G. Honee et al., INDUCTION OF DEFENSE-RELATED RESPONSES IN CF9 TOMATO CELLS BY THE AVR9 ELICITOR PEPTIDE OF CLADOSPORIUM-FULVUM IS DEVELOPMENTALLY-REGULATED, Plant physiology, 117(3), 1998, pp. 809-820
The AVR9 elicitor from the fungal pathogen Cladosporium fulvum induces
defense-related responses, including cell death, specifically in toma
to (Lycopersicon esculentum Mill.) plants that carry the Cf-9 resistan
ce gene. To study biochemical mechanisms of resistance in detail, susp
ension cultures of tomato cells that carry the Cf-9 resistance gene we
re initiated. Treatment of cells with various elicitors, except AVR9,
induced an oxidative burst, ion fluxes, and expression of defense-rela
ted genes. Agrobacterium tumefaciens-mediated transformation of Cf9 to
mato leaf discs with Avr9-containing constructs resulted efficiently i
n transgenic callus formation. Although transgenic callus tissue showe
d normal regeneration capacity, transgenic plants expressing both the
Cf-9 and the Avr9 genes were never obtained. Transgenic F-1 seedlings
that were generated from crosses between tomato plants expressing the
Avr9 gene and wild-type Cf9 plants died within a few weeks. However, c
allus cultures that were initiated on cotyledons from these seedlings
could be maintained for at least 3 months and developed similarly to c
allus cultures that contained only the Cf-9 or the Avr9 gene. It is co
ncluded, therefore, that induction of defense responses in Cf9 tomato
cells by the AVR9 elicitor is developmentally regulated and is absent
in callus tissue and cell-suspension cultures, which consists of undif
ferentiated cells. These results are significant for the use of suspen
sion-cultured cells to investigate signal transduction cascades.