Periodic Reporting for period 1 - PMTFOS (Plant metallothioneins as potential players in food security)
Reporting period: 2017-08-01 to 2019-07-31
The overall objective of the PMTFOS project was the comprehensive analysis of the whole family of metallothioneins in Sorghum bicolor. Sorghum is a remarkable crop currently widely cultivated in arid and semi-arid regions of the world due to its unusual drought and heat resistance. More frequent and more widespread drought incidence will likely lead to more global usage of this crop in the future. A cross-disciplinary approach from whole-organism studies to the level of individual proteins was exploited to determine the potential of sorghum metallothioneins for zinc/cadmium discrimination and further for biofortification purposes.
To gain further insight into mechanisms of zinc/cadmium discrimination, site-directed mutagenesis was used to generate proteins with changed amino acid composition. Those mutant proteins were analysed by ESI-MS, elemental analysis and NMR techniques. These mutated proteins had higher specificity towards cadmium and hence no ability to discriminate between zinc and cadmium. Transgenic Arabidopsis plants overexpressing those proteins were also created. Crucially, the plants harbouring mutant proteins accumulated more cadmium and were more tolerant towards cadmium. This confirmed the potential of the original sorghum MT4 protein in discrimination between zinc and cadmium in seeds.
Plant metallothioneins are not only metal-binding proteins but are also considered as stress response proteins. Increased amounts of reactive oxygen species (ROS) are a consequence of most stress conditions including drought. We found that Zn-SbMT4 was able to react with ROS and diminished their reactivity which suggested that MTs may act as antioxidants and hence be linked to fundamental stress responses in plants. Transgenic Arabidopsis plants that overexpress all sorghum MTs separately were created, and their tolerance towards different stress conditions is currently being evaluated.
The PMTFOS project was disseminated in non-scientific publications i.e. “Sorghum during drought: protein protect against withering” on the Science in Poland web page and “Boosting nutrients in crops to beat ‘hidden hunger’ of poor diet” in Horizon: the EU Research & Innovation Magazine. The results obtained during the realization of the PMTFOS project were presented on national and international meetings and conferences i.e. 14th Zinc-Net Meeting in Cambridge (poster presentation) and 7th International Symposium on Metallomics in Warsaw (talk). Currently manuscripts for peer-reviewed scientific journals are being prepared.
The PMTFOS project filled the existing knowledge gap about metallothioneins in the economically important staple crop sorghum. A cross-disciplinary approach combining bioinorganic chemistry, molecular biology and plant science was used to comprehensively analyse the whole family of MTs in sorghum. Coherent biophysical data combined with in planta results for the entire family of MTs from a single plant species did not exist before. In addition, CRISPR/Cas9 genome editing was used for the first time in determining the physiological roles of plant metallothioneins.