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Highly Efficient and Thermotolerant Wheat

Periodic Reporting for period 1 - HEAT-WHEAT (Highly Efficient and Thermotolerant Wheat)

Reporting period: 2016-09-01 to 2018-08-31

Issue being addressed

The world is facing more frequent and extreme heat waves. This will have a detrimental impact on important food crops like wheat that are susceptible to heat stress. One of the most susceptible parts of a plant to heat stress is photosynthesis, the ability of the plant to make sugars from water and carbon dioxide fixed from the atmosphere. If photosynthesis is impaired then growth and yield of crops will also be impaired and food production will decline, a major problem considering the need of humans to feed a growing world population.

Importance to society

Wheat along with rice would be one of the greatest contributors to human calorie uptake across the world. Wheat is a selectively bread temperate grass and as such is not able to sustain photosynthesis, growth and yield when temperatures are much above 35 degrees celsius. Considering wheat is grown in temperate climates in Europe, Russia and North America, and such regions are expected to face higher average and more extreme and frequent heat waves, the ability of wheat to maintain current or improved levels of yield will heavily depend on the ability of the crop to withstand these periods of heat stress. In other words, without improved heat stress tolerance of wheat growth and yield the ability of humans to meet the growing food intake of the global human population will be difficalt.

Objectives of project

One of the key components of the susceptibility of photosynthesis to heat stress is an enzyme named Rubisco activase (Rca) which allows the carbon dioxide fixing enzyme Rubisco to stay functional. The key objective of the project was to enhance the thermal stability of the Rca enzyme in wheat so that wheat photosynthesis, growth and ultimately yield will be less susceptible to heat stress.
Initially wild relatives of wheat (i.e. species closely related to wheat but not cultivated by humans for food) from the same genus (Triticum) and a closely related genus (Agelops) was assessed for genetic diversity in the Rca gene that might provide insight into differences in the protein related to thermal tolerance. However, considering Rca is such an important enzyme in the photosynthesis pathway and therefore for survival of the plant, the gene was found to be highly conserved in all species examined and no genetic information of interest was obtained. As such, the project was expanded to include species unrelated to wheat but from warm climates and cold climates to compare differences in genetic sequence between species from these contrasting environments and determine which amino acids of the Rca enzyme are conserved in species from warm habitats. This allowed the identification of amino acids that when incorporated into the wheat Rca enzyme, improved the thermal stability of the enzyme from ~36 degrees celsius to ~42 degrees celsius, a dramatic improvement. Furthermore, the improvement to thermal stability came at no cost to the functionality of the enzyme under standard conditions. Thus, the results provide a tangible approach for improving the heat stress tolerance of photosynthesis and potentially yield of wheat if these changes in amino acid makeup of the enzyme identified by the project are incorporated in the Rca enzyme of wheat. As an auxiliary part of the project we tested the concept of improving growth and yield of rice during heat stress by incorporating a thermally stable rice variant of Rca taken from a wild relative that grows in the hot northern regions of Australia. The results of the rice experiments were encouraging as seed yield of rice improved significantly under heat stress when the thermally stable Rca variant was expressed. The rice experiments were recently published in the journal 'Frontiers in Plant Science'. Another unexpected aspect of this project was the inadvertent finding that a single mutation to the wheat Rca gene could change its regulatory properties, a finding that could improve the efficiency of wheat Rca under all temperatures. The findings on the thermal stability of wheat Rca and the regulatory mutant of wheat Rca are the main results of this project and have been written in manuscript format and are waiting for clearance for publication after intellectual property legal requirements are finalised. An expected publication date is January 2019. The results on wheat Rca thermal stability have already been filed as a provisional patent and the results on wheat Rca regulation are currently being drafter for patent filing. Therefore in total this project will generate three publications in international peer reviewed journals and two patent applications.
The results have allowed for discovery of what is needed to improve the thermal stability of the susceptible photosynthesis protein Rca in wheat by potentially 7 degrees celsius. On the basis of this the project will continue within the host organisation in an attempt to develop and test a wheat cultivar that holds the thermal stable Rca and is heat stress tolerant. If such a wheat cultivar is successfully grown it has the potential to play an important role in wheat production and food security over the coming decades.
Inspecting wheat in the greenhouse