Reference "Rice dwarf mutant d1, which is defective in the alpha subunit of the heterotrimeric G protein, affects gibberellin signal transduction"

Reference ID

4654

Title

Rice dwarf mutant d1, which is defective in the alpha subunit of the heterotrimeric G protein, affects gibberellin signal transduction

Source

Proceedings of the National Academy of Sciences of the United States of America, 2000, vol. 97, pp. 11638-11643

Authors (7)

Ueguchi-Tanaka-M	Fujisawa-Y
Kobayashi-M	Ashikari-M
Iwasaki-Y	Kitano-H
Matsuoka-M

Abstract

Previously, we reported that the rice dwarf mutant, d1, is defective in the
alpha subunit of the heterotrimeric G protein (Galpha). In the present study,
gibberellin (GA) signaling in d1 and the role of the Galpha protein in the GA-
signaling pathway were investigated. Compared with the wild type, GA induction
of alpha-amylase activity in aleurone cells of d1 was greatly reduced. Relative
to the wild type, the GA(3)- treated aleurone layer of d1 had lower expression
of Ramy1A, which encodes alpha-amylase, and OsGAMYB, which encodes a GA-
inducible transcriptional factor, and no increase in expression of Ca(2 +)-
ATPase. However, in the presence of high GA concentrations, alpha- amylase
induction occurred even in d1. The GA sensitivity of second leaf sheath
elongation in d1 was similar to that of the wild type in terms of dose
responsiveness, but the response of internode elongation to GA was much lower in
d1. Furthermore, Os20ox expression was up- regulated, and the GA content was
elevated in the stunted internodes of d1. All these results suggest that d1
affects a part of the GA- signaling pathway, namely the induction of alpha-
amylase in the aleurone layer and internode elongation. In addition, a double
mutant between d1 and another GA-signaling mutant, slr, revealed that SLR is
epistatic to the D1, supporting that the Galpha protein is involved in GA
signaling. However, the data also provide evidence for the presence of an
alternative GA-signaling pathway that does not involve the Galpha protein. It is
proposed that GA signaling via the Galpha protein may be more sensitive than
that of the alternative pathway, as indicated by the low GA responsiveness of
this Galpha-independent pathway.