STUDY OF THE STRUCTURE AND FUNCTION OF HETEROTRIMERIC G PROTEINS IN PLANTS

含有水稻异源三聚体G蛋白α亚基反义cDNA的转基因水稻产生很少或没有亚基的mRNA，并表现出异常的形态，包括矮秆性状和小种子的设置。在正常水稻中，α亚基的mRNA在与矮秆转化体异常密切相关的节间和小花中大量表达。利用限制性片段长度多态性（RFLP）技术将该基因定位在水稻第5染色体上。该位置与水稻矮秆突变体Daikoku dwarf（d1）的基因座紧密连锁，该突变体已知表现出与通过反义技术抑制α亚基的内源mRNA的转化体相似的异常表型。含有异源三聚体G蛋白α亚基基因（RGA 1）的启动子区和GUS基因的嵌合体基因，将其导入正常栽培品种，并将第三代种子（T3种子）用于进一步分析。萌发期，在糊粉层、盾叶上皮和叶鞘中检测到GUS活性。在发育期，主要分布在节间。在抽穗前，GUS活性定位于外稃和内稃。抽穗后，在花粉中检测到。水稻矮秆突变体d1在叶鞘、节间、外稃和内稃中的α亚基的表达与表型异常有关。与野生型相比，赤霉素对d1糊粉细胞α-淀粉酶活性的诱导作用大大降低。这一结果表明异源三聚体G蛋白与赤霉素信号转导有关。

Transgenic rice containing an antisense cDNA for the α subunit of rice heterotrimeric G protein produced little or no mRNA for the subunit and exhibited abnormal morphology including dwarf traits and the setting of small seeds. In normal rice, the mRNA for the α subunit was abundant in the internodes and florets, the tissues closely related to abnormality in the dwarf transformants. The position of the α-subunit gene was mapped on rice chromosome 5 by mapping with the restriction fragment length polymorphism. The position was closely linked to the locus of a rice dwarf mutant, Daikoku dwarf (d1), which is known to exhibit abnormal phenotypes similar to those of the transformants that suppressed the endogenous mRNA for the α subunit by antisense technology.The chimera gene containing the promoter region of the gene of the α subunit of a heterotrimeric G protein (RGA1) and GUS gene, was introduced to the normal cultivar and the seeds at third generation (T3 seeds) were used for further analysis. In germination stage, the GUS activity was detected in aleurone layer, scutellar epithelium and leaf sheath. In the developing stage, it was largely observed in the internodes. Before heading, GUS activity was localized in the lemma and palea. After heading, it was detected in pollen. The expression of the α subunit in leaf sheath, internode, lemma and palea is accountable for explanation of abnormal phenotypes in Daikoku d1.Rice dwarf mutant, d1, is defective in the α subunit of the heterotrimeric G protein. Compared with the wild type, gibberellin induction of α-amylase activity in aleurone cells of d1 was greatly reduced. This result shows that the heterotrimeric G protein concern the gibberellin signal transduction.