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Transgenic crops targeting ion homeostasis machinery: Bangladesh perspective for adaptation to climate Change to ensure food security

Anamika Datta
Plant Biotechnology Lab, Biotechnology Program, Dept. of Mathematics and Natural Sciences, BRAC University, 66, Mahakhali C/A. Dhaka-1212, Bangladesh

Mashiat Nawar Chowdhury
Plant Biotechnology Lab, Biotechnology Program, Dept. of Mathematics and Natural Sciences, BRAC University, 66, Mahakhali C/A. Dhaka-1212, Bangladesh

Aparna Islam
Plant Biotechnology Lab, Biotechnology Program, Dept. of Mathematics and Natural Sciences, BRAC University, 66, Mahakhali C/A. Dhaka-1212, Bangladesh

Abstract/ Executive Summary:

Salinity stress is one of the major adversarial impacts of climate change that limits crop productivity worldwide, especially in developing countries. To overcome this situation it is necessary to understand the cellular basis of salt stress tolerance mechanisms. Various genes involved in ion exclusion, osmotic tolerance, Reactive Oxygen Species (ROS) scavenging and other regulation mechanisms influence salinity tolerance in crops. Function of these candidate genes/sequences may vary in different plants and within different tissues. For the last two decades, in Bangladesh several approaches have been taken to develop transgenic rice, the staple crop. Work is in progress to monitor stable incorporation of these transgenes. Further evaluation is needed to check their adaptation/resistance in natural environments. Good performance in field conditions will lead to acceptance of these varieties for commercial productions in order to ensure food security.

Keywords: Salinity, Salt tolerance, SOS pathway, Ion homeostasis, Transcription factor, Climate change, Agriculture

Location: All over Bangladesh

Start Date:

End Date:

Program Area: Food Safety and Security

Non-commodity: Adoption and mitigation technology

Objectives:

To determine the Bangladesh Perspective for Adaptation to Climate Change to Ensure Food Security

Methodology:

Bangladesh is the 7th most populated country of the world with current estimates of 160 million people. As rice is the staple food several attempts has been made for its improvement. Several attempts have been made to transfer the gene(s) described above into crop plants in order to improve tolerance. i. Targeting ion homeostasis machinery through vacuolar Na+/H+ antiporter genes (NHX): Binnatoa rice was transformed to improve salt tolerance by targeting ion homeostasis machinery by over-expression of OsNHX1 under the constitutive promoter Actin1D and CaMV35S. Degree of salt tolerance and overall performance of the two transgenic rice bearing Actin1D and CaMV35S promoters displayed no significant difference, suggesting similitude of role in gene regulation of the two constitutive promoters (Islam et al. 2009). ii. Targeting salt overly sensitive signaling pathway: In a study, the coding sequence of SOS1 gene (3447 bp) was cloned and transformed into farmer popular rice variety BRRI dhan28. The SOS1 gene encodes a plasma membrane Na+/H+ antiporter that play an important role in germination and growth in saline environments. This study showed an improved salinity tolerance level of 150 to 200 mM in the high yielding but salt sensitive BRRI dhan28 (Yasmin et al. 2015). iii. Targeting transcription factor machinery: To improve salt tolerance in rice by targeting transcription factor machinery, the SNAC1 gene (from the salt tolerant rice landrace Pokkali) was cloned and transformed into a salt sensitive rice variety Binnatoa (Abdullah-Al-Emran et al. 2010) and BRRI dhan55 using the in planta method. The transgenic lines exhibited better tolerance compared to the non-transgenic plants at 120 mM salt (Parvin et al. 2015). Targeting replication machinery: To improve the salinity tolerance of rice a DEAD?box helicase (PDH45) gene from pea was introduced into Binnatoa through Agrobacterium' mediated transformation. Higher chlorophyll content, decreased root length and higher leaf K⁺/Na⁺ ratio was found in transgenic plants compared to wild type plants under salt stress, which indicated induced ion homeostasis. Moreover, PDH45 expressing transgenic rice plants showed better fertility at the reproductive stage and produced much higher grain yield compared to WT plants under continuous salt stress. ii. Pyramiding of antioxidant genes: To develop transgenic salt tolerant rice by targeting antioxidant machinery, Singla-Pareek and her colleagues utilized two genes that encodes for Glyoxalase I (isolated from a Brassica juncea) and Glyoxalase II (isolated from Oryza sativa L.cv IRBB10) (Singla-Pareek et al. 2008). These genes are involved in salt tolerance mechanism through glutathione?based detoxification of methylglyoxal in plant. The transgenic plants showed higher constitutive activity of glyoxalase II that increased further upon salt stress, reflecting the upregulation of endogenous glyoxalase II. The transgenic rice showed higher tolerance to toxic concentrations of methylglyoxal (MG) and NaCl. Prodhan et al. (2010) reported successful introduction of katE gene in three rice cultivars, Nipponbare, Kasalath and BR?5 successfully. Introduction of katE gene significantly improved the salt tolerance of the transgenic indica lines which could mature and set seed under stress at 100mM salt. Particularly, these transgenic plants could survive for one month in 150 mM and for 20 days in 200 and 250 mM NaCl (Prodhan et al. 2010). iii. Targeting different transcript sizes of anti-porter genes: The rice OsNHX1 antiporter gene produces three different transcripts where transcript 1 and 2 produce proteins of equal size, while transcript 3 produces a truncated protein at the C terminus region. However, the 5- Un-Translated region (UTR) is variable in all three transcripts of the OsNHX1 gene (196, 325, and 186 bp in transcript 1, 2, and 3, respectively), (LOC_Os07g47100, gramene). This is in contrast to Arabidopsis (a model plant and not a crop species like rice) which has only a single transcript. The properties of a transcript are controlled by some features of their UTRs as the UTR of a gene has important biological roles which can influence the half?life, intracellular localization, and differential translational efficiency of the corresponding mRNA, particularly for regulatory genes responsive to stress. Over?expression of vacuolar Na+/H+ antiporter from the CDS and 5- UTR (1.9 kb) and complete cDNA (2.3 kb) that a higher level of reproductive level salt tolerance was reported for the 2.3 kb construct compared to the moderate level of stress obtained from the 1.9 kb construct. The result of the experiment showed increased expression of the OsNHX1 gene under 100 mM salt stress (NaCl) only in case of the 2.3 kb transgenic line along with higher K+ content (Biswas et al. 2016). iv. Combining genes to improve salt tolerance: Integration of multiple copies of transgene at the same locus has reported to be associated with the instability of transgene expression in plants. However, insertion of two genes is also reported to be acceptable. In this study, the double copies of the transgene actually showed considerably better salinity tolerance compared to the non?transformed wild type BRRI dhan28 (Biswas et al. 2016).

Source of Information: Plant Tissue Cult. & Biotech. 27(2): 241?256, 2017 (December)

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Achievement/Findings:

One of the alarming issues of the present day and also for the forthcoming future is ensuring food security. One approach to address these challenges, has been to include saline soil as arable area. However, we need successful development of more transgenic salt?tolerant crops which will effectively survive in saline stresses field conditions. Moreover, we need functional greenhouses for contained trials and field facilities to test them under confined conditions. The regulatory system also needs to be made free of bureaucratic delays. Therefore, there needs to be more investment in research training as well as infrastructure. The promise of genome?editing technologies like Crispr-Cas9, which is not only technically friendly but also may need less regulatory oversight, should be adopted with urgent research funding.

Knowledge Management: Journal