Quinoa (Chenopodium quinoa) is a pseudocereal originated from the Andes of America, domesticated as early as 7000 years ago. Its grains, which contain very balanced nutritional contents, contribute to the globally increasing cultivation, and thus are chosen by NASA as a food source for astronauts. 

In addition, quinoa exhibits excellent slat tolerance. Though grown normally under non-saline environment, it achieves the highest biomass in the presence of 100 mM sodium chloride and the biomass decreases by only 20-50% in the presence of 500 mM sodium chloride (seawater level). Thus it was proposed that quinoa cultivation can allow efficient utilization of saline lands and contribute to food security in the future. 

Recently, a collaborative study led by Dr. ZHANG Heng and Dr. ZHU Jiankang at Shanghai Center for Plant Stress Biology (PSC), Shanghai Institute of Plant Physiology and Ecology of Chinese Academy of Sciences and Dr. HEDRICH Rainer from University of Wuerzburg, Germany, revealed the molecular basis of salt tolerance and high nutritional value in quinoa through genomic and transcriptomic analyses. The finding was published in Cell Research. 

The organism of quinoa experienced a whole genome duplication event about 4.3 million years ago. The researchers generated a high-quality genome assembly of quinoa through hybrid assembly of second generation and third generation high throughput sequencing data with a total length of 1.34 Gb and scaffold N50 at 1.16 Mb. 

Genome annotation revealed 54,438 protein-coding genes and 192 microRNA genes. Among the expanded gene families were genes involved in ion and nutrient transport, ABA homeostasis and ABA signaling. The three main families of seed storage proteins all contained significantly higher proportions of essential amino acids than other cereals, partly explaining the high nutritional value of quinoa grains. 

Epidermal bladder cell (EBC) is present in about half of all halophytes and plays important roles in the salt tolerance of quinoa. Previous studies indicated that the volume of EBCs could be 1000-fold of that of normal epidermal cells and the accumulated ion concentration of EBCs could be as high as 1 M. By comparing the gene expression in the EBC, leaf without EBC and the whole leaf, the researchers found that EBC exhibited a very different transcriptome profile compared to other tissues of quinoa and showed high expression in genes involved in wax biosynthesis and sugar transport. 

Further studies also identified multiple ion transporter genes that are specifically expressed in EBCs, whose expression was not affected by salt treatment of quinoa, suggesting that the transporters are constitutively active or regulated at the post-translational level. Based on these results, the researchers proposed a molecular model that helps explain the ion movement from epidermal cells to bladder cells in quinoa. 

The study was funded by Chinese Academy of Sciences, Ministry of Science and Technology of China, China National Science Foundation and Australian Research Council.