Die Bedeutung von Myo5 für das polare Wachstum, die pathogene Entwicklung und den Transport polarer Chitinsynthasen in Ustilago maydis

Der phytopathogene Pilz Ustilago maydis ist der Erreger des Maisbeulenbrandes. Die Bildung des infektiösen dikaryotischen Filaments setzt die Fusion zweier kompatibler Sporidien voraus, die stimuliert durch das Pheromon des Partners Konjugationshyphen ausbilden, aufeinander zu wachsen und miteinander fusionieren. Sowohl für den Kreuzungsprozess als auch für die erfolgreiche Infektion der Wirtspflanze ist die Fähigkeit des Pilzes, polar zu wachsen, von essentieller Bedeutung. Polares Wachstum erfordert die gerichtete Anlieferung von Wachstums- und Zellwandkomponenten entlang des Cytoskeletts zur Wachstumsspitze hin. In der vorliegenden Arbeit konnte gezeigt werden, dass das Klasse V Myosin, Myo5, für verschiedene Stadien des Pilzes während seines sexuellen Lebenszyklus von enormer Bedeutung ist. Myo5 ist essentiell für die erfolgreiche Perzeption des Pheromons und die Ausbildung von Konjugationshyphen. Auch das Wachstum dikaryotischer Hyphen ist in myo5ts-Mutanten gestört. Zudem zeigten myo5ts-Infektionshyphen deutliche Störungen des polaren Wachstums während der frühen Infektionsphase, was sich in der Ausbildung geschwollene Hyphenverzweigungen äußerte, und sie induzierten bereits bei permissiver Temperatur nur bei 2,7% der Pflanzen Tumore. Aufgrund der aus Vorversuchen resultierenden Erkenntnisse wurden Chitinsynthasen als mögliche ?Cargos? von Myo5 in Betracht gezogen und näher untersucht. Das Genom von U. maydis kodiert für sieben Chitinsynthasen (Chs1-7) und eine Myosin-Chitinsynthase (Mcs1). Sowohl die Phänotypen der Chitinsynthase-Deletionsstämme wurden näher analysiert, als auch in vivo Lokalisationsstudien der Chitinsynthasen durchgeführt. Dabei zeigte sich, dass Dchs5- und auch Dchs7-Zellen ähnliche Zelltrennungsdefekte wie Dmyo5-Zellen sowie Störungen in der Ausbildung von Konjugationshyphen aufwiesen. Zudem führte die Deletion von chs7 zu einer starken Beeinträchtigung der Filamentbildung auf aktivkohlehaltigem Medium und der Pathogenität. Die Deletion von chs6 und mcs1 störte die Filamentbildung kompatibler Stämme nicht, resultierte allerdings in einer völligen Apathogenität. Ähnlich wie Myo5 lokalisierten die vier Chitinsynthasen Chs5, Chs6, Chs7 und Mcs1 in der Spitze wachsender Sporidien. Inhibitorversuche ergaben, dass die Lokalisation dieser polaren Chitinsynthasen von Aktin abhängt. Untersuchungen zur Lokalisation von Chs5, Chs6, Chs7 und Mcs1 in myo5ts-Mutanten zeigten eine deutliche Fehlverteilung von Chs7 in myo5ts-Mutanten nach einstündiger Inkubation bei restriktiver Temperatur. Durch den neu etabliertem in vivo Aktinmarker Fim1GFP konnte eine Störung des Aktin-Cytoskeletts als Ursache ausgeschlossen werden. Sowohl die phänotypischen Analysen als auch die Lokalisations- und Inhibitorstudien weisen deutlich auf eine Beteiligung von Myo5 an der Lokalisation von Chs7 hin

Interfaces between bacterial and eukaryotic "neuroecology"

The sensory capacity of bacteria and macroalgae (seaweeds) is limited with respect to many modalities (visual, auditory) common in "higher" organisms such as animals. Thus, we expect that other modalities, such as chemical signaling and sensing, would play particularly important roles in their sensory ecology. Here, we discuss two examples of chemical signaling in bacteria and seaweeds: (1) the role of chemical defenses and quorum-sensing (QS) regulatory systems in bacterial colonization and infection of the red alga Delisea pulchra and their ecological consequences, and (2) the regulation of dispersal and differentiation by nitric oxide (NO) in bacterial biofilms. Consistent with the goals of neuroecology, in both cases, we investigate the links between specific signal-mediated molecular mechanisms, and ecological outcomes, for populations or assemblages of bacteria or seaweeds. We conclude by suggesting that because of the fundamental role played by chemical signaling in bacteria, bacterial systems, either by themselves or in interactions with other organisms, have much to offer for understanding general issues in neuroecology. Thus, further integration of microbiology with the biology of eukaryotes would seem warranted and is likely to prove illuminating. © The Author 2011. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. All rights reserved

Reduced performance of native infauna following recruitment to a habitat-forming invasive marine alga

Despite well-documented negative impacts of invasive species on native biota, evidence for the facilitation of native organisms, particularly by habitat-forming invasive species, is increasing. However, most of these studies are conducted at the population or community level, and we know little about the individual fitness consequences of recruitment to habitat-forming invasive species and, consequently, whether recruitment to these habitats is adaptive. We determined the consequences of recruitment to the invasive green alga Caulerpa taxifolia on the native soft-sediment bivalve Anadara trapezia and nearby unvegetated sediment. Initially, we documented the growth and survivorship of A. trapezia following a natural recruitment event, to which recruitment to C. taxifolia was very high. After 12 months, few clams remained in either habitat, and those that remained showed little growth. Experimental manipulations of recruits demonstrated that all performance measures (survivorship, growth and condition) were significantly reduced in C. taxifolia sediments compared to unvegetated sediments. Exploration of potential mechanisms responsible for the reduced performance in C. taxifolia sediments showed that water flow and water column dissolved oxygen (DO) were significantly reduced under the canopy of C. taxifolia and that sediment anoxia was significantly higher and sediment sulphides greater in C. taxifolia sediments. However, phytoplankton abundance (an indicator of food supply) was significantly higher in C. taxifolia sediments than in unvegetated ones. Our results demonstrate that recruitment of native species to habitat-forming invasive species can reduce growth, condition and survivorship and that studies conducted at the community level may lead to erroneous conclusions about the impacts of invaders and should include studies on life-history traits, particularly juveniles. © 2008 Springer-Verlag

Engineering strategies to decode and enhance the genomes of coral symbionts

© 2017 Levin, Voolstra, Agrawal, Steinberg, Suggett and van Oppen. Elevated sea surface temperatures from a severe and prolonged El Niño event (2014-2016) fueled by climate change have resulted in mass coral bleaching (loss of dinoflagellate photosymbionts, Symbiodinium spp., from coral tissues) and subsequent coral mortality, devastating reefs worldwide. Genetic variation within and between Symbiodinium species strongly influences the bleaching tolerance of corals, thus recent papers have called for genetic engineering of Symbiodinium to elucidate the genetic basis of bleaching-relevant Symbiodinium traits. However, while Symbiodinium has been intensively studied for over 50 years, genetic transformation of Symbiodinium has seen little success likely due to the large evolutionary divergence between Symbiodinium and other model eukaryotes rendering standard transformation systems incompatible. Here, we integrate the growing wealth of Symbiodinium next-generation sequencing data to design tailored genetic engineering strategies. Specifically, we develop a testable expression construct model that incorporates endogenous Symbiodinium promoters, terminators, and genes of interest, as well as an internal ribosomal entry site from a Symbiodinium virus. Furthermore, we assess the potential for CRISPR/Cas9 genome editing through new analyses of the three currently available Symbiodinium genomes. Finally, we discuss how genetic engineering could be applied to enhance the stress tolerance of Symbiodinium, and in turn, coral reefs

Kelp forest restoration in Australia

Kelp forests dominate the rocky coasts of temperate Australia and are the foundation of the Great Southern Reef. Much like terrestrial forests, these marine forests create complex habitat for diverse communities of flora and fauna. Kelp forests also support coastal food-webs and valuable fisheries and provide a suite of additional ecosystem services. In many regions of Australia and around the world, kelp forests are in decline due to ocean warming, overgrazing, and pollution. One potential tool in the conservation and management of these important ecosystems is habitat restoration, the science and practice of which is currently undergoing substantial expansion. We summarize the present state of Australian kelp forests and emphasize that consideration of the initial drivers of kelp decline is a critical first step in restoration. With a focus on Australian examples, we review methods, implementation and outcomes of kelp forest restoration, and discuss suitable measures of success and the estimated costs of restoration activities. We propose a workflow and decision system for kelp forest restoration that identifies alternative pathways for implementation and acknowledges that under some circumstances restoration at scale is not possible or feasible. As a case study, we then apply the Society for Ecological Restoration’s 5-star evaluation to Operation Crayweed, Australia’s primary example of kelp forest restoration. Overall, no single method of kelp forest restoration is suitable for all situations, but outcomes can be optimized by ameliorating the driver(s) of kelp decline and achieving ongoing natural recruitment of kelp. Whilst scalability of kelp forest restoration to the seascape-scale remains a considerable challenge, the present review should provide a platform for future restoration efforts. However, it is also crucial to emphasize that the challenges of restoration place a high value on preventative conservation and protection of existing kelp forest ecosystems – prevention is invariably better than cure

Legacy Metal Contaminants and Excess Nutrients in Low Flow Estuarine Embayments Alter Composition and Function of Benthic Bacterial Communities.

Coastal systems such as estuaries are threatened by multiple anthropogenic stressors worldwide. However, how these stressors and estuarine hydrology shape benthic bacterial communities and their functions remains poorly known. Here, we surveyed sediment bacterial communities in poorly flushed embayments and well flushed channels in Sydney Harbour, Australia, using 16S rRNA gene sequencing. Sediment samples were collected monthly during the Austral summer-autumn 2014 at increasing distance from a large storm drain in each channel and embayment. Bacterial communities differed significantly between sites that varied in proximity to storm drains, with a gradient of change apparent for sites within embayments. We explored this pattern for embayment sites with analysis of RNA-Seq gene expression patterns and found higher expression of multiple genes involved in bacterial stress response far from storm drains, suggesting that bacterial communities close to storm drains may be more tolerant of localised anthropogenic stressors. Several bacterial groups also differed close to and far from storm drains, suggesting their potential utility as bioindicators to monitor contaminants in estuarine sediments. Overall, our study provides useful insights into changes in the composition and functioning of benthic bacterial communities as a result of multiple anthropogenic stressors in differing hydrological conditions

Coastal connectivity and spatial subsidy from a microbial perspective

© 2016 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd. The transfer of organic material from one coastal environment to another can increase production in recipient habitats in a process known as spatial subsidy. Microorganisms drive the generation, transformation, and uptake of organic material in shallow coastal environments, but their significance in connecting coastal habitats through spatial subsidies has received limited attention. We address this by presenting a conceptual model of coastal connectivity that focuses on the flow of microbially mediated organic material in key coastal habitats. Our model suggests that it is not the difference in generation rates of organic material between coastal habitats but the amount of organic material assimilated into microbial biomass and respiration that determines the amount of material that can be exported from one coastal environment to another. Further, the flow of organic material across coastal habitats is sensitive to environmental change as this can alter microbial remineralization and respiration rates. Our model highlights microorganisms as an integral part of coastal connectivity and emphasizes the importance of including a microbial perspective in coastal connectivity studies

Chemical mediation of coral larval settlement by crustose coralline algae

The majority of marine invertebrates produce dispersive larvae which, in order to complete their life cycles, must attach and metamorphose into benthic forms. This process, collectively referred to as settlement, is often guided by habitat-specific cues. While the sources of such cues are well known, the links between their biological activity, chemical identity, presence and quantification in situ are largely missing. Previous work on coral larval settlement in vitro has shown widespread induction by crustose coralline algae (CCA) and in particular their associated bacteria. However, we found that bacterial biofilms on CCA did not initiate ecologically realistic settlement responses in larvae of 11 hard coral species from Australia, Guam, Singapore and Japan. We instead found that algal chemical cues induce identical behavioral responses of larvae as per live CCA. We identified two classes of CCA cell wall-associated compounds - glycoglycerolipids and polysaccharides - as the main constituents of settlement inducing fractions. These algae-derived fractions induce settlement and metamorphosis at equivalent concentrations as present in CCA, both in small scale laboratory assays and under flow-through conditions, suggesting their ability to act in an ecologically relevant fashion to steer larval settlement of corals. Both compound classes were readily detected in natural samples