From QTL to variety-harnessing the benefits of QTLs for drought, flood and salt tolerance in mega rice varieties of India through a multi-institutional network

Rice is a staple cereal of India cultivated in about 43.5Mha area but with relatively low average productivity. Abiotic factors like drought, flood and salinity affect rice production adversely in more than 50% of this area. Breeding rice varieties with inbuilt tolerance to these stresses offers an economically viable and sustainable option to improve rice productivity. Availability of high quality reference genome sequence of rice, knowledge of exact position of genes/QTLs governing tolerance to abiotic stresses and availability of DNA markers linked to these traits has opened up opportunities for breeders to transfer the favorable alleles into widely grown rice varieties through marker-assisted backcross breeding (MABB). A large multi-institutional project, "From QTL to variety: marker-assisted breeding of abiotic stress tolerant rice varieties with major QTLs for drought, submergence and salt tolerance" was initiated in 2010 with funding support from Department of Biotechnology, Government of India, in collaboration with International Rice Research Institute, Philippines. The main focus of this project is to improve rice productivity in the fragile ecosystems of eastern, northeastern and southern part of the country, which bear the brunt of one or the other abiotic stresses frequently. Seven consistent QTLs for grain yield under drought, namely, qDTY1.1, qDTY2.1, qDTY2.2, qDTY3.1, qDTY3.2, qDTY9.1 and qDTY12.1 are being transferred into submergence tolerant versions of three high yielding mega rice varieties, Swarna-Sub1, Samba Mahsuri-Sub1 and IR 64-Sub1. To address the problem of complete submergence due to flash floods in the major river basins, the Sub1 gene is being transferred into ten highly popular locally adapted rice varieties namely, ADT 39, ADT 46, Bahadur, HUR 105, MTU 1075, Pooja, Pratikshya, Rajendra Mahsuri, Ranjit, and Sarjoo 52. Further, to address the problem of soil salinity, Saltol, a major QTL for salt tolerance is being transferred into seven popular locally adapted rice varieties, namely, ADT 45, CR 1009, Gayatri, MTU 1010, PR 114, Pusa 44 and Sarjoo 52. Genotypic background selection is being done after BC2F2 stage using an in-house designed 50K SNP chip on a set of twenty lines for each combination, identified with phenotypic similarity in the field to the recipient parent. Near-isogenic lines with more than 90% similarity to the recipient parent are now in advanced generation field trials. These climate smart varieties are expected to improve rice productivity in the adverse ecologies and contribute to the farmer's livelihood.

Expression of hepatitis B surface antigen in tobacco cell suspension cultures

Hepatitis B virus ' s ' gene coding for surface antigen was cloned into plant transformation vectors pHER100 and pHBs100 with and without endoplasmic reticulum retention signal, respectively. Transformed tobacco cell lines were analyzed for the integration of the transgene by PCR and Southern blot hybridization. Expression levels as determined by ELISA showed maximum expression levels of 2 microg HBsAg gm(-1) fresh weight and 10 ng mL(-1) of spent medium in pHER100 transformed cells. Western blot analysis confirmed the presence of 24 kDa band specific to HBsAg in the transformed cells. HBsAg was expressed both as intracellular and secreted forms in pHER100 transformed cells. The buoyant density in CsCl of HBsAg derived from pHBs100 transformed tobacco cells was determined and found to be 1.095 g mL(-1). HBsAg obtained from transformed tobacco cells is similar to the human serum derived one in buoyant density properties. This is the first report on the secretion of HBsAg particles by plant cells into the cell culture medium.