Over-expression of the bacterial nhaA gene in rice enhances salt and drought tolerance

The Escherichia coli nhaA gene encodes a Na+/H+ antiporter, which plays a critical role in ion homeostasis. We transferred a bacterial nhaA gene into rice (Oryza sativa L. ssp. japonica) and detected high expression in the transgenic rice. The germination rate, growth, and average yield per plant of the transgenic lines were better than those of control lines under salt or drought stress. Moreover, the sodium and proline content of the transgenic lines under salt or drought stress was also higher than in control lines, implying that nhaA over-expression enhances osmoregulation by activating the biosynthesis of proline. Tolerance to both salt and drought was compared between transgenic rice over-expressing nhaA and that over-expressing Arabidopsis δ-OAT encoding ornithine-8-aminotransferase. The transgenic plants with nhaA grew better than those with δ-OAT at high salinity, while the opposite was true for drought stress.

Source: Plant science (2005) vol. 168, p. 297-302

Heat-tolerant basmati rice engineered by over-expression of hsp101

Rice is sensitive to high-temperature stress at almost all the stages of its growth and development. Considering the crucial role of heat shock protein 101 (Hsp 101) in imparting thermotolerance to cells, we introduced Arabidopsis thaliana hsp101 (Athsp101) cDNA into the Pusa basmati 1 cultivar of rice (Oryza sativa L.) by Agrobacterium-mediated transformation. Stable integration and expression of the transgene into the rice genome was demonstrated by Southern, northern and western blot analyses. There appeared no adverse effect of over-expression of the transgene on overall growth and development of transformants. The genetic analysis of tested T1 lines showed that the transgene segregated in a Mendelian fashion. We compared the survival of T2 transgenic lines after exposure to different levels of high-temperature stress with the untransformed control plants. The transgenic rice lines showed significantly better growth performance in the recovery phase following the stress. This thermotolerance advantage appeared to be solely due to over-expression of Hsp101 as neither the expression of low-molecular-weight heat shock proteins (HSPs) nor of other members of Clp family proteins was altered in the transgenic rice. The production of high temperature tolerant transgenic rice cultivars would provide a stability advantage under supra-optimal temperature regime thereby improving its overall performance.

Source: Plant Mol Biol. (2003) vol 51, p. 677-686

Transgenics of an elite indica rice variety Pusa Basmati 1 harbouring the codA gene are highly tolerant to salt stress

Transgenic lines of indica rice were generated by Agrobacterium-mediated transformation with the choline oxidase ( codA) gene from Arthrobacter globiformis. Choline oxidase catalyses conversion of choline to glycine betaine. Glycine betaine is known to provide tolerance against a variety of stresses. Molecular analyses of seven independent transgenic lines as performed by Southern, Northern and Western hybridization revealed integration and expression of the transgene as well as inheritance in the progeny plants. A good correlation was observed between levels of mRNA and protein accumulation, and a significant amount of choline oxidase product, i.e. glycine betaine, accumulated in R0 as well as R1 plants. Mendelian as well as non-Mendelian segregation patterns were obtained in the progeny plants. Challenge studies performed with R1 plants by exposure to salt stress (0.15 M NaCl) for 1 week, followed by a recovery period, revealed that in some cases more than 50% of the transgenic plants could survive salt stress and set seed whereas wild-type plants failed to recover.

Source: Theor Appl Genet. (2002) vol 106, p. 51-57