The TASTY Locus on Chromosome 1 of Arabidopsis Affects Feeding of the Insect Herbivore Trichoplusia ni  

Abstract

The generalist insect herbivore Trichoplusia ni(cabbage looper) readily consumes Arabidopsis and can complete its entire life cycle on this plant. Natural isolates (ecotypes) of Arabidopsis are not equally susceptible to T. ni feeding. While some are hardly touched by T. ni, others are eaten completely to the ground. Comparison of two commonly studied Arabidopsis ecotypes in choice experiments showed that Columbia is considerably more resistant than Landsberg erecta. In no-choice experiments, where larvae were confined on one or the other ecotype, weight gain was more rapid on Landsberg erectathan on Columbia. Genetic mapping of this difference in insect susceptibility using recombinant inbred lines resulted in the discovery of the TASTY locus near 85 cM on chromosome 1 of Arabidopsis. The resistant allele of this locus is in the Columbia ecotype, and an F1 hybrid has a sensitive phenotype that is similar to that of Landsberg erecta. TheTASTY locus is distinct from known genetic differences between Columbia and Landsberg erecta that affect glucosinolate content, trichome density, disease resistance, and flowering time.

Variations in CYP74B2 (Hydroperoxide Lyase) Gene Expression Differentially Affect Hexenal Signaling in the Columbia and Landsberg erecta Ecotypes of Arabidopsis

“…The contrasting higher transcript levels in the Col ecotype (2.3-fold) of CYP83B1, which mediates synthesis of indole glucosinolates Hansen et al, 2001), suggests that compensatory interplay exists between the CYP83A1 and CYP83B1 loci as previously seen in the studies of Hemm et al (2003) and Naur et al (2003). The differential expression of CYP83A1 in these ecotypes partially explains the different basal glucosinolate profiles in the Col and Ler ecotypes (Kliebenstein et al, 2001a) and the higher overall glucosinolate content of the Ler ecotype (Jander et al, 2001). Presumably these different basal levels of glucosinolates contribute to variations in ecotype resistance to insect predators as myrosinases release toxic glucosinolate derivatives (Rask et al, 2000).…”

“…Considerable variation that, in fact, exists at the DNA sequence level results in an extensive range of phenotypic variations between these ecotypes in biochemical and morphological characteristics associated with defense responses. Examples of this variation include differences in disease resistance (Kunkel, 1996), leaf trichome density (Larkin et al, 1996), glucosinolate content (Kliebenstein et al, 2001a;Raybould and Moyes, 2001), epicuticular wax composition (Rashotte et al, 1997), and insect resistance (Jander et al, 2001). While complicating molecular analysis of this plant species, these natural variations have provided an imported genetic resource for analyzing gene functions.…”

Genotype, Age, Tissue, and Environment Regulate the Structural Outcome of Glucosinolate Activation

“…However, the ecological roles of many of these defensive metabolites remain undefined, requiring further experiments to understand the ecological significance of these results. In particular, the biological role of simple nitrile activation products remains unclear, as simple nitrile structures are generally less toxic and provide less effective defense against polyphagous herbivores when compared directly with the corresponding isothiocyanates (Nastruzzi et al, 2000;Jander et al, 2001;Lambrix et al, 2001;Barth and Jander, 2006;Zhang et al, 2006). We hypothesize that increased proportions of simple nitrile and epithionitrile products reduce the risk of detection by adapted herbivores or provide indirect defense by attracting predators and parasites of adapted herbivores.…”

A Conserved Transcript Pattern in Response to a Specialist and a Generalist Herbivorew⃞

“…Indole glucosinolates have a core structure comprising a b-D-thioglucose group linked to a sulfonated aldoxime moiety and a Trp side chain. These compounds are thought to be part of a constitutive defense mechanism (Jander et al, 2001;Lambrix et al, 2001), but levels of specific indole glucosinolates can also increase upon elicitor, MeJA, or salicylic acid (SA) treatment (Doughty et al, 1995;Brader et al, 2001;Mikkelsen et al, 2003). Several genes involved in the biosynthesis of indole glucosinolates were shown to be transcriptionally regulated by MeJA (Brader et al, 2001;Mikkelsen et al, 2003).…”