Subcellular localization of Phytophthora infestans RXLR effector AVR1 and its cognate resistance protein R1

Phytophthora infestans is a devastating plant pathogen that causes late blight on potato and tomato. To colonize host plants, P. infestans secretes effectors that can modulate host defence. Well-known are the RXLR effectors, which are able to translocate into host cells to manipulate the cell machinery. However, to counteract the pathogen potato has a set of immune receptors known as nucleotide-binding leucine-rich repeat (NLR) proteins that confer resistance against P. infestans. NLR-conferred resistance is mediated by recognition of RXLR effectors, with each NLR protein (or R protein) having its own cognate RXLR effector (or AVR protein). The mechanisms underlying NLR-mediated resistance are still poorly understood. In this study we focussed on the P. infestans RXLR effector AVR1 and its cognate potato NLR R1 and addressed the question in which subcellular compartment effector perception and defence activation takes place. We determined the subcellular localization of both AVR1 and R1. We also fused Nuclear Localization Signals (NLS) and Nuclear Export Signals (NES) to R1 and AVR1, as well as mutated NLS and NES, and used these constructs for artificial subcellular targeting of R1 and AVR1. This allowed us to determine the subcellular localization that is required to elicit R1-mediated immunity and AVR1-mediated host defence suppression.