Plant diseases cause massive losses in agriculture. Increasing the natural defenses of plants may reduce the impact of phytopathogens on agricultural productivity. Pattern-recognition receptors (PRRs) detect microbes by recognizing conserved pathogen-associated molecular patterns (PAMPs). Although the overall importance of PAMP-triggered immunity for plant defense is established, it has not been used to confer disease resistance in crops. We report that activity of a PRR is retained after its transfer between two plant families. Expression of EFR (ref. 4), a PRR from the cruciferous plant Arabidopsis thaliana, confers responsiveness to bacterial elongation factor Tu in the solanaceous plants Nicotiana benthamiana and tomato (Solanum lycopersicum), making them more resistant to a range of phytopathogenic bacteria from different genera. Our results in controlled laboratory conditions suggest that heterologous expression of PAMP recognition systems could be used to engineer broad-spectrum disease resistance to important bacterial pathogens, potentially enabling more durable and sustainable resistance in the field.

Pathogens use specialized secretion systems and targeting signals to translocate effector proteins inside host cells, a process that is essential for promoting disease and parasitism. However, the amino acid sequences that determine host delivery of eukaryotic pathogen effectors remain mostly unknown. The Crinkler (CRN) proteins of oomycete plant pathogens, such as the Irish potato famine organism Phytophthora infestans, are modular proteins with predicted secretion signals and conserved N-terminal sequence motifs. Here, we provide direct evidence that CRN N termini mediate protein transport into plant cells. CRN host translocation requires a conserved motif that is present in all examined plant pathogenic oomycetes, including the phylogenetically divergent species Aphanomyces euteiches that does not form haustoria, specialized infection structures that have been implicated previously in delivery of effectors. Several distinct CRN C termini localized to plant nuclei and, in the case of CRN8, required nuclear accumulation to induce plant cell death. These results reveal a large family of ubiquitous oomycete effector proteins that target the host nucleus. Oomycetes appear to have acquired the ability to translocate effector proteins inside plant cells relatively early in their evolution and before the emergence of haustoria. Finally, this work further implicates the host nucleus as an important cellular compartment where the fate of plant-microbe interactions is determined.plant immunity | Phytophthora | Crinklers | translocation | nuclear localization P lant and animal pathogens target secreted proteins (cytoplasmic effectors) inside host cells where they directly modify or perturb host cellular processes (1-5). These pathogens use specialized secretion systems for effector delivery, a process that in most cases requires a specific targeting signal. In bacteria, several secretion systems are known, among which the type III secretion system is critical for pathogenicity of several Gram-negative plant pathogenic bacteria (6, 7). In filamentous pathogenic eukaryotes (fungi and oomycetes), the mechanisms and amino acid sequence signals that determine host translocation remain mostly unknown. An exception is the oomycete RXLR family of cytoplasmic effectors (8-10). RXLR effectors are defined by a conserved N-terminal motif similar in sequence, position, and function to a host translocation signal present in malaria parasites that enables delivery of effector proteins inside plant and human cells (11)(12)(13)(14). These effectors accumulate in specialized infection structures of Phytophthora, known as haustoria, before their delivery inside plant cells (14). Among the RXLR effectors, the Phytophthora infestans protein AVR3a is well studied and has been shown to confer avirulence on plants expressing the intracellular immune receptor R3a from potato (14-17).Species of the oomycete genus Phytophthora are arguably the most devastating pathogens of dicotyledonous plants and include notorious pathogens, such as P. infestans...

Little is known of how plant disease resistance (R) proteins recognize pathogens and activate plant defenses. Rcr3 is specifically required for the function of Cf-2, a Lycopersicon pimpinellifolium gene bred into cultivated tomato (Lycopersicon esculentum) for resistance to Cladosporium fulvum. Rcr3 encodes a secreted papain-like cysteine endoprotease. Genetic analysis shows Rcr3 is allelic to the L. pimpinellifolium Ne gene, which suppresses the Cf-2-dependent autonecrosis conditioned by its L. esculentum allele, ne (necrosis). Rcr3 alleles from these two species encode proteins that differ by only seven amino acids. Possible roles of Rcr3 in Cf-2-dependent defense and autonecrosis are discussed.