Genome sequencing reveals a plant's adaptation to extreme conditions

The saltwater cress Thellungiella salsuginea is adapted to living in extreme conditions, and thrives in some of the harshest environments on Earth, such as the east coast of China, the Rocky Mountains in America and the hyper-salty Lake Tuz in Turkey.

An international team of researchers led by Qi Xie of the National Center for Plant Gene Research in Beijing, and including Hans Bohnert of King Abdulaziz University in Jeddah, has now sequenced the plant's genome to reveal some of its defence mechanisms.

Xie and colleagues used state-of-the-art high-throughput DNA sequencing technology to examine the T. salsuginea genome and compare it to the genomes of related species, to identify the genes that contribute to its survival in such stressful environments.

Their analysis showed that the T. salsuginea genome contains 28,457 genes and is substantially bigger than that of the thale cress Arabidopsis thaliana, due to multiple duplication events caused by transposable elements, or jumping genes.

These gene duplications increased the number of genes involved in ionic and osmotic equilibrium, contributing to the plant's ability to tolerate high salt concentrations. For example, the T. salsuginea genome contains three copies of the HKT1 gene, which encodes a sodium/potassium transporter protein, whereas that of A. thaliana has just one.

Similarly, T. salsuginea has an extra copy of the gene encoding cytochrome-P450-dependent midchain hydroxylase, an enzyme involved in the synthesis of a waxy substance found in the leaf cuticles, which protects against drought.

"This information will enable us and other researchers to perform more detailed analyses and comparisons to further reveal the mechanisms of adaptive evolution," says Xie. "We will continue to perform such analyses to find key genes contributing to stress tolerance. Cloning these genes could help to improve stress tolerance in crop plants."

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