Soil salinization is becoming a big problem for modern agriculture by affecting crop yield and quality. Some plants have evolved delicate mechanisms to deal with salt stress during their colonization in saline habitat. Identifying the genetic basis underlying these mechanisms is not only critical for understanding natural selection and evolution, but can also help relieve the soil salinization problem.

Arabidopsis thaliana is a model plant that is widely distributed in the world. Previous studies have established that the natural accessions accumulating high sodium in the leaves are enriched in coastal and saline areas. Weak expression of Arabidopsis thaliana high-affinity potassium transporter 1 (AtHKT1) encoding a sodium transporter is responsible for the high leaf sodium in these accessions, and was then hypothesized to drive local adaptation to saline environments in A. thaliana.

However, high leaf sodium was believed to be a salt-sensitive symbol and AtHKT1 was previously found to be essential for salt tolerance of A. thaliana. These contradictive results make it more compound if and how AtHKT is involved in saline adaptation of A. thaliana.

Recently, a research group led by Prof. CHAO Daiyin at Shanghai Institute of Plant Physiology and Ecology, CAS Center for Excellence in Molecular Plant Sciences, Chinese Academy of Sciences, uncovered the mystery underlying the role of AtHKT1 in salt tolerance. The work was published in PLOS GENETICS.

Using forward and reverse genetics, researchers confirmed for the first time that AtHKT1 plays a key role in local adaptation of the coastal line Tsu-1 in saline habitat. They used a unique technology, reciprocal grafting experiment, to establish that shoot is more important for salt tolerance of Tsu-1 while root plays a major role in salt tolerance of the inland A. thaliana accession Col-0.

Further analysis showed that, under salt stress, the expression level of AtHKT1 in Tsu-1 stems is much higher than in Col-0 stems, indicating that AtHKT1 is hyper-functional in stems but hypo-functional in roots of the salt tolerant accessions.

Ionomics analysis revealed that the floral sodium content is significant in Tsu-1 then in Col-0 upon salt stress, establishing that AtHKT1 in Tsu-1 is more efficient in retrieving sodium flow to the flower, an essential but salt sensitive organ for productivity.

Together with other evidence, the results demonstrated that the coastal accessions, in the process of adapting to saline habitats, have evolved a new mechanism by upregulating expression of AtHKT1in shoots to reduce sodium toxicity to the flowers. This study not only addresses an important scientific question of evolution biology, but may also open a new angle for engineering salt tolerance crops.

This study was supported by the National Nature Science Foundation of China, National “1000-youth talents” program, the Strategic Priority Research Program of the Chinese Academy of Sciences and National Key Laboratory of Plant Molecular Genetics.