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

已知Ri质粒T-DNA上的rol基因是引起毛状根病的主要因素。为了阐明rolC基因的生理功能，将rolC基因的结构基因与CaMV 35 S启动子连接，构建了一个嵌合基因，并将其导入颠茄中。转基因颠茄表现出矮化和早花的表型。在相当于P1生物防护水平的温室中培养转基因植株的自花授粉后代，并在第1和第2代中检查形态和生理特性。后代可分为3种类型。类型1表现出与未转化植株相似的性状，类型2表现出与转化植株相同的矮化和早花现象，类型3表现出生长抑制和不分化花。类型1、2、3的分离比分别约为1：2：1。认为导入颠茄的嵌合rolC基因作为显性基因发挥功能，rolC基因的过表达抑制了rolC纯合植物的生长。这些结果表明，rolC基因的表达的适当控制是必需的，在其应用于植物育种。另一方面，内源激素的定性和定量分析进行了使用上述类型1和2颠茄。类型2茎、叶中脱落酸、细胞分裂素和赤霉素含量略有增加，而根中含量无明显差异。当用各种植物生长调节剂处理1型和2型植物时，植物不显示早期开花，这是在用rolC基因转化的植物中观察到的特征性特征。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的结果不一致。rolC基因在生理功能上的另一种可能性值得考虑。

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.