It is important that biosafety of any transgenic approach is considered and only fully biosafe transgenic plants are developed beyond the proof-of-concept stage. Past work has established that the rice cystatin used in potato and banana is not a toxin and the growing plants do not harm a range of non-target organisms. Work is also continuing to develop the same level of information about the safety of the peptide. The search for reliable and rapid means of defining the environmental impact of transgenic plants has led to study of soil nematodes because they respond predictably to land management changes that reflect changes in soil microenvironments. A standard method of nematode faunal analysis allows the enrichment and structure of the food web to be inferred for genera that respond rapidly to environmental change (enrichment index) and those that prefer undisturbed habitats (structural index). We have shown peptide and cystatin expressing plants do not alter these values more than non-transgenic crops suggesting they are not environmentally hazardous.
Tissue-specific promoters for trangenic plants can deliver cystatins to the feeding sites of cyst and root-knot nematodes. The peptides can also be targeted appropriately using the MDK4-20 promoter of Arabidopsis thaliana which is active in root tips and also the root border cells that detach from the roots of many crops. Effective, specific promoters lower the burden of biopesticide production in other plant tissues, reduce any hazard to non-target organisms and enhance food safety when expression is minimized in the harvested yield.
RNAi could have effects on non-target organisms if there is sufficient homology between the target gene of the nematode and that in other, non-target organisms. Sequence homology of novel, small RNAs to genes that are not the intended silencing targets may also lead to off-target effects. Both of these considerations could be compounded if small RNA molecules are shown to have prolonged environmental persistence.