A project undertaken at the School of Biological Sciences, Flinders University, and supervised by Kathleen Soole
Oxidative stress is a consequence of living in an oxygen-rich atmosphere and one of the many challenges that plant’s face during growth and development. It can be exacerbated by environmental stresses such as high temperatures, drought and salinity. Oxidative stress occurs when highly reactive oxygen radicals (Reactive oxygen species, ROS) accumulate in a cell and cause damage to DNA, protein and lipids with dramatic effects that often lead to cell death.
Processes for detoxifying ROS and minimising their production exits in all cells and the presence of these have been linked to better growth in plants in laboratory studies. Global climate change and increasing populations will put pressure on our current agricultural productivity; it has been predicted that we will need a 70% increase in productivity to meet our needs by 2050. This will require us to increase out yields in poorer growing areas and we will need crops that can cope with increased oxidative stress.
Figure 1.
While cultivated crops have been bred for better yields, their gene-pools have become very limited due to the long history of human selection. In contrast, wild species and the progenitors of our current crops have diverse genotypes and can often be found in harsher environments. Their still diverse gene pools suggest that they may have retained genes linked to better oxidative stress tolerance. The aim of this project is to study physiology, biochemistry and genetics of a mitochondrial pathway strongly linked to oxidative stress tolerance, the alternative pathway of respiration in the wild ancestors of bread wheat to gain a better understanding of this pathway and for further application in wheat breeding.
The significance of the project is based on the fact that there is a much wider natural polymorphism of genes encoding tolerance to oxidative stress in wild species and that this knowledge, can be used in the conventional breeding of wheat, to generate more stress tolerant germplasm.
Our overall results show that AOX genes, encoding AOX in wild ancestors, have been preserved during the breeding of commercial varieties like bread wheat and are expressed even under control (or optimal) growth conditions. In these experiments, the AOX gene family responded to signals other than those associated with oxidative stress as expression responded even in the absence of an oxidative stress indicator.
During salinity stress there was a variation in responses and salinity tolerance, i.e. better growth during stress, which was not obviously linked to AOX expression, but possibly linked to AOX protein levels in the tissues before the stress. This needs further confirmation.
Salt-induced gene expression suggests a role for the homeologues of AOX genes originating from the B and D genomes in salinity tolerance. Our analyses of the genetic polymorphisms are consistent with these results. Therefore, the suggestion arises that germplasm from wild diploid accessions of Aegilops speltoides and tetraploid accessions of _T. dicoccoides_could be used for improving growth of bread wheat under stress conditions using conventional hybridisation. However, Aegilops speltoides is not a direct progenitor of the B genome but is the closest currently available species containing the S or Bs genome. Nevertheless, interspecific crossings are possible between wild species and bread wheat which might enrich the genetic polymorphism of AOX and other important genes for the improvement of grain yield and quality in wheat.
Due to the growing human population and a decline in optimal growth environments to produce crops, there is a strong demand to generate new varieties with improved yield under suboptimal growth conditions. The results presented in this project reveal that there is genetic diversity within the existing wild ancestors of wheat that could be utilised to improve current commercially grown wheat varieties.