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.

Effector biology of plant-associated organisms: concepts and perspectives.

Every plant is closely associated with a variety of living organisms. Therefore, deciphering how plants interact with mutualistic and parasitic organisms is essential for a comprehensive understanding of the biology of plants. The field of plant-biotic interactions has recently coalesced around an integrated model. Major classes of molecular players both from plants and their associated organisms have been revealed. These include cell surface and intracellular immune receptors of plants as well as apoplastic and host-cell-translocated (cytoplasmic) effectors of the invading organism. This article focuses on effectors, molecules secreted by plant-associated organisms that alter plant processes. Effectors have emerged as a central class of molecules in our integrated view of plant-microbe interactions. Their study has significantly contributed to advancing our knowledge of plant hormones, plant development, plant receptors, and epigenetics. Many pathogen effectors are extraordinary examples of biological innovation; they include some of the most remarkable proteins known to function inside plant cells. Here, we review some of the key concepts that have emerged from the study of the effectors of plant-associated organisms. In particular, we focus on how effectors function in plant tissues and discuss future perspectives in the field of effector biology.

A new member of the Arabidopsis WRKY transcription factor family, AtWRKY6, is associated with both senescence- and defence-related processes.

WRKY proteins constitute a large family of plant-specific transcription factors whose precise functions have yet to be elucidated. Here we show that expression of one representative in Arabidopsis, AtWRKY6, is influenced by several external and internal signals often involved in triggering senescence processes and plant defence responses. Progressive 5' deletions of the AtWRKY6 promoter allowed separation of defined regions responsible for the expression in distinct organs or upon pathogen challenge. Nuclear localization of AtWRKY6 was demonstrated; protein truncations and gain-of-function studies enabled delineation of a region harbouring a novel type of functional nuclear localization signal (NLS).

The WRKY superfamily of plant transcription factors.

The WRKY proteins are a superfamily of transcription factors with up to 100 representatives in Arabidopsis. Family members appear to be involved in the regulation of various physio-logical programs that are unique to plants, including pathogen defense, senescence and trichome development. In spite of the strong conservation of their DNA-binding domain, the overall structures of WRKY proteins are highly divergent and can be categorized into distinct groups, which might reflect their different functions.

Cloning and expression of a gibberellin 2 beta,3 beta-hydroxylase cDNA from pumpkin endosperm.

A cDNA expression library in lambda MOSEIox derived from poly(A)+ RNA from pumpkin endosperm was screened immunologically with a polyclonal antibody raised against partially purified gibberellin (GA) 2 beta,3 beta-hydroxylase from pumpkin endosperm. A recombinant fusion protein encoded by a selected positive clone catalyzed 3 beta-hydroxylation of GA15, GA24, GA25, and GA17 and of GA12-aldehyde, GA12, GA9, and GA20, albeit less efficiently. The fusion protein also catalyzed 2 beta-hydroxylation of the C20 GAS GA25, GA13, and, as identified putatively, GA28. The full-length clone contains an open reading frame of 1041 nucleotides encoding 346 amino acid residues with a predicted molecular weight of 38,992 and pI of 7.2. Transcript levels of this gene and of the previously cloned GA 7-oxidase and 20-oxidase genes from pumpkin endosperm rose until day 2 after the start of imbibition of the mature seeds, but only at one-two hundredth to one-six thousandth of the level found in the endosperm, as determined by quantitative reverse transcriptase-polymerase chain reaction. In contrast, GA 7-oxidase, 20-oxidase, and 3 beta-hydroxylase enzyme activities were present in cell-free systems prepared from embryos of mature seeds and decreased after imbibition.