Ripening in papaya fruit is altered by ACC oxidase cosuppression

Papaya (Carica papaya) is a very important crop in many tropical countries but it is highly susceptible to parasitic diseases, physiological disorders, mechanical damage and fruit overripening. Here we report a study on ACC oxidase cosuppression and its effects on papaya fruit ripening. Papaya ACC oxidase was isolated using PCR and embriogenic cells transformed by biolistic using the CaMV 35S promoter to drive the expression of the PCR fragment in sense orientation. Fifty transgenic lines were recovered and 20 of those were grown under field conditions. Southern analysis showed incorporation of the transgene in different copy numbers in the papaya genome. Fruits were evaluated in terms of texture (firmness), colour development, respiration and ethylene production. A sharp reduction in ethylene and CO2 production was detected, whereas softening and colour development of the peel were also altered. Overall, transgenic fruits showed a delay in ripening rate. A reduction in mRNA level for ACC oxidase in transgenic fruit was clearly detectable by northern blot. More studies are necessary before this technology can be used to extend the shelf life of papaya fruit.     

转基因植物内源基因与外源基因共抑制问题研究进展

在植物基因工程研究中,有时外源转化基因和植物中同源的内源基因的表达均被抑制了,这种现象被称为共抑制。引起该现象的原因包括许多因素,有外源基因和与之同源的内源基因RNA的转录量,DNA的甲基化,T-DNA的结构形式,RNA依赖的RNA聚合酶,非正常RNA以及非等位配对等。其具体机制仍不清楚。最近的研究结果表明转基因植物对病毒的抗性在某些方面与共抑制有相似之处。两者都表现为外源转化基因转录水平很高而稳定RNA的水平很低。本文综述了这方面的最新研究进展。     

查尔酮合酶基因对转基因植物花色和育性的影响

查尔酮合酶 ( chalcone synthase,CHS)是花色素合成途径中的一个关键酶 ,它在植物中表达量的改变可能影响花的颜色。从矮牵牛 ( Petunia hybrida)特定发育阶段的花瓣的 c DNA中 ,克隆到查尔酮合酶基因 ,并正向插入到原核表达载体和含有花椰菜花叶病毒 Ca MV 35 S启动子的真核表达载体中 ,在原核中得到高效表达 ,并通过土壤农杆菌介导的方法转化矮牵牛。转基因植物的花色不但发生了明显的变异 ,其育性也受到了影响 ,不能产生正常花粉粒 ,成为雄性不育植株。 Northern杂交表明 ,转基因植物花瓣中 ,内源及外源查尔酮合酶基因转录均受到抑制