Insect resistance trait

Inheritance of the Insect Resistance Trait. Copy numbers or the T-DNA inserts in transgenic plants were determined using Southern blotting. Plants expressing highest levels of B.t. protein contained around 5 copies of T-DNA. From one such plant, 15 F1 progeny were assayed and they all exhibited 100% insect killing. 

The wild tomato, Lycopersicon pennellii, and the wild potato, Solanum berthaultiif are two species which exhibit insect resistance conferred by glandular trichomes. S, berthaultii and L. pennellii have been the focus of efforts at Cornell University to transfer trichome-based insect resistance traits. This chapter reviews our knowledge of the biochemistry of glandular trichome-based insect resistance in these species. 

KLIEBENSTEIN, D., PEDERSEN, D BARKER, B MITCHELL-OLDS, T Comparative analysis of quantitative trait loci controlling glucosinolates, myrosinase and insect resistance in Arabidopsis thaliana., Genetics, 2002,161,325-332. 

Another major application of herbicide resistance is its utility as a selectable marker. Like antibiotic resistance in bacterial transformation, herbicide resistance should prove extremely useful for selecting transformants that are insect resistant, disease resistant, or engineered for other non-selectable traits. Many of these herbicide resistant markers have already been integrated into plant cloning vectors (32.43). 

Kroymann, J., Donnerhacke, S., Schnabelrauch, D. and Mitchell-Olds, T. (2003) Evolutionary dynamics of an Arabidopsis insect resistance quantitative trait locus. Proc. Natl. Acad. Sci. USA, 100,14587-92. 

Zhang, Z.-Y., Ober, J.A. and Kliebenstein, D.J. (2006) The gene controlling the quantitative trait locus Epithiospecifier modifier 1 alters glucosinolate hydrolysis and insect resistance in Arabidopsis. Plant Cell, 18,1524—36. 

Studies of the potential costs associated with xenobiotic resistance in the absence of the selective agent can suffer from several confounding experimental factors. First, fitness costs associated with strains in which resistance has been repeatedly selected for in the laboratory are unlikely to represent fitness costs associated with resistance mechanisms found in the field. Second, the resistant and susceptible strains compared are also often genetically unrelated and any observed costs may therefore be independent of the resistance trait itself Third, when insects are used they are often not checked for the presence of microbial pathogens, such as Wolhachia, which can influence the outcome of crosses between infected and uninfected strains. 

The main traits with which GM crops have been modified are herbicide resistance and insect resistance [1]. Herbicide resistance allows for the topical application of broad-spectrum herbicides, such as glyphosate and glufosinate, which would otherwise be detrimental to the crop. Insect resistance has in most cases been achieved by the introduction of insecticidal proteins that naturally occur in the soil bacterium Bacillus thuringiensis, which is also used as a biological pesticide in agriculture, in particular in organic agriculture. 

There are three commercially available herbicide resistant traits in cotton glyphosate resistance (Roundup Ready , RR), glufosinate resistance (Liberty Link , LL), and bromoxynil resistance (BXN ). In 2005, herbicide resistance traits were cultivated on over 80% of approximately 14 million total cotton acres in the United States (Fig. 6.1.3) [6]. This acreage represents a combination of herbicide resistance alone or stacked with other traits such as insect control traits. 

We have been involved in mechanistic studies aimed at understanding the basis of glandular trichome-based insect resistance in wild Solarium (potato) and Lycopersicon (tomato) species. Much effort has focused on identification of wild members of the Solanaceae with potentially useful resistance traits for introgression into Solarium tuberosum and Lycopersicon esculentum. In many cases resistance has been shown to be conferred by glandular trichomes, modified epidermal cells (i) which function as physical and/or chemical barriers against insect attack (2-10 > Tingey, this volume). 

Numerous plant alkaloids with antiherbivore properties are classified according to their mode of action (e.g., toxins, antifeedants, antidigestive proteins, etc.) and have been used in agriculture to control insect pests. The pyridine alkaloid nicotine is one of the best-studied putative plant resistance traits. Because it can interact with the acetylcholine receptors in the nervous systems of animals, nicotine is extremely toxic to most herbivores and, consequently, was one of the first insecticides used to control pests in agriculture. Evidence for the resistance value of nicotine arises from... 

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