ACPFG research recently published in PLoS One descibes a model explaining how ancestral rice plants survive saline soils. Agricultural lands worldwide are getting saltier, and in Australia this is a particular problem in WA and SA.
Associate Professor Maria Hrmova described the impacts of her research on the ABC Rural SA Country Hour (listen to the podcast from 17 min for her interview). She explains that understanding how some rice plants are more salt tolerant than others will help develop salt-tolerant cereal varieties.
The research shows that the salt-tolerant rice plants use a genetic mutation and alternative splicing to improve the efficiency of two sodium transporters. The transporters prevent salt accumulating in growing leaves, where too much sodium causes growth defects and low yield. They do this by keeping salt out of roots, and moving it into older leaves.
All rice plants carry the genes for these sodium transporters, but it’s a naturally-occurring genetic mutation that helps some plants tolerate salt. The mutation makes the sodium transporters more efficient by changing the structure at the entrance of the pore. Sodium can move through the mutated transporter more efficiently because of a smaller amino acid at the mouth of the pore.
The structure video shows the sodium ion as a sphere inside the colourful protein which forms the sodium transporter. The parts of the protein shown as pink sticks are the amino acids at the mouth of the transporter. When one of these amino acids carries a naturally-occuring mutation the transporter becomes more efficient at carrying sodium.
Rice plants use different sodium transporters in their roots and shoots. In the roots, HKT1;5 removes sodium before water is transported to the leaves. Plants carrying the HKT1;5 mutation remove more salt than plants without the mutation.
In the shoots it is HKT1;4 that moves salt into older leaves instead of growing leaves. Depending on the age of the leaf, plants produce more mRNA copies of the gene encoding the sodium transporter protein. Plants also regulate the amount of salt in leaves by splicing the gene transcript to form either functional or faulty transporters.
Understanding the mechanisms of sodium exclusion from leaves will help plant scientists to provide the farming industry with cereal varieties that can survive in saline soils. Further studies will investigate whether this model can be applied to other food crops including wheat and barley.
The research is from the Structural Biology group led by Maria Hrmova. This article was written by Arwen Cross.
The authors on the paper are: Olivier Cotsaftis, Darren Plett, Neil Shirley, Mark Tester and Maria Hrmova.