Advances in plant transformation technology 1. optimal transgene integration and its expression towards safer GM crops in the Indian context

For agriculture purposes, transgenic Genetically Modified (GM) crops are produced in two steps, a) production of the Primary Transformant by transferring the gene of interest (goi) from any species/source to a suitable plant host by recombinant DNA technology/Genetic Engineering (GE). In the second step b) the goi is further transferred from the primary transformant to a suitable high yielding crop line by plant breeding protocol. Despite rigorous steps followed in GM crop production, there is evidence of some uneven performance of Bt cotton and gradual shift from cotton to soybean cropping in our area, in Western MP, India. There is therefore, need for investigations to explore the mechanisms of transgene transfer. Recombinant DNA scientists, the genetic engineers, globally, have been and are actively engaged in this direction. The aim of this review is to highlight some of these untiring efforts. This review covers mainly researches on, Agrobacterium-mediated gene transfer. The focus is on better understanding of Agrobacterium-plant host interactions to overcome barriers of recalcitrant crop species, innovations for site-specific targeted single copy transgene integration and avoidance of transgene silencing for stable expression. Certain milestone advances in direct delivery protocols have also been discussed.