136HORIZONTAL GENE TRANSFER IN PLANTSThe transfer of genetic material from parent to offspring via reproduction is called vertical gene transfer. Horizontal gene transfer (HGT) is also referred as lateral gene transfer (LGT), relates to the process in which transfer of genetic material between cells or genomes belonging to unrelated species, occur by processes other than usual reproduction. Since HGT is an asexual process, it is not restricted by species boundaries and organisms as diverse as prokaryote/eukaryote can engage in the horizontal exchange of genetic information. In many prokaryotes, HGT has contributed 10 to 20 percent of the genes. It has often critically influenced prokaryotic evolution, leading to acquisition or modification of important traits such as antibiotic resistance, virulence, photosynthesis and nitrogen fixation. Though HGT occurs much less frequently in eukaryotes it is not merely a rare evolutionary accident or curiosity, but rather a highly significant process in eukaryotic genome evolution as evidenced in chloroplast genome of plants. Among the eukaryotes, unicellular ones generally experience the HGT.In plants, the first reported eukaryote to eukaryote nuclear HGT is related to transposons.Another case of plant HGT was detected in the parasitic plant Strigahermonthica that infests monocots such as sorghum and rice. During pathogenesis, Agrobacterium transforms its host with several plasmid-encoded genes, with HGT as a natural consequence. Other examples include the acquisition of aquaglyceroporins from a Eubacterium 1200 million years ago and glutathione biosynthesis genes from a Proteobacterium. Plant mitochondrial genomes experience the most frequent and evolutionarily widespread horizontal transfer of genes acquired from other eukaryotes. Horizontal transfer of genes among tobacco species has been demonstrated through in vitro graft experiments. The mechanism of HGT is not well understood. However, it can increase genetic diversity and promote the novel adaptations in living organism.amylarapu001@gmail.comResearch492014HGT, Striga hermonthica,Agrobacterium,EubacteriumM. Amaranatha Reddy,T. Rajeswar reddy,T.L. DheemanthPh.D Scholar, Dept. of Plant Breeding and Genetics, COH, KAU, Vellanikkara, Thrissur, Kerala, India.,Ph.D Scholar, Dept. of Plant Pathology, COH, KAU, Vellanikkara, Thrissur, Kerala, India.,M.Sc. (Ag), Dept. of Plant Biotechnology, COH, KAU, Vellanikkara, Thrissur, Kerala, India