Abstract

Weeds are the most serious biological constraints in agriculture causing crop production losses of worth several billion dollars world wide annually and also spending billions of dollars to remove or control weeds in agriculture. Manual weeding over large areas is difficult in terms of availability of labor and the associated monitory cost. Moreover, manual weeding is very time consuming and slow processes. In such a scenario chemical weed control is extremely important. Such technologies were not developed in India and the not access to Indian Farmers. Our group developed rice plants simultaneously resistant to more than one herbicide with different mode of action to control the weeds without causing any injury to rice crop. We have selected two broad-spectrum non-selective systemic herbicides sulfonylurea for pre-emergent application and glyphosate for post-emergent application. Sulfonylurea is a very strong inhibitor of Acetolactate synthase, an important plant enzyme involved in branched chain amino acids Valine, Leucine and Isoleucine. Similarly glyphosate is a strong inhibitor of EPSP synthase another important plant enzyme involved in aromatic amino acids Phenylalanine, Tryptophan and Tyrosine. We followed herbicide target site modification strategy to develop herbicide tolerance in rice without introducing any foreign gene. We have introduced selective amino acid substituting mutations in EPSPS and ALS that interfere with ability of the herbicide to interact with these important plant enzymes. The mutated EPSPS and ALS retain their normal functioning of the enzyme in the presence of the herbicide. The transgenic rice plants that constitutively over expressing mutated rice EPSP synthase and Acetolactate synthase did not showed any growth retardation even at 6 fold higher herbicide that is recommended for weed control in agriculture. We also developed phosphite based pre- and post-emergent weed-controlling technology with several added advantages. We have constitutively expressed codon optimized synthetic phosphate dehydrogenase encoding gene in transgenic rice that able to metabolize PO3 as a P fertilizer but not the non-transgenic control rice. Our results clearly shows that PO3 can act as fertilizer for transgenic crop and simultaneously act as herbicide on the weeds.