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 erecta than 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 F(1) hybrid has a sensitive phenotype that is similar to that of Landsberg erecta. The TASTY locus is distinct from known genetic differences between Columbia and Landsberg erecta that affect glucosinolate content, trichome density, disease resistance, and flowering time.

Figure 1

Mean and sd of weight gain (dry weight) of newly hatched cabbage looper larvae feeding for 1 week on Col (n = 113) and Ler (n = 119) ecotypes in a no-choice experiment (P < 0.01, Student's t test).

Figure 2

Five-week-old plants of Col, Ler, and RI lines derived from these ecotypes were exposed to cabbage looper larvae for 3 d. Larvae were allowed to feed at will until they stopped feeding. The inflorescences and leaves of Col and RI line 214 are resistant to cabbage looper feeding, whereas Ler and RI line 184 are sensitive and are almost completely consumed.

Figure 3

LOD scores for cabbage looper feeding on RI lines derived from Col and Ler ecotypes relative to markers on the Arabidopsis genetic map. A locus between the markers Tag1 and p4 on chromosome I has a significant effect on cabbage looper feeding, with the resistant allele coming from the Col ecotype. The dashed line represents the 99% confidence threshold for this data set.

Figure 4

A, Total glucosinolate content of Col and Ler plants expressed as micromolar glucosinolates per gram of plant material. Bars show mean and sd of eight samples, P = 0.08 (Student's t test). B, Myrosinase activity in Col and Ler plants expressed as micromolar Glc released from sinigrin per minute per gram of plant material. Bars show mean and sd of eight samples, P = 0.01 (Student's t test).