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Not just a grain of rice: the quest for quality

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A better understanding of the factors that contribute to the overall grain quality of rice (Oryza sativa) will lay the foundation for developing new breeding and selection strategies for combining high quality, with high yield. This is necessary to meet the growing global demand for high quality rice while offering producing countries additional opportunities for generating higher export revenues. Several recent developments in genetics, genomics, metabolomics and phenomics are enhancing our understanding of the pathways that determine several quality traits. New research strategies, as well as access to the draft of the rice genome, will not only advance our understanding of the molecular mechanisms that lead to quality rice but will also pave the way for efficient and targeted grain improvement.

Section snippets

Rice quality is a multi-faceted trait

Rice (Oryza sativa) is the most important food crop in the world, providing over 21% of the calorific needs of the world's population and up to 76% of the calorific intake of the population of South East (SE) Asia. In countries where rice is consumed, traits of grain quality dictate market value and have a pivotal role in the adoption of new varieties 1, 2, 3. Quality traits encompass physical appearance, cooking and sensory properties and, more recently, nutritional value. The value of each

Advances in functional genomics of rice quality

Deciphering the genotype of an individual is key to both understanding and predicting which traits a plant is likely to express in a given environment, as well as to decreasing the time for the development of new varieties [6]. Here, we discuss recent progress in identifying and characterizing some of the genes responsible for the most important traits affecting grain quality – appearance (shape and chalk), aroma, texture, nutritional properties and cooking time (Box 1).

Genetical metabolomics – new opportunities

Although genomics approaches have helped to identify and characterize several genes that determine important grain quality traits, we also seek to understand the regulatory and biochemical pathways that are involved in trait expression and that are responsible for subtle qualitative and quantitative differences in each quality trait. For fragrance, we know that the concentration of 2AP is affected by temperature and pre- and post-harvest management 50, 51, but we know little about the

Future prospects

With the available rice genome sequence information, growing data on metabolic networks, genotype–phenotype associations and gene regulatory networks and the emergence of systems biology approaches [63], the rice community is poised to make major advances in our understanding of the molecular, genetic and biochemical bases of important grain quality traits. We live in a time of grave concern about world hunger, shortages in fuel and water, impact of climate change, population growth and future

Acknowledgements

This article has arisen from an International Workshop on Metabolomics and Quality Rice, held in Vientiane, Lao PDR in May 2008, organized by the EU project META-PHOR (FOOD-CT-2006–036220) and the INQR. M.A.F. and R.D.H. acknowledge financial support from the European Union for this collaboration. R.D.H. acknowledges additional support from the Centre for BioSystems Genomics and The Netherlands Metabolomics Centre, initiatives under the auspices of the Netherlands Genomics Initiative. M.A.F.

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