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 and Monsanto, with a focus on developing corn, soy and wheat resistant to various fungal pathogens. Read more about our ‘path to market’ here.
Hexima’s technology was originally developed based on a defensin that was discovered in the female sexual tissues of Nicotiana alata. This protein’s natural function is to protect the female sexual tissues from attack by fungi. The defensin specifically targets certain filamentous fungi that are pathogens of plants. Hexima’s research into how this defensin kills fungi led to the discovery that the defensin permeabilises the plasma membrane. The plasma membrane acts as a protective barrier to cells that prevents most molecules from entering. By making the fungal plasma membrane permeable, defensin allows other molecules that normally have no effect on the growth of fungi to enter and kill the fungal cells. This leads to a synergistic effect whereby both proteins can be applied at much lower concentrations to achieve the same level of fungal control. This discovery has led to significant new IP that is being applied in the fungal disease program. Importantly, Hexima has demonstrated that this technology works in transgenic plants which provides a significant step forward for the disease program.
Hexima has also developed improved variants of its lead defensins that are more effective in vitro and also provide improved activity in transgenic plants.
Hexima’s MGEV technology complements the defensin technology and can be used to produce multiple antifungal proteins in plants using a single gene construct.