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The Arabidopsis SKU6/SPIRAL1 Gene Encodes a Plus End-Localized Microtubule-Interacting Protein Involved in Directional Cell Expansion
John C. Sedbrook, David W. Ehrhardt, Sarah E. Fisher, Wolf-Rüdiger Scheible and Chris R. Somerville
The Plant Cell
Vol. 16, No. 6 (Jun., 2004), pp. 1506-1520
Published by: American Society of Plant Biologists (ASPB)
Stable URL: http://www.jstor.org/stable/3872233
Page Count: 15
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The sku6-1 mutant of Arabidopsis thaliana exhibits altered patterns of root and organ growth. sku6 roots, etiolated hypocotyls, and leaf petioles exhibit right-handed axial twisting, and root growth on inclined agar media is strongly right skewed. The touch-dependent sku6 root skewing phenotype is suppressed by the antimicrotubule drugs propyzamide and oryzalin, and right skewing is exacerbated by cold treatment. Cloning revealed that sku6-1 is allelic to spiral1-1 (spr1-1). However, modifiers in the Columbia (Col) and Landsberg erecta (Ler) ecotype backgrounds mask noncomplementation in sku6-1 (Col)/spr1-1 (Ler) F1 plants. The SPR1 gene encodes a plant-specific 12-kD protein that is ubiquitously expressed and belongs to a six-member gene family in Arabidopsis. An SPR1:green fluorescent protein (GFP) fusion expressed in transgenic seedlings localized to microtubules within the cortical array, preprophase band, phragmoplast, and mitotic spindle. SPR1:GFP was concentrated at the growing ends of cortical microtubules and was dependent on polymer growth state; the microtubule-related fluorescence dissipated upon polymer shortening. The protein has a repeated motif at both ends, separated by a predicted rod-like domain, suggesting that it may act as an intermolecular linker. These observations suggest that SPR1 is involved in microtubule polymerization dynamics and/or guidance, which in turn influences touch-induced directional cell expansion and axial twisting.
The Plant Cell © 2004 American Society of Plant Biologists (ASPB)