Towards a more sustainable wheat

The world is facing an immense challenge to increase food productivity for its growing population. As phosphorus (P) fertilizers are essential for growing our food, annual consumption of P fertilizers has increased rapidly in the past decades and is expected to increase by 50–100 % by 2050. However, the majority of P applied to soil is immobilized and becomes unavailable for plants and the recovery of applied P by crops in a growing season is often low. Furthermore, P fertilizer is mainly made from the non-renewable phosphate rock, which is expected to run out in the near future. Systematic approaches need to be made to use soil P and fertilizer P sustainably and efficiently, including development of P-efficient crop varieties. Genetic differences in P use efficiency exist among plant species and genotypes within a species, showing that it is possible to improve P use efficiency of plants through a genetic approach. Conventional plant breeding methods have been shown to be successful in breeding crops with improved P use efficiency.

Wheat is one of the most important food crops in the world. Worldwide wheat production annually consumes 6·5 Mt of P2O5 (approx. 40 % of P used by cereal crops), much higher than used by other cereals, including rice and maize. Therefore improving P use efficiency of wheat is important in sustainable use of P resources. To breed wheat with improved P use efficiency, understanding the Pi signalling network in wheat is important. Only a few Pi starvation-inducible genes have been cloned and their expression patterns have been analysed, thus the Pi signalling network in wheat remains largely unknown. Although improving P use efficiency via transgenic modification has been reported in a number of crops, studies of transgenic wheat with improved P use efficiency are still lacking.

In the signalling network in sensing P availability, the MYB-CC (coiled-coil) type transcription factor PHR1 plays a central role. A recent paper in Annals of Botany examines three wheat PHR1 genes with homology to Arabidopsis PHR1, and characterizes their role in regulating the Pi starvation response. Ta-PHR1-A1 is involved in Pi signalling in wheat and, when over-expressed, it increased P uptake and grain yield of wheat. This important research promotes the understanding of Pi signalling in wheat, and provides valuable gene resource for breeding wheat with improved P use efficiency and yield.

A phosphate starvation response regulator Ta-PHR1 is involved in phosphate signalling and increases grain yield in wheat. (2013) Annals of Botany 111 (6): 1139-1153. doi: 10.1093/aob/mct080
Phosphorus deficiency is a major limiting factor for crop yield worldwide. Previous studies revealed that PHR1 and it homologues play a key role in regulating the phosphate starvation response in plants. However, the function of PHR homologues in common wheat (Triticum aestivum) is still not fully understood. The aim of the study was to characterize the function of PHR1 genes in regulating phosphate signalling and plant growth in wheat. Wheat transgenic lines over-expressing a wheat PHR1 gene were generated and evaluated under phosphorus-deficient and -sufficient conditions in hydroponic culture, a soil pot trial and two field experiments. Three PHR1 homologous genes Ta-PHR1-A1, B1 and D1 were isolated from wheat, and the function of Ta-PHR1-A1 was analysed. The results showed that Ta-PHR1-A1 transcriptionally activated the expression of Ta-PHT1.2 in yeast cells. Over-expressing Ta-PHR1-A1 in wheat upregulated a subset of phosphate starvation response genes, stimulated lateral branching and improved phosphorus uptake when the plants were grown in soil and in nutrient solution. The data from two field trials demonstrated that over-expressing Ta-PHR1-A1 increased grain yield by increasing grain number per spike. TaPHR1 is involved in phosphate signalling in wheat, and was valuable in molecular breeding of crops, with improved phosphorus use efficiency and yield performance.