Ts. Tseng et al., Ectopic expression of the tetratricopeptide repeat domain of SPINDLY causes defects in gibberellin response, PLANT PHYSL, 126(3), 2001, pp. 1250-1258
The SPINDLY (SPY) protein of Arabidopsis is a negative regulator of gibbere
llin (GA) response. The SPY protein has 10 copies of the tetratricopeptide
repeat (TPR) at the N terminus. TPR motifs function as protein-protein inte
raction domains. Several spy alleles are affected only in the TPR region su
ggesting that protein-protein interactions mediated by this domain are impo
rtant for proper GA signaling. We have used a reverse genetics approach to
further investigate the role of the TFR domain. The TPR domain of SPY was o
verexpressed in wild-type, gai, and spy plants. Expression of the TPR domai
n alone is not sufficient to rescue spy mutants. Expression of the TPR doma
in in a wild-type background produces phenotypes similar to those caused by
loss-of-function spy mutants including resistance to GA biosynthesis inhib
itors, short hypocotyl length, and early flowering. The dwarfing of the flo
ral shoot internodes caused by the gai mutation was suppressed by expressio
n of the TRP domain. Expression of the TPR domain had no effect on the abun
dance of endogenous SPY mRNA. : The TPR domain was found to interact with S
PY both in vitro and in yeast two-hybrid assays. These data indicate that t
he TPR domain of SPY can participate in protein-protein interactions and th
at these interactions are important for the proper functioning of SPY.