Gene Switch Makes Sweet Sorghum Salt-Tolerant

By Sandra Wiebe

Sorghum millet is seen as the crop plant of the future: It builds up a particularly high amount of biomass and thrives in harsh conditions. Certain varieties even produce more sugar on salty soils.

In an in-depth investigation of this salt-stress-induced sugar accumulation conducted by an international team including scientists from Karlsruhe Institute of Technology (KIT), it was found that the SWEET13 gene switch is responsible for directing sugar into the grains.

Targeted breeding allows the introgression of SWEET13 into different varieties of sorghum millet so that it contributes to the food security of humankind. The researchers reported on their findings in Scientific Reports.

The world's population is growing, and with it, the demand for food, primary products, and energy. Thus, crop productivity, especially that of cereals, needs to increase significantly. The impact of climate change renders it progressively difficult to meet this goal.

Besides heat and drought, soil salinity puts crop plants under stress, as more and more fertile grounds are becoming salty because of the rising sea levels. Crop plants, which both have a high amount of biomass and thrive well on saline soils, might mitigate this problem.

The Molecular Cell Biology Division workgroup, headed by Professor Peter Nick at KIT's Joseph Gottlieb Kölreuter Institute for Plant Sciences (JKIP), has been working for some years on sorghum millet, which belongs to the millet species in the sweet grass family. The sorghum varieties rich in sugar are called sweet sorghum.

Sorghum millet is one of the crops with a particularly efficient photosynthesis process, which have a higher capacity to sequester carbon dioxide (CO₂) and build up more biomass than other plants. Previous research by Syrian scientist Dr. Adnan Kanbar at KIT resulted in the development of a new sweet sorghum variety that accumulates a particular large amount of sugar and is well-suited for producing biogas and biofuels and for producing new polymers.

Certain varieties produce more sugar on saline soils

Further research shows that sorghum millet, an ancient crop plant from Sudan, thrives even in harsh conditions. "Certain sorghum millet varieties not only cope well in a saline environment, but react to increased salinity with the production of even more sugar," says Nick.

"Some of these varieties store the sugar in the stem, which makes them a candidate for energetic use, i.e., the production of biofuels. Other varieties store the sugar in the seeds, making them a valuable contribution to human nutrition."

SWEET13 gene switch directs sucrose toward the grains

This salt stress-induced sugar accumulation and the different ways to store sugar in the plant was investigated by a group of researchers led by Dr. Eman Abuslima from Egypt, who completed her doctorate at the Molecular Cell Biology Division workgroup of KIT's JKIP institute. They discovered that the SWEET13 gene is responsible for sugar transport.

"SWEET13 works like a switch: It determines that the sucrose formed by photosynthesis is directed into the plant's grains," explains Abuslima. The researchers found a particularly active type of SWEET13 in Razinieh, an ancient sorghum millet variety from Syria.