The role of SPY and its TPR domain in the regulation of gibberellin action throughout the life cycle of Petunia hybrida plants
Article first published online: 23 DEC 2001
The Plant Journal
Volume 28, Issue 2, pages 181–190, October 2001
How to Cite
Izhaki, A., Swain, S. M., Tseng, T.-s., Borochov, A., Olszewski, N. E. and Weiss, D. (2001), The role of SPY and its TPR domain in the regulation of gibberellin action throughout the life cycle of Petunia hybrida plants. The Plant Journal, 28: 181–190. doi: 10.1046/j.1365-313X.2001.01144.x
- Issue published online: 23 DEC 2001
- Article first published online: 23 DEC 2001
- Received 16 March 2001; revised 19 July 2001; accepted 19 July 2001.
- Petunia hybrida;
- seed germination;
- signal transduction;
SPY acts as a negative regulator of gibberellin (GA) action in Arabidopsis, but its mode of action and regulation are still unknown. SPY over-expression in transgenic petunia plants affected various GA-regulated processes, including seed germination, shoot elongation, flower initiation, flower development and the expression of a GA-induced gene, GIP. A similar phenotype was obtained when wild-type petunia plants were treated with the GA-biosynthesis inhibitor, paclobutrazol. The N-terminus of SPY contains tetratricopeptide repeats (TPR). TPR motifs participate in protein–protein interactions, suggesting that SPY is part of a multiprotein complex. To test this hypothesis, we over-expressed the SPY's TPR region without the catalytic domain in transgenic petunia and generated a dominant-negative SPY mutant. The transgenic seeds were able to germinate on paclobutrazol, suggesting an enhanced GA signal. We cloned the petunia SPY homologue, PhSPY, and showed that its mRNA level is not affected by GA or ABA. The results of this study support the role of SPY as a negative regulator of GA action, suggest that the TPR domain is required for the interaction with other proteins to form an active complex and indicate that different plants use similar mechanisms to transduce the GA signal.