Eukaryotes Genomes - ORYZA SATIVA

Oryza sativa (rice) is one of the most important crops in the world and it provides the main resource of energy for more than half of the world population and is the major food crop in China.

Oryza sativa is a kind of grass, which grows best when submerged in water. It grows in upland areas, irrigated areas, rainfed lowland areas, and flood-prone areas. Rice is highly adaptable and can be grown even in diverse environments. It resembles a weed, 2 to 5 feet tall, depending on the variety and depth of submersion. It has round, hollow, jointed stems, rather flat, sessile leaf blades, and a terminal panicle. The grain is produced on nodding panicles of spikelets. It looks like a smooth glistening ovoid particle, emerald green in color (during ripening stage, however, it turns golden yellow). After it is milled, the kernel will appear shiny white in colour.

The origins of rice have been debated for some time, but the plant is of such antiquity that the precise time and place of its first development will perhaps never be known. It is certain, however, that the domestication of rice ranks as one of the most important developments in history, for rice is the longest, continuously grown cereal crop in the world. Botanical and linguistic evidence point to the early origin of domesticated rice along a broad arc from eastern India through Myanmar, Thailand, Laos, Northern Vietnam, and into southern China. The earliest and most convincing evidence for domestication of rice in Southeast Asia was discovered in 1966 at Non Nok Tha in the Korat area of Thailand. These remains have been confirmed as dating from at least 4000 B.C.

There are about 120,000 varieties known to exist. Two of the types sequenced are Indica and Japonica, the japonica varieties have narrow dark green leaves, medium-height tillers, and short to intermediate plant height. It is usually grown in cooler subtropics and temperate climates, such as Japan, Portugal, Spain, USSR, Italy, and France. The traditional indica rice varieties, widely grown throughout the tropics and subtropics, are tall and heavy tillering with long, narrow, light green leaves.

Oryza sativa was the cereal selected to be sequenced as a priority and has gained the status "model organism". It has the smallest genome of all the cereals: 430 million nucleotides and it can serve as a model genome for one of the two main groups of flowering plants, the monocotyledons. Because it has been the subject of studies on yield, hybrid vigor, genetic resistance to disease and adaptive responses, scientists have taken advantage of the existence of a multitude of varieties that have adapted to a very wide range of environmental conditions, from dry soil in temperate regions to flooded cultures in tropical regions.

Rice production represents 30% of the world cereal production today. It has doubled in the last 30 years, in part due to the introduction of new varieties, but its present growth barely follows consumption: in 2025 there will be 4.6 billion people that depend on rice for their daily nourishment, compared with three billion today. A new leap in production is therefore expected. At the same time, small producers will have to use land which is less favorable for cultivation, such as brackish or briny soils, and the availability of water resources will become more and more problematic.

Two research teams have sequenced related subspecies of rice. Essential biological information from the rice genome will undoubtedly improve our understanding of the basic genomics and genetics of other related and economically significant crops, not only wheat, corn, sorghum, and members of the grass family, but also dicot crops such as soybean and cotton. The finished genomes will take some of the guesswork out of plant breeding as breeders will be able to determine whether a seed contains a particular gene through genetic analysis. If a gene is known to contribute to trait of interest, variants of this gene can be examined in other varieties.

References:

http://www.genoscope.cns.fr/externe/English/Projets/Projet_CC/organisme_CC.html
http://www.plantgdb.org/OsGDB/
http://btn.genomics.org.cn:8080/rice/
http://www.irri.org/about/faq.asp