Defensin molecules are widely distributed in plants and are characterised by their overall structure and shape.
Figure 4.3 Representation of defensin structure. The 5 kDa floral defensin peptide consists of an α-helix with triple stranded anti-parallel ß-sheet stabilized by 4 disulphide bonds (not shown)
The technology was initially tested in the laboratory. The gene was then transferred to cotton plants and tested in the glasshouse against the two fungal pathogens which cause fusarium wilt and black root rot, with positive results. Hexima then received regulatory approval to test the technology in field trials at various sites in Queensland and New South Wales. The trials involved planting cotton in fields naturally infected with the fungi that cause fusarium wilt, verticillium wilt and black root rot. The trials were planted in the growing seasons of 2006/07, 2007/08 and 2008/09.
In both the 2006/07 and 2007/08 trials, dramatic increases in yield and reduced disease impact on the plants were recorded. Importantly there was resistance to two different diseases, fusarium wilt and verticillium wilt. Furthermore there was no observable detrimental effects on the plants. The third field trial of this technology was planted in October 2008.
Hexima’s fungal resistance program is now progressing in partnership with DuPont, with a focus on developing corn resistant to various fungal pathogens.
A particular defensin was discovered in the female sexual tissues of Nicotiana alata and is believed to protect the female sexual tissues from attack by fungi. This defensin technology specifically targets certain filamentous fungi that are pathogens of plants. It has no effect on yeast or on various animal or insect cells tested to date.
Hexima’s technology covers the use of a particular plant defensin and a method to deliver the defensin to a specific part of the plant cell where it can accumulate to the levels needed for plant protection.