Agroinfiltration Is a Versatile Tool That Facilitates Comparative Analyses of Avr9/Cf-9-Induced and Avr4/Cf-4-Induced Necrosis

摘要

The avirulence genes Avr 9 and Avr 4 from the fungal tomato pathogen Cladosporium fulvum encode extracellular proteins that elicit a hypersensitive response when injected into leaves of tomato plants carrying the matching resistance genes, Cf-9 and Cf-4 , respectively. We successfully expressed both Avr 9 and Avr 4 genes in tobacco with the Agrobacterium tumefaciens transient transformation assay (agroinfiltration). In addition, we expressed the matching resistance genes, Cf-9 and Cf-4 , through agroinfiltration. By combining transient Cf gene expression with either transgenic plants expressing one of the gene partners, Potato virus X (PVX)-mediated Avr gene expression, or elicitor injections, we demonstrated that agroinfiltration is a reliable and versatile tool to study Avr/Cf -mediated recognition. Significantly, agroinfiltration can be used to quantify and compare Avr/Cf -induced responses. Comparison of different Avr/Cf -interactions within one tobacco leaf showed that Avr 9/ Cf-9 -induced necrosis developed slower than necrosis induced by Avr 4/ Cf-4 . Quantitative analysis demonstrated that this temporal difference was due to a difference in Avr gene activities. Transient expression of matching Avr/Cf gene pairs in a number of plant families indicated that the signal transduction pathway required for Avr/Cf -induced responses is conserved within solana-ceous species. Most non-solanaceous species did not develop specific Avr/Cf -induced responses. However, co-expression of the Avr 4/ Cf-4 gene pair in lettuce resulted in necrosis, providing the first proof that a resistance ( R ) gene can function in a different plant family.