: It has long been hypothesized that cortical microtubules (MTs) regulate the oriented deposition of cellulose microfibrils. However, the molecular mechanisms on how MTs direct the orientation of cellulose microfibril deposition are not known. We have used fibers in the inflorescence stems of Arabidopsis to study secondary wall deposition and cell wall strength, and found a fragile fiber (fra1) mutant with a dramatic reduction in the mechanical strength of fibers. The fra1 mutation did not cause any defects in cell wall composition, secondary wall thickening, or cortical MT organization in fiber cells. An apparent alteration was found in the orientation of cellulose microfibrils in fra1 fiber walls, indicating that the reduced mechanical strength of fra1 fibers was probably due to altered cellulose microfibril deposition. The fra1 mutation also caused a reduction in the elongation of inflorescence stems, etiolated hypocotyls, and primary roots. The FRA1 gene was cloned and shown to encode a kinesin-like protein with an N-terminus-located MT-binding motor domain. Based on these findings, we propose that the FRA1 kinesin-like protein is involved in the MT control of cellulose microfibril order.