Ethylene-insensitive tobacco lacks nonhost resistance against soil-borne fungi

Abstract

Enhanced ethylene production is an early response of plants to pathogen attack and has been associated with both resistance and susceptibility to disease. Tobacco plants were transformed with the mutant etr1-1 gene from Arabidopsis, conferring dominant ethylene insensitivity. Besides lacking known ethylene responses, these transformants (Tetr) did not slow growth when contacting neighboring plants, hardly expressed defense-related basic pathogenesis-related proteins, and developed spontaneous stem browning. Whereas hypersensitive resistance to tobacco mosaic virus was unimpaired, Tetr plants had lost nonhost resistance against normally nonpathogenic soil-borne fungi.

Figure 1

Northern blot analysis of Samsun NN tobacco and four primary transformants of etr1–1. Total RNA was isolated from healthy plants (H) and plants inoculated with TMV 3 days earlier (T). Total RNA was electrophoresed, blotted, and hybridized with etr1–1, PR-1a, and PR-1g probes.

Figure 2

Endogenous and AB-induced ethylene production of Samsun NN tobacco and four primary etr1–1 transformants. Relative ethylene levels are expressed as a percentage of endogenous ethylene production of Samsun NN plants. Insert shows an expanded view of the endogenous ethylene levels. A relative ethylene production rate of 1 corresponds to 0.12 nmol ethylene/g fresh weight per hr.

Figure 3

Transgenic P12 plants and Tetr18 plants of the same age grown at high density. Control plants develop a “crowding effect,” which is absent in the Tetr18 plants.

Figure 4

(A) Flowers of P12 plants (Right) and Tetr18 plants (Left) of comparable age. (B) Different stadia of flowering of control and Tetr18 plants. a, unripe but colored flower; b, open mature flower with ripe pollen; c, wilted flower. Data represent the average of 50 flowers.

Figure 5

(A) Primary etr1–1 transformant showing spontaneously developed disease symptoms. (B) Control P12 plant (Left) and Tetr18 plant (Right) 11 days after inoculation with Pythium sylvaticum Campbell and Hendrix.