Risk Assessment and Risk Management Plan

Section 3 Conclusions regarding toxicity and allergenicity

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Section 3 Conclusions regarding toxicity and allergenicity

  1. It is considered that the risk of the GM papayas in the proposed release being more toxic or allergenic to humans or other organisms than non-GM papayas is low because:

  • the GM papayas are not likely to become more toxic or allergenic than non-GM papayas as a result of the introduced proteins or the down-regulation of ethylene biosynthesis or altered ethylene perception;

  • the introduced proteins, or naturally occurring proteins that may have altered expression levels, are not likely to be toxic or allergenic in themselves;

  • available data to date suggest that the risk of toxicity and allergenicity is low but detailed toxicity and allergenicity studies have not yet been conducted;

  • exposure of humans and other organisms to the GM papayas will be minimal due to the limited scale and enclosure of the trial within an insect-proof enclosure that also prevents wildlife that may feed on papaya fruit and other animals from entering the release site;

  • none of the GM material from the release will be used for human or animal consumption; and

  • fruit produced during the release will be removed from the site to prevent fruit proteins from entering the soil;

  1. As a condition of licence, the University of Queensland must report any adverse effects on human health and safety or the environment (for example allergic reactions as a result of occupational exposure to the papaya).

  2. Further data on the toxicity and allergenicity of the introduced proteins and the GM papaya would be required for any potential future approval for release of GM papaya with delayed fruit ripening (which would be subject to separate applications and assessments) intended for human or animal consumption.

appendix 3 ENVIRONMENTAL SAFETY – Weediness

  1. Under section 51 of the Act, the Regulator is required to consider risks to human health and safety and the environment in preparing the risk assessment and the risk management plan. Appendices 2-4 consider potential hazards that may be posed to the environment. The potential weediness of the GMO is considered in this Appendix.

  2. There are numerous definitions of weeds including ‘a plant growing where it should not be’. Weeds become a problem to the community when their presence or abundance interferes with the intended use of the land they occupy. Weed impacts on biodiversity may occur directly, via direct competitive displacement of more desirable species or indirectly, on various trophic levels within the community, by altering the structure of food webs.

Section 1 Nature of the weediness hazard

  1. The possibility was considered that the GM papayas might have the potential to be harmful to the environment because of increased potential for weediness, either as a direct result of the genetic modification, or as a result of pleiotropic effects. This could result in increased fitness due to increased seed production, establishment, growth rate, persistence or potential for dispersal, or enhanced pathogen or herbivore resistance. If the GM papayas were to persist and spread in the environment as a weed, this could result in impacts such as loss of native biodiversity or adverse effects on agricultural systems.

Section 2 Likelihood of the weediness hazard occurring

Section 2.1 Weediness of non-GM papaya

  1. In Australia, C. papaya is not considered to be a problematic weed of either agriculture (Groves et al. 2002) or of the natural environment (Groves et al. 2000). Although this species has naturalised in some tropical and sub-tropical areas of the continent (Australia’s Virtual Herbarium 2003; Randall 2002), it does not appear to impact significantly on native biodiversity (Groves et al. 2000).

  2. Vasconcella pubescens (formerly C. pubescens) is the only close relative of papaya that has been recorded as a weed (Randall 2002). These reports indicate that weedy infestations are apparently limited to certain tropical islands and localised areas of New Zealand (Randall 2002) and that at worst, the species is only considered to be ‘moderately invasive’ (see references in Randall 2002).

  3. There are no records of V. pubescens (or other Vasconcella species) in any Australian herbaria (Australia’s Virtual Herbarium 2003) and no evidence from key Australian horticultural literature (see, for example, Elliot and Jones 1980) that these species are being cultivated in Australia. While it is possible that locally, V. pubescens (and related species) may begrown in Australia, there is no evidence that the species is widespread or is a problematic weed of either agriculture or the natural environment (Groves et al. 2000; 2002).

  4. More detailed information on the weediness of papaya can be found in a review document ‘The Biology and Ecology of Papaya (paw paw), Carica papaya L., in Australia’ that was produced in order to inform this risk assessment process. This document is available at the OGTR website (http://www.ogtr.gov.au).

Section 2.2 Potential for enhanced weediness of the GM papayas

  1. Potentially, the GM papayas proposed for release could be at a selective advantage, which may enhance their weediness, if traits such as competitive ability, growth rate, seed production, germination or seed dormancy are affected by the genetic modifications. Similarly, if resistance to pathogens or tolerance of herbivores is affected by the genetic modifications, the papayas may have increased potential for weediness.

2.2.1 Effects of modified ethylene biosynthesis on weediness

  1. The applicant has indicated that, other than delayed fruit-ripening, it is not expected that down-regulation of ethylene biosynthesis would affect other ethylene-related processes in the GM papayas modified with the ACC synthase genes. As summarised in Appendix 1, however, ethylene influences a number of processes in plants and these may also be affected in the GM papayas, particularly because the introduced ACC synthase genes are under the control of the 35S promoter (see Appendix 1, Section 3.5). Although down-regulation of ethylene production in fruit or other plant tissues is unlikely to affect attributes of the GM papayas that affect their weedy potential, the Regulator has been unable to determine this conclusively in the absence of evidence regarding the functioning and impact of the introduced ACC synthase genes in different plant tissues.

2.2.2 Effects of modified ethylene perception on weediness

  1. Genetic modifications to the ability of some of the GM papayas to perceive ethylene may also modify other processes in the GM papayas, with potential to affect weediness. For example, Arabidopsis thaliana plants with altered ethylene perception due to expression of a non-functional version of the etr1 gene germinated at very low rates compared to ‘normal’ A. thaliana seeds (Bleecker et al. 1988). Decreased germination rates imply a potential for seeds to accumulate in the soil seed bank and persistent soil seed banks are an attribute of many weed species (Baker 1965; Noble 1989; Williamson & Fitter 1996).

  2. As papaya only reproduces by seed (Nakasone & Paull 1998), potential development of a persistent soil seed bank may affect the weedy potential of the GM papayas proposed for release. Accordingly, future applications to release the same types of GM papayas (which would be subject to separate applications and assessments) would require investigation of the germinability of GM papaya seeds and determination of the impact of altered ethylene perception and biosynthesis on key ethylene-related processes within the plant, before any such application could be considered. The Regulator would also require information regarding the extent and persistence of a C. papaya soil seed bank associated with the known naturalised populations of papaya in Queensland, in the event of any future application to release the GM papayas on a larger scale. There appears to have been few published investigations of papaya soil seed banks, but the potential for their development is clear (Perez-Nasser & Vazquez-Yanes 1986) and they are an attribute of papayas that enable establishment in some disturbed habitats (Kwit et al. 2000).

  3. Disrupted ethylene perception in ethylene-insensitive A. thaliana led to a 25% increase in the size of some leaves, delayed senescence of some leaves and delayed production of mature flowers (Bleecker et al. 1988). Potentially, modifications of this type in the ethylene-insensitive papayas proposed for release may affect their capacity to tolerate herbivory. For example, if leaf area is increased significantly, the area of leaves damaged by herbivores may be a relatively low proportion of the total leaf area in the GM plants. Alternatively, disruption of ethylene perception may alter plant defence responses to herbivores, thereby affecting tolerance of herbivory. Nonetheless, it should be noted that, compared with fungal and viral pathogens, arthropod herbivores are relatively minor pests of commercial papaya plantations (see OGTR 2003) and are unlikely to significantly affect the persistence and spread of potentially weedy papaya plants.

  4. Increased leaf area associated with disrupted ethylene perception may also modify competitive ability and, thereby, affect potential weediness. It is well-known, for example, that increased leaf area affects competition between neighbouring plants (Garrity et al. 1992; Van Delden et al. 2002).

  5. Ethylene also plays a role in the defence response of plants challenged by microbial pathogens. As detailed in Appendix 1, ethylene insensitivity has led to increased susceptibility to some pathogens (Thomma et al. 1999; Norman-Setterblad et al. 2000; Ton et al. 2002) and to some normally non-pathogenic microorganisms (Knoester et al. 1998; Knoester et al. 1999; Geraats et al. 2002). Conversely, ethylene insensitive plants, and plants with down-regulated ethylene production, have reduced symptoms in response to some normally pathogenic organisms (Wubben et al. 2001; Lund et al. 1998; Bent et al. 1992). If pathogens are a major limitation to the spread and persistence of C. papaya in natural Australian ecosystems, the ethylene insensitivity conferred by the etr1 1 gene may confer a selective advantage leading to enhanced weediness. Future applications to release the same types of GM papayas would require data regarding the impact of limiting ethylene perception (and of down-regulating ethylene production) on the response of the GM papayas to susceptibility to key pathogens, before the application could be considered.

  6. The applicant has indicated that the etr1 1 gene introduced into the GM papayas proposed for release will be controlled by a fruit-specific promoter (pga; see Appendix 1, Section 3.5). Accordingly, etr1 1 is only expected to be expressed in tissues associated with papaya fruit and it is unlikely that ethylene-related processes in other papaya tissues would be affected by its introduction. While leaf area, for example, may not be affected by ethylene-insensitivity because of the fruit-specific promoter driving expression of etr1 1, characteristics of the seeds, which are born by fruit, may be affected. In the absence of evidence regarding either the introduction and functioning of the etr1 1 gene, or the effectiveness of the pga promoter in limiting its expression to fruit tissues, the Regulator is unable to determine conclusively that the GM papayas with altered ethylene perception do not have potential for enhanced weediness.

2.2.3 Effect of antibiotic resistance and GUS expression on weediness

  1. The antibiotic resistance nptII gene will not confer a selective advantage on the GM papayas, since antibiotics are not applied to papayas and there is no reason to expect that expression of the protein would alter any of the characteristic attributes of papaya that would be important for weediness. Similarly, the GUS protein is extremely unlikely to confer any selective advantage on the GM papayas that might result in weediness (Gilissen et al. 1998).

Section 2.3 Spread of GM papayas in the environment
      1. Spread of pollen from the GM papayas

  1. In Queensland, most C. papaya fruit are produced following cross-pollination by hawkmoths (Lepidoptera: Sphingidae) (Garrett 1995; Morrisen et al. 2003) (see Appendix 4). To prevent pollen flow from the release site the applicant has proposed to contain the whole release area in an insect-proof enclosure designed to eliminate access to the GMOs by key pollinating insects. The genetic modifications to the papaya plants proposed for release are unlikely to alter the dispersal of papaya pollen or other aspects of its pollination biology. Licence conditions require that this enclosure is monitored regularly and that any damage is repaired immediately.
      1. Spread of fruit and seeds from the GM papayas

  1. Other than human transportation of papaya fruit, the most likely means of C. papaya being dispersed in the environment is by flying foxes (Poliocephalus spp.). The applicant has indicated that flying foxes are the chief mammalian predators of papaya in Australia and, therefore, the most likely non-human dispersers of papaya seeds. Potentially, however, a range of other species could aid papaya fruit and seed dispersal including other bats, various other mammals including rodents and possums, and some birds.

  2. The genetic modifications to the papaya plants proposed for release are unlikely to alter the dispersal of papaya fruit and seeds. However, if fruit ripening is delayed and fruits are retained on trees for longer, they may be available to frugivores that disperse the fruit for longer periods of time. Delayed fruit ripening traits may also make the fruit a less attractive food resource and, potentially, may decrease the natural dispersal patterns of papaya fruit and seed.

  3. The insect-proof enclosure which was proposed by the applicant to prevent dispersal of GM papaya pollen from the release site will have the additional advantage of preventing animals from accessing the release site. This will significantly limit the potential for GM papaya fruit or seeds to be dispersed, particularly as a licence condition requires that the enclosure is sealed at ground level. Additional licence conditions require the applicant to implement an accounting procedure for all fruit that are produced by the GM papaya trees and to monitor the insect-proof enclosure every day to ensure that its integrity is not compromised. If this occurred to the extent that immediate repairs could not be made, the applicant is required to remove and destroy all flowers and fruit to prevent the inadvertent dispersal of fruit and seed.

  4. The licence also requires the applicant to transport any GM material, including fruit and seeds for analyses, in accordance with OGTR transportation guidelines. These require that GMOs and GM materials must not be transported unless contained within a primary, sealed container that is packed in a secondary, unbreakable container. In combination, these measures would significantly limit the likelihood of spread in the environment.

Section 2.4 Persistence of the GM papayas at the release site

  1. Fruit will be harvested during the trial for analyses of physiological, nutritional and quality attributes. Although some of the fruits will be allowed to ripen on the trees, many will be harvested while still green and immature, to enable analysis of the fruit-ripening process at different stages of maturity. As fruit bare the seeds, this research objective will significantly limit the potential for seeds of the GM papayas to become incorporated into a soil seed bank within the trial site and, thereby, will limit the potential for persistence of the GMOs at the site. As noted above, however, the applicant is required to account for each fruit produced on each papaya tree planted in the insect-proof enclosure, to regularly monitor the development of such fruit and to prevent ripe papaya fruit from dropping to the ground. This accounting and monitoring procedure would further limit the potential for GM papaya seeds to persist at the release site.

  2. Although it is difficult to reproduce papaya vegetatively (e.g. by ‘cuttings’) the applicant is also required to destroy the GM papayas at the trial’s conclusion, by cutting the trees to ground level and spraying the stumps with an appropriate herbicide. This will limit the potential for persistence of the GM papayas at the site. Further, licence conditions require that all plant material derived from the felled trees and not required for further research is destroyed by incineration.

  3. In addition, post harvest monitoring of the release site is required as a condition of the licence to ensure that any papayas that may germinate or re-grow in the release area after the trial has concluded are destroyed before flowering and that the GM papayas are unable to persist in the environment.

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