Gene transfer

Patented

Comments

I. Substances occurring in plants

1. Sugar (glucosinolates polysaccharides)

No

No

The relative concentration of different sugars determines whether or not certain insects prefer a given plant or species (saccarose is preferred; not used in breeding

2. Terpenoids

No

No

Large group of substances including pyrethrin I, sesquiterpenoid and phytoecdysteroids. Some terpenoids are common in cotton

3. Alkaloids and glycoalkaloids

No

No

Includes nicotine, which has long been used as biological pesticide produced from tobacco extracts. Also used in classical breeding such as in potato (demissin and (α-tomatin). Several Brassica species also contain sulfides (glycoside) which are toxic to some insects and attract other.

4. Flavanoids

No

No

-

5. Phenols

No

No

Overexpresion of polyphenoloxydase leading to increase production of quinonin which is toxic for insects. Unlikely to be used I genetic engineering due to complex chemistry and possible toxicity to mammals

6. Protein antimetabolites

All are secondary metabolites

6.1 Amino acids and primary storage proteins

No

No

e.g. in wheat, gluten proteins are not digestible by some insects (Eurygaster integriceps) and thus confer partial resistance against insects. The presence of certain aminoacids generally increases resistance in rice.

6.2 Lectins inhibitors (also referred to as plant peptide hormones)

Yes

Yes

Lectins are common in the grains of cereals, particularly during germination. Certain lectins also have antifungal properties. Much work is going on with the snowdrop lectin (GNA); particularly promising for sucking insects (Homoptera), which cannot be controlled with Bt.

6.3 Protease inhibitors (includes trypsin and chymotrysin inhibitors)

Yes

Yes

Act on exogenous proteolytic enzymes. Trypsin inhibitor has particularly broad insect spectrum and has been demonstrated to be synergistic with Bt; much work is being done with the cowpea protease inhibitors (CpTI).

6.4 α-amylase inhibitors

Yes

yes

Widely occurring in seeds particularly dicots. For gene transfer, the most effective so far has been the α-amylase inhibitors genes from the common bean.

II. Substance not occurring in plants

Yes

Yes

See text for details

Yes

yes

e.g. isopentenyl transferase (ipt gene) which affects the Cytokinin biosynthesis in insects, leading to increased levels of toxins in insects. Such genes from bacteria have been transferred to several crops.

9. Other toxins

Yes

Yes

e.g. spider and wasp toxins have been transferred to plants for experimental purposed. Unlikely to be applied in crops due to effect of some toxins on mammals.

10. Smart proteins

Yes

Yes

Computer aided design of novel proteins