Roles of the SKU genes in directional cell expansion

Illinois State University, Normal IL

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Abstract

DESCRIPTION (provided by applicant): When placed on an inclined agar surface, Arabidopsis roots grow downward in the shape of a sinusoidal wave. This so-called root-waving pattern of growth is in part the result of root tip responses to gravity and touch. To gain a better understanding of the underlying cell expansion processes, we identified numerous mutants with altered root waving growth habits. This proposal focuses on five of those mutants, which we named sku6 through sku10. These sku mutants have roots that grow at distinct angles from the normal downward waving direction. Additionally, at least three of these sku mutants have roots and/or hypocotyls that twist abnormally about their axes as they grow (sku6, sku7 and sku10). The root skewing phenotypes are surface dependent and due to touch-induced alterations in cell expansion patterns. Interestingly, at least three of the sku mutants exhibit altered root growth responses to either one of the anti-microtubule drugs propyzamide or dithiopyr, suggesting cytoskeleton involvement. Genetic analyses have shown that the sku mutations are recessive and affect separate genes. To date we have cloned the SKU6 gene, finding it encodes a predicted 12kD protein with no identifiable sequence homologies. The aims of this study are the following: 1) Make detailed measurements of various sku mutant growth phenotypes in order to better characterize the cell expansion alterations. These measurements will allow us to draw comparisons between the processes affected in the different sku mutants as well as delineate baseline growth parameters for drug studies and double mutant analysis. 2) Create and analyze double sku mutants in order to determine genetic interactions and build genetic pathways. 3) Use a tubulin-GFP reporter construct to visualize cortical microtubule arrays in single and double sku mutants in the presence and absence of anti-microtubule drugs. 4) Clone the sku genes. Further molecular analyses of these genes will be the focus of future studies. Together, these analyses should significantly increase our knowledge and understanding of how plants and perhaps other organisms direct cell expansion. They should also provide insights into mechanisms that control microtubule assembly and stability.