Crop improvement through genetic engineering: development of transformation technologies and production of stress tolerant transgenic crops
With the increase of environmental degradation, the crop improvement of stress tolerance becomes more important. Little success, however, has been achieved through traditional breeding method because of the limited availability of germplasm and the complexity of the genetic control of stress tolerance traits. Genetic engineering allows gene transfer between unrelated species. It greatly widens the genetic resource and is a good alternative for the improvement of stress tolerance. The goal of this study is to produce stress-tolerant maize and soybean to adapt to environmental stresses. Genetic transformation is used as a tool to achieve the goal. Since transformation technologies in maize and soybean are not robust in the respects of transformation efficiency and the quality of resulted products, the study also was focused on the development and optimization of maize and soybean transformation technologies.;Two available soybean transformation protocols were explored. Factors affecting the transformation efficiency of Agrobacterium-mediated cotyledonary node protocol were studied and optimized. Efforts also were made to repeat the controversial transformation protocol-soybean pollen-tube pathway transformation protocol because of the great interest with the tissue-culture free feature of the protocol. The result indicated that soybean pollen-tube pathway transformation is not reproducible. This study established a new Agrobacterium-mediated maize transformation protocol using a standard binary vector system. The resulting transgenic maize plants then were evaluated. Results showed that transformants generated from this new method have better qualities compared with those obtained from particle bombardment transformation.;This study showed that the expression of a tobacco mitogen-activated protein kinase kinase kinase gene, Nicotiana protein kinase 1 (NPK1) gene improved the freezing and drought tolerance in maize. This is the first report that freezing and drought traits were achieved in major crop maize through genetic engineering approach. Transgenic maize was identified to have elevated levels of several stress related gene expression, including DREB1, EREBP, EREBR1, GST and small HSP, indicating that the active NPK1 has induced the oxidative signaling pathway as expected and, therefore, protected maize plants from stress damage. NPK1 transgenic soybean also was produced. However, no advantage in drought tolerance was detected in these transgenic soybeans.