Deepwater rice carries genes called SNORKEL that help it outgrow floods
When floodwater rises, some rice plants race it. In deepwater varieties, two genes named SNORKEL1 and SNORKEL2 trigger rapid stretching of the stem segments, keeping leaves above the surface. Other strains take the opposite approach, using a gene called Sub1A to sit out complete submergence until the water recedes.
Oryza sativa, Asian cultivated rice, is by far the more common of the two rice species grown for grain; the other is African rice. Its genus name comes from the Ancient Greek word for rice, and sativa simply means cultivated. It was first domesticated in China's Yangtze River basin between 13,500 and 8,200 years ago. The plant stands 80 to 120 centimetres tall on a smooth, upright stem with narrow, pointed leaves.
Two main subspecies dominate. Japonica, short-grained and sticky, came out of the Yangtze Valley 6,000 to 9,000 years ago and can grow in dry fields, from temperate East Asia to South Asian highlands, although Japan mostly floods its paddies. Indica, long-grained and not sticky, was domesticated near the Ganges 4,500 to 8,500 years ago and is mainly grown submerged across tropical Asia. A third, broad-grained form once called javanica is now known as tropical japonica; examples grow on the mountain terraces of northern Luzon in the Philippines. Grains can be white, brown, red or black, the last turning purple when cooked.
Scientists prize the species as a model for cereals. Its genome, about 430 million base pairs over 12 chromosomes, is relatively easy to modify. Genetic surveys have sorted cultivated rice into five groups, a scheme that still held up in 2019, and researchers have catalogued 641 copy number variations. Some versions of a gene called SPL14 reshape the plant's architecture and raise yields.
Defence is written into the genome too. Genes including Pi54 and Pita protect against rice blast fungus, and the plant balances two hormones to manage that immunity: salicylic acid boosts it while abscisic acid dampens it. By 2022, 15 resistance genes against the brown planthopper, an insect pest, had been cloned and characterised.
Source: Oryza sativa
