Highlights of the mini-symposium on extracellular vesicles in inter-organismal communication, held in Munich, Germany, August 2018.

All living organisms secrete molecules for intercellular communication. Recent research has revealed that extracellular vesicles (EVs) play an important role in inter-organismal cell-to-cell communication by transporting diverse messenger molecules, including RNA, DNA, lipids and proteins. These discoveries have raised fundamental questions regarding EV biology. How are EVs biosynthesized and loaded with messenger/cargo molecules? How are EVs secreted into the extracellular matrix? What are the EV uptake mechanisms of recipient cells? As EVs are produced by all kind of organisms, from unicellular bacteria and protists, filamentous fungi and oomycetes, to complex multicellular life forms such as plants and animals, basic research in diverse model systems is urgently needed to shed light on the multifaceted biology of EVs and their role in inter-organismal communications. To help catalyse progress in this emerging field, a mini-symposium was held in Munich, Germany in August 2018. This report highlights recent progress and major questions being pursued across a very diverse group of model systems, all united by the question of how EVs contribute to inter-organismal communication.

Five Reasons to Consider Phytophthora infestans a Reemerging Pathogen.

Phytophthora infestans has been a named pathogen for well over 150 years and yet it continues to "emerge", with thousands of articles published each year on it and the late blight disease that it causes. This review explores five attributes of this oomycete pathogen that maintain this constant attention. First, the historical tragedy associated with this disease (Irish potato famine) causes many people to be fascinated with the pathogen. Current technology now enables investigators to answer some questions of historical significance. Second, the devastation caused by the pathogen continues to appear in surprising new locations or with surprising new intensity. Third, populations of P. infestans worldwide are in flux, with changes that have major implications to disease management. Fourth, the genomics revolution has enabled investigators to make tremendous progress in terms of understanding the molecular biology (especially the pathogenicity) of P. infestans. Fifth, there remain many compelling unanswered questions.

Novel quorum-sensing-controlled genes in Erwinia carotovora subsp. carotovora: identification of a fungal elicitor homologue in a soft-rotting bacterium.

Seven new genes controlled by the quorum-sensing signal molecule N-(3-oxohexanoyl)-L-homoserine lactone (OHHL) have been identified in Erwinia carotovora subsp. carotovora. Using TnphoA as a mutagen, we enriched for mutants defective in proteins that could play a role in the interaction between E. carotovora subsp. carotovora and its plant hosts, and identified NipEcc and its counterpart in E. carotovora subsp. atroseptica. These are members of a growing family of proteins related to Nep1 from Fusarium oxysporum which can induce necrotic responses in a variety of dicotyledonous plants. NipEcc produced necrosis in tobacco, NipEca affected potato stem rot, and both affected virulence in potato tubers. In E. carotovora subsp. carotovora, nip was shown to be subject to weak repression by the LuxR family regulator, EccR, and may be regulated by the negative global regulator RsmA.

Genome sequence of the enterobacterial phytopathogen Erwinia carotovora subsp. atroseptica and characterization of virulence factors.

The bacterial family Enterobacteriaceae is notable for its well studied human pathogens, including Salmonella, Yersinia, Shigella, and Escherichia spp. However, it also contains several plant pathogens. We report the genome sequence of a plant pathogenic enterobacterium, Erwinia carotovora subsp. atroseptica (Eca) strain SCRI1043, the causative agent of soft rot and blackleg potato diseases. Approximately 33% of Eca genes are not shared with sequenced enterobacterial human pathogens, including some predicted to facilitate unexpected metabolic traits, such as nitrogen fixation and opine catabolism. This proportion of genes also contains an overrepresentation of pathogenicity determinants, including possible horizontally acquired gene clusters for putative type IV secretion and polyketide phytotoxin synthesis. To investigate whether these gene clusters play a role in the disease process, an arrayed set of insertional mutants was generated, and mutations were identified. Plant bioassays showed that these mutants were significantly reduced in virulence, demonstrating both the presence of novel pathogenicity determinants in Eca, and the impact of functional genomics in expanding our understanding of phytopathogenicity in the Enterobacteriaceae.