| Brassinosteroids (BRs), whose structural counterparts in animals are steroid hormones, represent a class of plant hormones essential for normal plant growth and development. In order to have a more detailed understanding of BR action in the process of plant cell division, changes at physiological and molecular levels in selected test systems after BR treatment were analyzed in this study. We found that BR was not only able to increase bean (Phaseolus vulagris L.) cell number 1.7-fold after 24 hours, but also to increase the ratio of bean cell dry weight to wet weight after six days of treatment. Subtractive hybridization, in bean cell suspension cultures treated with or without BR, revealed four clones with sequence identity to Arabidopsis histone H2B, soybean high mobility group protein HMG1, Escherichia coli acyl carrier protein (ACP), and Arabidopsis TGF receptor interacting protein (Trip-1).;Due to the importance of Trip-1 in human development and yeast growth, further characterization of Trip-1 using bean cell suspension cultures and Arabidopsis as model systems was performed. The study of spatial and temporal expression patterns of Trip-1 in Arabidopsis plants showed that it was expressed in all tested organs through the major developmental stages, with the highest level in roots and flowers. The induction of Trip-1 by BR was not sensitive to a protein synthesis inhibitor, cycloheximide. To examine the function of Trip-1 in plant growth and development, sense overexpression and antisense inhibition techniques were employed. While the majority of sense transgenic Arabidopsis plants showed normal growth and phenotype, some of the sense plants did show greater vigor. The overall characteristic of surviving antisense transgenic plants was their delayed development at every stage of growth, culminating in the setting of abnormal siliques and seeds. Northern analysis using strand specific probes showed a good correlation between antisense mRNA levels and growth inhibition.;Both H2B and HMG1 are associated with replication of chromatin occurring during S phase of the cell cycle. Although the role of ACPs in cell division remains to be elucidated, their known function as protein cofactors in fatty acid synthesis may point to an importance in rapid cell division. While the importance of Trip-1 in cell cycle progress in yeast and in a growth factor signaling in human has been documented, the analysis of antisense transgenic Arabidopsis plants indicated a possible involvement of Trip-1 in the signaling of plant pattern formation. The effects of BR on these genes under different conditions indicated that besides auxin and cytokinin, BRs may play an important role in the kinetics of the cell cycle and in regulating the expression of genes associated with cell division events. (Abstract shortened by UMI.). |
