PT - JOURNAL ARTICLE AU - Benjamin Petre AU - Michaela Kopischke AU - Alexandre Evrard AU - Silke Robatzek AU - Sophien Kamoun TI - Cell re-entry assays do not support models of pathogen-independent translocation of AvrM and AVR3a effectors into plant cells AID - 10.1101/038232 DP - 2016 Jan 01 TA - bioRxiv PG - 038232 4099 - http://biorxiv.org/content/early/2016/01/29/038232.short 4100 - http://biorxiv.org/content/early/2016/01/29/038232.full AB - The cell re-entry assay is widely used to evaluate pathogen effector protein uptake into plant cells. The assay is based on the premise that effector proteins secreted out of a leaf cell would translocate back into the cytosol of the same cell via a yet unknown host-derived uptake mechanism. Here, we critically assess this assay by expressing domains of the effector proteins AvrM-A of Melampsora lini and AVR3a of Phytophthora infestans fused to a signal peptide and fluorescent proteins in Nicotiana benthamiana. We found that the secreted fusion proteins do not re-enter plant cells from the apoplast and that the assay is prone to false-positives. We therefore emit a cautionary note on the use of the cell re-entry assay for protein trafficking studies.