Characterization of Elicitor-Induced Defense Responses in Suspension-Cultured Cells ofArabidopsis

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Abstract
When suspension-cultured cells of Arabidopsis (ecotype Fi-3) were treated with crude preparations of the bacterial [Erwinia carotovora pv. carotovora] pectin-degrading enzyme .alpha.-1,4-endopolygalacturonic acid lyase (PGA lyase), they expressed a number of putative defense responses including increased levels of several enzymes involved in phenylpropanoid biosynthesis. Phenylalanine ammonia-lyase (PAL) and 4-coumarate: CoA ligase (4CL) were transiently induced with similar induction kinetics cell wall components from Phytophthora magasperma f. sp. glycinea (Pmg elicitor) and reached maximum levels at 8 to 10 hr after elicitor treatment. Caffeic acid O-methyl transferase (CMT) and peroxidase had induction kinetics distinct from those observed for PAL and 4CL; maximum levels of these two enzymes were observed approximately 24 hr after elicitor treatment and were maintained for at least 48 hr. The transient increases in PAL and 4CL enzyme activities were preceded by transient increases in the steady-state levels of their mRNAs, which peaked approximately 3 hr after elicitor treatment. Cell cultures treated with PGA lyase also had increased steady-state levels of mRNAs of .beta.-1,3-glucanase, another putative plant defense response. These results demonstrate that the overall response of Arabidopsis cells to elicitor treatment is very similar to that observed in other cell culure systems and provides the first indication as to the nature of some of the defense responses elaborated by Arabidopsis. This is an important first step developing Arabidopsis as a model system for studying plant-pathogen interactions.

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