作者:Yuri KANNO、Kazuko OTOMO、Hiromichi KENMOKU、Wataru MITSUHASHI、Hisakazu YAMANE、Hideaki OIKAWA、Hiroaki TOSHIMA、Makoto MATSUOKA、Takeshi SASSA、Tomonobu TOYOMASU
DOI:10.1271/bbb.60044
日期:2006.7.23
We have previously isolated and characterized the rice (Oryza sativa) cDNAs, OsCyc1/OsCPS4, OsCyc2/OsCPS2, OsKS4, OsDTC1/OsKS7, OsDTC2/OsKS8 and OsKS10, which encode cyclases that are responsible for diterpene phytoalexin biosynthesis. Among the other members of this gene family, OsCPS1 and OsKS1 have been suggested as being responsible for gibberellin biosynthesis, OsKSL11 has recently been shown to encode stemodene synthase, and the functions of the three other diterpene cyclase genes in the rice genome, OsKS3, OsKS5 and OsKS6, have not yet been determined. In this study, we show that recombinant OsKS5 and OsKS6 expressed in E. coli converted ent-copalyl diphosphate into ent-pimara-8(14),15-diene and ent-kaur-15-ene, respectively. Neither product is a hydrocarbon precursor required in the biosynthesis of either gibberellins or phytoalexins. OsKS3 may be a pseudogene from which the translated product is a truncated enzyme. These results suggest that the diterpene cyclase genes responsible for gibberellin and phytoalexin biosynthesis are not functionally redundant.
我们之前分离并鉴定了水稻(Oryza sativa)cDNA OsCyc1/OsCPS4、OsCyc2/OsCPS2、OsKS4、OsDTC1/OsKS7、OsDTC2/OsKS8和OsKS10,这些基因编码的环化酶负责二萜类植物抗毒素的生物合成。在该基因家族的其它成员中,OsCPS1和OsKS1被认为负责赤霉素的生物合成,OsKSL11最近被证明编码茎酮合成酶,而水稻基因组中另外三个二萜类环化酶基因OsKS3、OsKS5和OsKS6的功能尚未确定。在这项研究中,我们发现重组的OsKS5和OsKS6在大肠杆菌中表达,分别将ent-copalyl二磷酸转化为ent-pimara-8(14),15-二烯和ent-kaur-15-烯。这两种产物都不是赤霉素或植物抗毒素生物合成所需的烃类前体。OsKS3可能是一个假基因,其翻译产物是一种截短的酶。这些结果表明,负责赤霉素和植物抗毒素生物合成的二萜类环化酶基因在功能上不是多余的。