Development of transgenic wheat (Triticum aestivum L.) expressing avidin gene conferring resistance to stored product insects

Wheat is an important staple crop in many countries. Depending on the climatic and
storage conditions, it can become infested by a wide variety of stored-product insect
pests 1]. Avidin-containing wheat and its processed products would be resistant to infestations
caused by all of the species. Detection and control methods for stored product insects
have to be through integrated pest management program (IPM). Major efforts involving
sanitation practices, exclusion techniques, habitat modifications, fumigation, and
insecticide applications are usually required to prevent damage. The conventional
insect control method is mainly dependent on the intensive and extensive use of chemical
pesticides, which have drawbacks such as doing harm to the ecological system, producing
residual poisons to human beings and animals, and high cost. Moreover, some insects
have developed resistance to some of the available insecticides 32],33]. Therefore, it is desirable to develop insect-resistant plants through the introduction
of insect-resistant genes (e.g. avidin) through genetic transformation. In present
study, synthetic avidin coding DNA was transferred to wheat plants. Avidin accumulation
was detected in transgenic plants by ELISA and western dot blot. We found that avidin
wheat has excellent resistance to storage insects. Bioassay experiments proved that
insect mortality in the first week was about 30 %, in second week it was about 70 %
and in the third week the mortality was 100 %. Similar results were obtained with
the red flour beetle Tribolium confusum, and flat grain beetle Cryptolestes pusillus19]. Avidin transgenic tobacco halted growth and it caused mortality in larvae of two
lepidopterans, Helicoverpa armigera and Spodoptera litura. The insects showed very poor growth over their first 8 days on a diet consisting
of the leaves from transgenic plants and significant mortality were reported after
11 or 12 days and all insects were dead after 22 days 34]. In conclusion, the stable avidin transgenic wheat showed high level of resistance
to the stored product insect (Sitophilus granarius). This study will hopefully decrease the loss of wheat seeds in warehouses significantly.
In addition, the avidin-transgenic wheat powder can be used as a bioinsecticide. Avidin
may interfere with enzymes that depend on enzyme bound biotin, such as those involved
in carboxylation, decarboxylation, and transcarboxylation reactions 35]. Biotin deficiency in the blowfly, Aldrichina grahami, caused decreases in several fatty acids 36]. Presumably, a similar biochemical effect led to the stunted growth and mortality
of the stored-product insects studied here. The public acceptability of avidin wheat
as a food or feed is difficult to predict. Careful examination of its safety, however,
is needed before consumption by humans and livestock can be considered. Kramer et
al., 19] reported that at least there is no acute toxicity of avidin when feed to mice. Long-term
ingestion of high levels of avidin maize may be a problem, because a biotin deficiency
can decrease the growth rate of mice and affect reproduction 36],37]. However, avidin is a food protein that is consumed in the form of egg at a concentration
of 400 part per million (ppm) by dry weight, which is four times higher than its
concentration in most of the wheat used in the present study. Moreover, avidin has
an antidote (biotin), which can be used to prevent toxicity or to rescue potential
victims from adverse effects. Food and feed uses of avidin wheat might involve processing
that includes supplementation with the vitamins. Another method that would help to
prevent potential toxicity of the avidin wheat is the heat treatment, which would
denature most of the avidin as well as the avidin–biotin complex and release most
of the vitamins 38]–40]. Currently development of wheat expressing transgenic avidin as a food or feed grain
could be considered after thorough risk assessment. In addition to its efficacy against
postharvest insect pests, avidin also is effective against preharvest pests such as
the beet armyworm, black cutworm, bollworm, and other species for which biotin is
an essential growth factor 41],42]. Transferring the avidin gene to other crops will be important in determining its
potential usefulness in a variety of other commercial protein production and pest
control situations. Risk assessment of these transgenics can be done following the
National Biosafety Committee guidelines for the most efficient avidin-transgenic line.
In addition, different species of stored cereals insects can be challenged with the
avidin transgenic wheat grains and flour.