Analysis of flower induction by Ri rolC gene and its application to plant breeding

众所周知，Ri质粒T-DNA上的rol基因是毛状根病害的主要致病因子。为了阐明RolC基因的生理功能，构建了一个结构完整的RolC基因与CaMV35S启动子连接的嵌合基因，并将其导入颠茄。转基因颠茄表现出矮化和早花表型。转基因植株的自花授粉后代在相当于P1生物容限水平的温室中培养，并对第1代和第2代的形态和生理特性进行了观察。子代分为3种类型。类型1的植株与未转化的植株特征相似，类型2的植株与转化植株一样表现为矮化和早花，类型3的植株生长受抑且不分化花。类型1、类型2和类型3的分离比分别约为1：2：1。有研究认为，在颠茄中导入的RolC嵌合基因是一个显性基因，该基因的过度表达抑制了RolC纯合子植株的生长。这些结果表明，在植物育种应用中需要适当控制RolC基因的表达。另一方面，对上述类型1和2的颠茄进行了内源植物激素的定性和定量分析。类型2茎叶中脱落酸、细胞分裂素和赤霉素含量略有增加，而根中含量无明显变化。当用不同的植物生长调节剂处理类型1和类型2的植株时，植株没有表现出早花的特征，这是转RolC基因植株的一个特征。这些结果与以前报道的(RolC基因编码细胞分裂素葡萄糖苷酶)不一致。因此，我们需要考虑RolC基因生理功能的另一种可能性。

It is well known that the rol genes on T-DNA of Ri plasmids are a main factor for hairy root disease. To clarify physiological functions of rolC gene, a chimeric gene, of which the structural rolC gene was ligated with CaMV35S promoter, was constructed and introduced into belladonna. The transgenic belladonna showed dwarfism and early flowering phenotype. Self-pollinated progenies of the transgenic plants were cultivated in a greenhouse equivalent to P1 biological containment level and the morphological and physiological characteristics were examined in the 1st and 2nd generations. The progenies were divided into 3 types. Type 1 plants had similar characteristics as those of non-transformed one, type 2 showed dwarfism and early flowering as same as those in the transformed plants and type 3 showed suppression in the growth and did not differentiate flowers. The segregation ratio of type 1, 2 and 3 was about 1 : 2 : 1, respectively. It is thought that the chimeric rolC gene delivered into belladonna functions as a dominant gene and the growth of rolC homozygous plants was suppressed by over expression of the rolC gene. These results indicate that the appropriate control of the rolC gene expression is required in its application to plant breeding.On the other hand, qualitative and quantitative analyzes of endogenous phytohormones were carried out using type 1 and 2 belladonna described above. The contents of abscisic acid, cytokinin, and gibberellin in stems and leaves increased slightly in type 2, but no difference in the contents was observed in roots. When type 1 and 2 plants were treated with various plant growth regulators, the plants did not show early flowering which is a characteristic feature observed in plants transformed with rolC gene. These results did not coincide with the previously reported one (rolC gene encodes cytokinin glucosidase). It is required to consider another possibility on physiological function of rolC gene.