OMICS Based Strategies for Efficient Accumulation of Silicon in Rice to Enhance Its Tolerance against Environmental Stresses  

Sajad Majeed Zargar1 , Muslima Nazir2 , Ganesh Kumar Agarwal3 , Randeep Rakwal4,5
1. School of Biotechnology, SKUAST-J, Chatha, Jammu, J&K-180009, India
2. Department of Botany, Jamia Hamdard University, New Delhi-110062, India
3. Research Laboratory for Biotechnology and Biochemistry (RLABB), Kathmandu, Nepal
4. Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba305-8572, Japan
5. Department of Anatomy I, Showa University School of Medicine, Tokyo 142-8555, Japan
Author    Correspondence author
Molecular Plant Breeding, 2011, Vol. 2, No. 14   doi: 10.5376/mpb.2011.02.0014
Received: 01 Jun., 2011    Accepted: 15 Jul., 2011    Published: 15 Aug., 2011
© 2011 BioPublisher Publishing Platform
This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Preferred citation for this article:

Zargar et al., 2011, OMICS Based Strategies for Efficient Accumulation of Silicon in Rice to Enhance Its Tolerance against Environmental Stresses, Molecular Plant Breeding Vol.2 No.14 (doi: 10.5376/mpb.2011.02.0014)

Abstract

Silicon (Si) is a micronutrient. Its amount has been found to vary from plant to plant. Si in rice has been shown to provide tolerance against various biotic and abiotic stresses, especially rice blast and drought. Although rice contains higher amount of Si compared to other crops but the concentration varies between different species. In our own study we observed variation in the Si content among various genotypes of rice. A positive correlation between Si content in various plant parts of aerobically grown rice and the yield traits was observed, indicating the role of Si in giving tolerance against water stress. The genes responsible for Si accumulation in rice are known. However, the proteins induced due to Si application are to be mined. Here we propose a strategy based on genomics (molecular breeding) and proteomics approaches for effective utilization/incorporation of Si in commonly cultivated rice varieties to enhance its tolerance to various stresses.

Keywords
Silicon; Rice; Drought; Biotic stress; Abiotic stress

Among the major elements on this planet, silicon (Si) is known to be only second in abundance to oxygen in the outermost solid layer (crust) of our earth (Bond and McAuliffe, 2003). Moreover, Si has been accepted as an useful element for plant growth and development, not for all but in some species that have been studied (Gascho, 2001).Silicon has lot of beneficial effects (Epstein, 2001). It enhances the growth and yield, gives resistance against lodging, and enhances photosynthesis, resistance against phytopathogens, and resistance to abiotic stress like salinity, drought and protection against temperature extremes. Our own study revealed that rice genotypes with higher Si content show better tolerance to water stress and a positive correlation between Si content and yield attributing traits in aerobically grown rice was observed (Zargar et al., 2010). Earlier it was believed that Si accumulation in the cell wall prevents the pathogen entry, however recent evidences suggest that Si stimulates the expression of disease resistance genes in dicotyledons (Fawe et al., 2001). Silicon is deposited in plant cells and tissues, where it is known to help relieve the stress caused due to lack of water by reducing transpiration, improving light capture via an erect leaf blade, enhancing resistance towards pathogens and pests,improving nutrient imbalances, etc (Marschner, 1995; Epstein, 1994; Ma et al., 2002). In rice, the applied Si helped to reduce cadmium accumulation in cytoplasm, vacuole and other cellular organelles (Nwugo et al., 2008). All this illustrates the potential of Si.

The importance of rice as a essential crop plant is beyond doubt. It can be said that rice is a universal food grain being eaten by many peoples in various cultures. The United Nations launched 2004 as the International Year of Rice with-"Rice is life"-that reveals the critical importance of rice as one of the most important cereals in our food chain on this planet. One major challenge for agriculture is to produce more food with less water. Rice is mainly grown in submerged conditions, but there is a need to develop strategies for growing rice under low moisture conditions (Bouman and Tuong, 2001). Looking at the present climatic changes, it is predicted that there will be frequent and severe droughts in the future.

OMICS based technologies are of great value for crop improvement. Genomics based approaches such as utilization of molecular markers has uncovered its potential for crop improvement. Ma et al., (2004) conducted bulked segregant analysis experiment using microsatellite and expressed sequence tag (EST)-based PCR markers for mapping Si transporter gene. The gene was mapped to chromosome 2, and the microsatellite marker RM5303 and EST-based PCR marker E60168 were shown to flank this gene

So taking into consideration the role of Si in enhancing tolerance to various biotic and abiotic stresses, importance of rice and the potential of OMICS based technologies we here propose the strategies that can be utilized for improvement of rice crop.

1 OMICS based strategy for exploring the potential of Si in rice crop improvement
Genomics and proteomics technologies are presently well utilized to mine novel genes and potential candidate proteins. Though genomics will cover large number of approaches, here we will focus on Molecular Marker Assisted Back Cross (MABC) approach for accumulation of higher Si in rice. In case of proteomics study we will discuss a strategy through which novel proteins can be identified and used as the candidates for manipulating various metabolic processes to enhance tolerance of rice to various stresses.

1.1 Molecular breeding for enhancing accumulation of Si in rice
Through molecular breeding, it is feasible to transfer higher Si accumulation trait in elite rice cultivars. As Si transporter gene has been mapped on chromosome 2 by EST and microsatellite marker (Ma et al., 2004) the molecular markers linked to lsi 1 are known (Ma et al.; 2006). Hence these markers can be utilized in screening the available rice germplasm to identify the parental sources. The cultivar with highest Si content can be used as a donor parent for transferring the trait in an elite variety through backcrossing. The molecular markers can be utilized for both background and foreground selection after every back cross, to have higher Si accumulation trait in the elite cultivar. For background selection markers will be selected randomly from all 12 rice chromosomes of rice genetic map. It will be desirable to select the markers in such a way that whole chromosome is covered (equal distributed markers). Such marker should show polymorphism among the parents. And for foreground selection the already mapped markers can be uitilised (RM5303 and E60168) along with fine mapped markers that can be identified from the rice genetic map. It is desirable to go for selection after every back cross, so that after three backcrosses and selfing (BC3F3), we can get the plants with desirable trait (higher Si accumulation). The strategy is explained in Figure 1.


Figure 1 Molecular Marker Assisted Backcrossing for transferring of high Si accumulation trait in an elite cultivar

1.2 Proteomics based strategy to identify novel proteins induced due to application of Si
In this approach, it will be possible to resolve and identify all the proteins that get differentially regulated by application of Si. 2-DGE (two dimensional gel electrophoresis) is the best and easiest way to identify the differentially expressed proteins, by comparing the 2D gel profiles of proteins extracted from plant samples (Si+ and Si-). Once we have these profiles, we can easily locate the proteins whose expression is enhanced as well as reduced due to application of Si. An alternative approach can be 1D shotgun proteomics analysis using tandem mass spectrometry (LC-MS/MS). By means of MS these proteins can be identified and their functionality can be determined using various bioinformatics tools and such proteins can be assigned to various metabolic pathways. As such it will help us in understanding the actual impact of Si on various metaboltic pathway which may unlock the secret of potential versatility of this micronutrient and will help us in fully exploring the potential of Si. The strategy is explained in Figure 2.


Figure 2 Proteomics based approach to decipher the role of Si in giving tolerance to various stresses

Authors' contributions
SMZ and MN wrote the paper, GKA and RR also read the manuscript and revised it. All authors had read and consented the final text.

Acknowledgements
SMZ is grateful to the Vice Chancellor, SKUAST-J (Dr. B. Mishra) for providing necessary facilities.

Reference
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Bouman B.A.M., and Tuong T. P., 2001, Field water management to save water and increase its productivity in irrigated rice, Agricultural Water Management, 49(1): 11-30 doi:10.1016/S0378-3774(00)00128-1

Epstein E., 1994, The anamoly of silicon in plant biology, Proc. Natl. Acad. Sci. USA, 91(1): 11-17 doi:10.1073/pnas.91.1.11

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Zargar S.M., Nazir M., Agrawal G.K., Kim D.W., and Rakwal R., 2010, Silicon in plant tolerance against environmental stressors: Towards crop improvement using Omics approaches, Current Proteomics, 7(2): 135-143 doi:10.2174/157016410791330507

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