Chitinolytic transgenes from Streptomyces albidoflavus as phytochemicals defences against herbivorous insects, use in transgenic plants and effect in plant development

Chitinolytic enzymes are proteins that catalyze the hydrolysis of chitin. Chitin is the principal component of the insect cuticle. It has been hypothesized that ingestion of chitinolytic enzymes from Streptomyces albidoflavus, have the potential to increase resistance to insects when transgenically introduced in plants. In order to demonstrate this hypothesis, a series of studies were performed.; The initial study evaluated the effect of artificial diets supplemented with a mixture of chitinolytic enzymes from S. albidoflavus on Hypothenemus hampei (Ferrari) (Coleoptera: Scolytidae), Trichoplusia ni (Hubner), and Helicoverpa virescens (Fabricius) (Iepidoptera: Noctuidae). These experiments demonstrate that the chitinolytic enzymes inhibit growth and development of the three species of insects, and caused mortality in H. hampei.; Next, three constructs were assembled: (I) pS.a endochitinase, which expresses the endochitinase gene, (II) p S.a-chitobiosidase, which expresses the chitobiosidase gene, and (III) pS.a endochitinase-chitobiosidase, which expresses both genes in tandem.; Transgenic plants were produced using these transformation vectors. Agrobacterium tumefaciens was used for transformation of tobacco (Nicotiana tabacum), tomato (Lycopersicon esculentum ) and ‘Marshall McIntosh’ apple (Malux-domestica Borkh). In addition, transformation of coffee cultivar Colombia (Coffea arabica var. caturra-Timor hybrid) was accomplished by particle bombardment.; Then, the effect of the transgenic plants on the insects was determined. The result of these bioassays showed that chitinase genes from S. albidoflavus expressed in tomato enhanced resistance to T. ni, causing mortality and reducing the growth and development of the insects. In addition studies of the effect of the ingestion of transgenic tomato in the peritrophic membranes of T. ni were performed, which indicated that the chitinolytic enzymes altered the permeability of the peritrophic, membrane. Those genes expressed in apple plants enhanced resistance to Choristoneura rosaceana and Helicoverpa virescens by reducing the growth and development of the insects.; Tomato transgenic plants expressing higher levels of chitinolytic activity than the non-transgenic plants showed a significant reduction in height and displayed earlier flowering than the control plants. Chitinolytic enzymes have a role in the development of the tomato plants, and the endochitinase and chitobiosidase genes from S. albidoflavus can significantly reduce developmental time by speeding up the process of flowering and fruiting of tomato, and increase the number of fruits produced. These two genes are directly associated with plant productivity.