Internalization of Flax Rust Avirulence Proteins into Flax and Tobacco Cells Can Occur in the Absence of the Pathogen

Author:

Rafiqi Maryam1,Gan Pamela H.P.1,Ravensdale Michael2,Lawrence Gregory J.2,Ellis Jeffrey G.2,Jones David A.1,Hardham Adrienne R.1,Dodds Peter N.2

Affiliation:

1. Division of Plant Science, Research School of Biology, College of Medicine, Biology, and Environment, Australian National University, Canberra, Australian Capital Territory 0200, Australia

2. CSIRO Plant Industry, Canberra, Australian Capital Territory 2601, Australia

Abstract

Abstract Translocation of pathogen effector proteins into the host cell cytoplasm is a key determinant for the pathogenicity of many bacterial and oomycete plant pathogens. A number of secreted fungal avirulence (Avr) proteins are also inferred to be delivered into host cells, based on their intracellular recognition by host resistance proteins, including those of flax rust (Melampsora lini). Here, we show by immunolocalization that the flax rust AvrM protein is secreted from haustoria during infection and accumulates in the haustorial wall. Five days after inoculation, the AvrM protein was also detected within the cytoplasm of a proportion of plant cells containing haustoria, confirming its delivery into host cells during infection. Transient expression of secreted AvrL567 and AvrM proteins fused to cerulean fluorescent protein in tobacco (Nicotiana tabacum) and flax cells resulted in intracellular accumulation of the fusion proteins. The rust Avr protein signal peptides were functional in plants and efficiently directed fused cerulean into the secretory pathway. Thus, these secreted effectors are internalized into the plant cell cytosol in the absence of the pathogen, suggesting that they do not require a pathogen-encoded transport mechanism. Uptake of these proteins is dependent on signals in their N-terminal regions, but the primary sequence features of these uptake regions are not conserved between different rust effectors.

Publisher

Oxford University Press (OUP)

Subject

Cell Biology,Plant Science

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