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Poster: Cell Walls and Cytoskeleton

239:Regulation and localization of an expansin protein in soybean.

Authors:Downes, Brian, P.(A)Steinbaker, C., Ryan.(A)Crowell, Dring, N.(A)
Affiliations:(A): Indiana University-Purdue University at Indianapolis
Presenter:Downes, Brian P., bddownes@iupui.edu

The cytokinin-induced message Cim1 accumulates 20-60 fold after treatment of a cytokinin-starved soybean suspension culture with cytokinin for 4 hours and occurs, in large part, by a posttranscriptional mechanism. Furthermore, sequence analysis indicates that Cim1 is 20-30 % identical to various members of the expansin gene family. In this report, we examine the regulation and localization of the Cim1 protein product. Cytokinin and auxin affected Cim1 protein accumulation. Western analysis of cytokinin-depleted soybean suspension cultured cells treated with cytokinin revealed increased levels of Cim1 protein 10-24 hours after treatment, which corresponds well to the cytokinin-induced accumulation of Cim1 mRNA after 4 hours. Interestingly, auxin also regulated the accumulation of the Cim1 protein. Cells depleted of both cytokinin and auxin showed a modest, but rapid, accumulation of Cim1 when treated with auxin alone (3-6 hrs), a pronounced, but delayed, accumulation of Cim1 when treated with cytokinin alone (20+hrs), and a large, rapid accumulation of Cim1 when treated with both hormones. In addition, the processing of Cim1 appears to have been altered by cytokinin and/or auxin treatment. Western analysis of fractionated soybean suspension cultured cells revealed that the Cim1 protein is in the cell wall. Cim1 can be extracted from purified wall fragments or obtained directly from the cell walls of intact cells. The presence of Cim1 in the cell wall is consistent with its predicted role as a cell wall loosening protein. We are currently investigating the effect of cytokinin and auxin treatment on protoplast wall regeneration and rigidity, and the corresponding accumulation of Cim1.

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