Probing formation of cargo/importin-α transport complexes in plant cells using a pathogen effector

Wirthmueller, Lennart, Roth, Charlotte, Fabro, Georgina, Caillaud, Marie-Cécile, Rallapalli, Ghanasyam, Asai, Shuta, Sklenar, Jan, Jones, Alexandra M. E., Wiermer, Marcel, Jones, Jonathan D. G. and Banfield, Mark J. (2015) Probing formation of cargo/importin-α transport complexes in plant cells using a pathogen effector. The Plant Journal, 81 (1). pp. 40-52. ISSN 0960-7412

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Importin-αs are essential adapter proteins that recruit cytoplasmic proteins destined for active nuclear import to the nuclear transport machinery. Cargo proteins interact with the importin-α armadillo repeat domain via nuclear localization sequences (NLSs), short amino acids motifs enriched in Lys and Arg residues. Plant genomes typically encode several importin-α paralogs that can have both specific and partially redundant functions. Although some cargos are preferentially imported by a distinct importin-α it remains unknown how this specificity is generated and to what extent cargos compete for binding to nuclear transport receptors. Here we report that the effector protein HaRxL106 from the oomycete pathogen Hyaloperonospora arabidopsidis co-opts the host cell's nuclear import machinery. We use HaRxL106 as a probe to determine redundant and specific functions of importin-α paralogs from Arabidopsis thaliana. A crystal structure of the importin-α3/MOS6 armadillo repeat domain suggests that five of the six Arabidopsis importin-αs expressed in rosette leaves have an almost identical NLS-binding site. Comparison of the importin-α binding affinities of HaRxL106 and other cargos in vitro and in plant cells suggests that relatively small affinity differences in vitro affect the rate of transport complex formation in vivo. Our results suggest that cargo affinity for importin-α, sequence variation at the importin-α NLS-binding sites and tissue-specific expression levels of importin-αs determine formation of cargo/importin-α transport complexes in plant cells.

Item Type: Article
Additional Information: © 2014 The Authors The Plant Journal published by Society for Experimental Biology and John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Uncontrolled Keywords: importin-α,nucleo-cytoplasmic transport,nuclear localization sequence,oomycete effector,plant innate immunity,hyaloperonospora arabidopsidis,arabidopsis thaliana
Faculty \ School: Faculty of Science > The Sainsbury Laboratory
Faculty of Medicine and Health Sciences > Norwich Medical School
Faculty of Science > School of Biological Sciences
UEA Research Groups: Faculty of Science > Research Groups > Plant Sciences
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Depositing User: Pure Connector
Date Deposited: 09 Nov 2016 14:00
Last Modified: 22 Oct 2022 01:52
DOI: 10.1111/tpj.12691

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