Defining the Genetic Basis of Rice With low Glycemic Index

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 Background

Rice is the most widely consumed staple food for half of the world's population (Sweeney and McCouch 2007). It serves as the primary source of dietary energy and carbohydrates for most Asians and Africans (IRRI). However, prospective cohort studies in genetically divergent populations show that white rice consumption is associated with increased risk of developing type II diabetes independent of ethnicity (Murakami et al. 2006; Sun et al. 2010).

Type II diabetes is a major global health problem, and its prevalence is increasing dramatically throughout the world, especially in Asia (Chan et al. 2009; Danaei et al. 2011). By 2030, almost 330 million people will be affected by diabetes, and the greatest burden of this disease will be borne primarily by the socioeconomically disadvantaged in low and middle-income societies (Misra et al. 2010; Walgate 2008). Diabetes mellitus deaths in Nepal reached 3,224 or 2.17% of total deaths, and it ranks 115 in the world (WHO, 2011). In a study of middle-aged Chinese women, type II diabetes risk was 78% greater in those consuming more than 300 g rice/day relative to those eating <200 g/day (Villegas et al. 2007). Whereas white rice has been shown to adversely affect metabolic health, brown rice may be protective. While the frontline strategy for primary prevention of type II diabetes is through more judicious food choices, behavioural change, which is sustained and its meaningful magnitude, is difficult to achieve in practice, especially in the short term. Thus, lowering the GI of staple foods such as rice is likely to be more effective in promoting public health, especially in communities in which rice accounts for a large share of dietary glycemic load and where there are entrenched cultural preferences for consumption of white rice. Some Australian, Indonesian, Indian, and Bangladeshi varieties have been reported to have lower GI than other rice, but the genetic basis of GI has not been determined.

Previous studies have shown that high amylose rice varieties generally tend to have a lower glycemic index (IRRI). This implies that, if we can establish which of these high amylose lines consistently score low glycemic indices, and use them to subsequently establish the genetic basis for the trait, then we can assemble a set of pre-breeding materials for parental selection by breeders. Discovering such a rice variety has both medicinal and commercial value that can save thousands of lives, while at the same time controlling the contribution of rice consumption to the postprandial rise in blood glucose levels.

Objectives

1)    To define low glycemic index rice on a genetic basis.

2)    To prepare a set of low GI rice genotypes as a pre-breeding material for parental selection.

3)    To standardize the screening technique to measure the glycemic index of rice varieties.

4)    To identify low glycemic index varieties from popular modern and local improved varieties.

Methodology

Genome-wide association using 700K SNP data will be done as an initial step to identify which genomic regions identified by the SNP markers are associated with the traits of interest. Data from the 3,000 re-sequenced rice genomes that were recently made available in the public domain will then be analyzed to identify the role of genomic variations in controlling glycemic index. Gene expression analysis of developing grains will be the final step to identifying the molecular mechanisms related to lowering glycemic index in rice.

Expected Output

1)    Low glycemic index rice will be identified on a genetic basis.

2)    A set of low GI rice genotypes will be prepared as pre-breeding materials for parental selection.

5)    Standardization of screening techniques to measure the glycemic index of rice varieties.

3)    Identification of low glycemic index varieties from popular modern and local improved varieties

Keywords: low GI, Glycemic index, diabetes, blood sugar, GI, high amylose rice, GI and amylose

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References 

Chan JCN, Malik V, Jia WP, Kadowaki T, Yajnik CS, Yoon KH, Hu FB. Diabetes in Asia: epidemiology, risk factors, and pathophysiology. J Am Med Assoc. 2009; 301:2129–40.

Danaei G, Finucane MM, Yuan Lu, Singh GM, Cowan MJ, Paciorek CJ, Lin JK, Farzadfar F, Khang Young-Ho, Stevens GA, Rao M, Ali MK, Riley LM, Robinson CA, Ezzati M. National, regional, and global trends in fasting plasma glucose and diabetes prevalence since 1980: systematic analysis of health examination surveys and epidemiological studies with 370 country-years and 2.7 million participants. Lancet. 2011;378:31–40.

Misra A, Singhal N, Khurana L. Obesity, the metabolic syndrome, and type 2 diabetes in developing countries: role of dietary fats and oils. J Am Coll Nutr. 2010; 29:289S–301.

Murakami K, Sasaki S, Takahashi Y, Okubo H, Hosoi Y, Horiguchi H, Oguma E, Kayama F. Dietary glycemic index and load in relation to metabolomic risk factors in Japanese female farmers with traditional dietary habits. Am J Clin Nutr. 2006; 83:1161–9.

Sun Q, Spiegelman D, van Dam RM, Holmes MD, Malik VS, Willett WC, Hu FB. White rice, brown rice, and risk of type 2 diabetes in US men and women. Arch Intern Med. 2010; 170:961 9.

Sweeney MT, McCouch SR. The complex history of the domestication of rice. Ann Bot. 2007; 100:951–7.

Walgate, R. Diabetes research for developing countries: European Action on Global Life Sciences (EAGLES). Nature Biotech. 2008; 25:111–16.

IRRI (2016) www.irri.org Retrieved 26 January 2016

(Note: This proposal was developed by Dr. Ujjawal Kr. S. Kushwaha. Please take his permission for further citations.)

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