Genetic Engineering Approaches For Tolerance Against Abiotic Stress
Authors: Waghmare S. T^*., Belge S. A., Yeole P.T., Kharade S. S., Chavan N. S.
Sandeshwaghmare174@gmail.com


Article summary: Abiotic stress is the negative impact of non-living factors on living organism in a specific environment. It is naturally occurring and often intangible factors.Abiotic stresses are the main factors that limit crop productivity. Drought, salinity and heavy metals stresses caused yield losses annually to a greater extent. Transgenic development is another straight forward technology to improve crop yield in abiotic stress affected land. The development of tolerant crops by genetic engineering, on the other hand, requires the identification of key genetic determinants underlying stress tolerance in plants and introducing these genes into crops. The advent of plant transformation may have placed within the grasp of the possibility of engineering greater abiotic stress tolerance in plants.

Introduction:

Plant Genetic Engineering is the transfer of genes from one organisms or even synthetic DNA sequences into the genome of another organism. This capability can be and has been exploited to tailor plant genomics to suit various human needs. One of the best example is the production of transgenic plants which is tolerance to biotic and abiotic stress. A stress is defined as factors of environment interfering the complete expression of the genotypic potential of an organism. It may be biotic stress and abiotic stress. Abiotic stress is the negative impact of non-living factors on living organism in a specific environment. It is naturally occurring and often intangible factors.Abiotic stresses are the main factors that limit crop productivity. Drought, salinity and heavy metals stresses caused yield losses annually to a greater extent. Abiotic stress reducing average yields of crops by up to 50 per cent and annually about 42 per cent of the crop productivity is lost owing to various abiotic stress factors. Transgenic development is another straight forward technology to improve crop yield in abiotic stress affected land. The development of tolerant crops by genetic engineering, on the other hand, requires the identification of key genetic determinants underlying stress tolerance in plants and introducing these genes into crops. The advent of plant transformation may have placed within the grasp of the possibility of engineering greater abiotic stress tolerance in plants.

Genetic engineering for Drought Tolerance

Drought is a period or condition of unusually dry weather within a geographic area where there is a lack of precipitation. Drought is governed by various factors, the most prominent being extremes in temperature, photon irradiance and paucity of water. The characteristics features of drought stress are low water potential due to high solute concentration. Low water supply causes soil mineral toxicities and can make a plant more susceptible to damage from high irradiance.

• Mechanism of drought tolerance

1) DROUGHT ESCAPE: It is defined as the ability of a plant to complete its life cycle before supply of water in soil is depleted and form dormant seeds before the onset of dry season. These plants are known as drought escapers since they escape drought by rapid development.

2) DROUGHT AVOIDANCE: It is the ability of plants to maintain relatively high tissue- water potential despite a shortage of soil-moisture. Drought avoidance is performed by maintenance of turgor through roots grow deeper in the soil, stomatal control of transpiration and by reduction of water loss through reduced epidermal i.e. reduced surface by smaller and thicker leaves.

3) DROUGHT TOLERANCE: It is the ability to withstand water-deficit with low tissue water potential. Drought tolerance is the maintenance of turgor through osmotic adjustment (a process which induces solute accumulation in cell), increase in elasticity in the cell and decrease in cell size.

• Barley gene in rice for drought tolerance:

Gene HVA1 encodes for a group of three LEA proteins which get accumulated in vegetative organs during drought condition. This gene was isolated from barley and introduced into the rice. The gene was inserted in the pBY520 vector and introduced into the rice by gene gun. The expression of the HVA1 is controlled by the rice actin gene. Transgenic rice plants showed significantly increased tolerance to water deficit and salinity. Transformed Plants maintained higher growth rates than non-transformed control plants under stress conditions. The increased tolerance was also reflected by delayed development of damage symptoms caused by stress and by improved recovery upon the removal of stress conditions. The extent of increased stress tolerance correlated with the presesne of the HVAl protein accumulated in the transgenic rice plants

Genetic engineering for Salt / Salinity Tolerance

Salt tolerance is an important trait that requires overcoming salinity induced reduction in plant productivity. The genetic response ofplants to abiotic stresses is complex involving simultaneous expression of a number of genes. Plant genetic engineering techniques could be effectively utilized to exploit some of the untapped potentials to increase the harvestable crop yield. It involves specific genemanipulation either through over expression or silencing of alien/native genes. A number of genes induced in response to salinity have been identified from a range of organisms adapted to stressful environment If a salt tolerant gene is identified which can lead to betterment of the crops, it is possible to transfer that progress in transgenic research for inclusion salinity stress tolerance.

• Yeast gene in Tomato for salinity Tolerance

Saccharomyces genes HAL1 and HAL3, which are involved in the regulation of K1 and Na1 transport respectively. Introduction of the yeast HAL1 gene (using a modified plasmid with enhancer elements) in tomato (Lycopersicon esculentum cv P-73). Over expression of HAL 1 gene in yeast confers a high salt tolerance level by reducing K loss and decreasing intracellular Na from the cells upon salt stress. HAL 1 ability to maintain K uptake in the presence of external Na, as shown by the transgenic families (especially TG3), is noteworthy. This ability has been related to salt tolerance in tomato. The salt tolerance levels of transgenic tomato plants assayed in this work were higher than that previously observed in melon. This could be due to genetically engineered plasmid used in this work, which had a duplicated 35S promoter.

Genetic Engineering for Heat Tolerance

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

Introduced Arabidopsis thaliana hsp101 (Athsp101) cDNA into the Pusa basmati 1 cultivar of rice (Oryza sativa L.) by Agrobacterium mediated transformation. Diagrammatic representation of pUH-Athsp101 construct employed for rice transformation is given below



Comparison of survival of transgenic lines after exposure to different levels of high-temperature stress with the untransformed control plants were performed and the result shows that

• The transgenic rice lines showed significantly better growth performance in the recovery phase following the stress
• The results showed that all transgenic rice plants survived in the high-temperature range of 45–50 ◦C exhibiting vigorous growth during the subsequent recovery at 28 ◦C, whereas most of the untransformed plants succumbed.
• These tests revealed that AtHsp101 imparts basal high temperature tolerance possibly by acting in the post-stress recovery period.
  
  Genetic Engineering for Cold Tolerance
  
  Modification of Enzyme

• The chilling sensitivity of plants is closely correlated with the degree of unsaturation of fatty acids.Plants with high proportion of cis unsaturated fatty acids such as Squash and Arabidopsis are resistant to chilling. The chloroplast enzyme glycerol-3-phosphate acetyl transferase seems to be important for determining phosphatidyl glycerol fatty acids unsaturation

Here the FA unsaturation has been modified by transferring the said enzyme DNA from quash and Arabidopsis. cDNA for enzyme from Squash and Arabidopsis with CaMV-35S constitute promoter in pBI21 and pARA respectively was introduced to Tobacco through Agrobacterium mediated gene transfer and the result shows that Plants with pBI-121 show little resistance andPlants with pARA resistant to chilling than wild type.

References:

1. Roy, B., Noren, S.K.,. Mandal, A. B., and Basu, A.K. (2011). Genetic Engineering for Abiotic Stress Tolerance in Agricultural Crops. Biotechnology, 10: 12
2. Apse, M.P. and Blumwald.E (2002). Engineering salt tolerance in plants. Current Opinion in Biotechnology. 13:146â€"150
3. Bhatnagar, P., Mathur, V. V., and Sharma, K.K.(2008). Transgenic approaches for abiotic stress tolerance in plants: retrospect and prospects. Plant Cell Rep (2008) 27:411â€"424
4. Hussain, S.S., Raza, H., Afzal, M., and Kayani, M.A. (2012) Transgenic plants for abiotic stress tolerance. Current status, Archives of Agronomy and Soil Science, 58:7, 693-721


About Author / Additional Info:
I am currently working as Assistant professor at K.K. Wagh College of Agricultural Biotechnology, Nashik