Poster: Intracellular Signaling

Abs # 823: A role of heterotrimeric G protein in gibberellin signaling in rice plant

Presenter:	Fujisawa, Yukiko , fujisawa@fpu.ac.jp
Authors	Fujisawa, Yukiko  (A)   Kato, Chiyuki  (A)   Hiraoka, Haruko  (A)   Ito, Kimiko  (B)   Mitsui, Toshiki  (B)   Kato, Hisaharu  (A)   Iwasaki, Yukimoto  (A)
Affiliations:	(A): Fukui Prefectural University (B): Niigata University

Plant heterotrimeric G protein are considered to transmit external signals to effectors. The molecular mechanisms in the signal transduction pathways, however, have not well been studied. To make the signaling pathways including plant heterotrimeric G proteins clear, we have analyzed rice transformants expressing a constitutively active a subunit of the rice G proteins. In this work, a glutamine at the amino acid position of 223 in the rice a subunit (RGA1) was changed to a leucine by an in vitro mutagenesis method (the resultant clone was named RGA1QL). The RGA1QL protein synthesized E. coli had GTP-binding activity but no GTPase activity, including that it is in a constitutively active form. We introduced RGA1QL cDNA to d1 which was a deficient mutant in the a-subunit gene for the rice G proteins to obtain the transformants (d1QL). The phenotypes of d1QL were wild-type-like and the length of seeds of d1QL was slightly longer than that of wild type rice. Without gibberellin, the a-amylase activity was detected in embryo-less half seeds of d1QL but not in those of wild type rice. The result indicates that the heterotrimeric G proteins function as a positive regulator in gibberellin signaling in rice.