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1. Transcriptomic responses to extreme low salinity among locally adapted populations of Olympia oyster ( Ostrea lurida )

   https://doi.org/10.1111/mec.14863  

   Maynard, Ashley ; Bible, Jillian M. ; Pespeni, Melissa H. ; Sanford, Eric ; Evans, Tyler G. ( October 2018 , Molecular Ecology)

   The Olympia oyster (Ostrea lurida) is a foundation species inhabiting estuaries along the North American west coast. In California estuaries,O. luridais adapted to local salinity regimes and populations differ in low salinity tolerance. In this study, oysters from three California populations were reared for two generations in a laboratory common garden and subsequently exposed to low salinity seawater. Comparative transcriptomics was then used to understand species‐level responses to hyposmotic stress and population‐level mechanisms underlying divergent salinity tolerances. Gene expression patterns indicate Olympia oysters are sensitive to hyposmotic stress: All populations respond to low salinity by up‐regulating transcripts indicative of protein unfolding,DNAdamage and cell cycle arrest after sub‐lethal exposure. AmongO. luridapopulations, transcriptomic profiles differed constitutively and in response to low salinity. Despite two generations in common‐garden conditions, transcripts encoding apoptosis modulators were constitutively expressed at significantly different levels in the most tolerant population. Expression of cell death regulators may facilitate cell fate decisions when salinity declines. Following low salinity exposure, oysters from the more tolerant population expressed a small number of mRNAs at significantly higher levels than less tolerant populations. Proteins encoded by these transcripts regulate ciliary activity within the mantle cavity and may function to prolong valve closure and reduce mortality in low salinity seawater. Collectively, gene expression patterns suggest sub‐lethal impacts of hyposmotic stress in Olympia oysters are considerable and that even oysters with greater low salinity tolerance may be vulnerable to future freshwater flooding events.

    

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2. Genetic and physical interactions between the organellar mechanosensitive ion channel homologs MSL 1, MSL 2, and MSL 3 reveal a role for inter‐organellar communication in plant development

   https://doi.org/10.1002/pld3.124  

   Lee, Josephine S. ; Wilson, Margaret E. ; Richardson, Ryan A. ; Haswell, Elizabeth S. ( March 2019 , Plant Direct)

   Plant development requires communication on many levels, including between cells and between organelles within a cell. For example, mitochondria and plastids have been proposed to be sensors of environmental stress and to coordinate their responses. Here we present evidence for communication between mitochondria and chloroplasts during leaf and root development, based on genetic and physical interactions between threeMechanosensitive channel ofSmall conductance‐Like (MSL) proteins fromArabidopsis thaliana.MSLproteins areArabidopsishomologs of the bacterialMechanosensitivechannel ofSmall conductance (MscS), which relieves cellular osmotic pressure to protect against lysis during hypoosmotic shock.MSL1 localizes to the inner mitochondrial membrane, whileMSL2 andMSL3 localize to the inner plastid membrane and are required to maintain plastid osmotic homeostasis during normal growth and development. In this study, we characterized the phenotypic effect of a genetic lesion inMSL1, both in wild type and inmsl2 msl3mutant backgrounds.msl1single mutants appear wild type for all phenotypes examined. The characteristic leaf rumpling inmsl2 msl3double mutants was exacerbated in themsl1 msl2 msl3triple mutant. However, the introduction of themsl1lesion into themsl2 msl3mutant background suppressed othermsl2 msl3mutant phenotypes, including ectopic callus formation, accumulation of superoxide and hydrogen peroxide in the shoot apical meristem, decreased root length, and reduced number of lateral roots. All these phenotypes could be recovered by molecular complementation with a transgene containing a wild type version ofMSL1. In yeast‐based interaction studies,MSL1 interacted with itself, but not withMSL2 orMSL3. These results establish that the abnormalities observed inmsl2 msl3double mutants is partially dependent on the presence of functionalMSL1 and suggest a possible role for communication between plastid and mitochondria in seedling development.

    

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3. Effect of Salinity on DMSP Production in Gambierdiscus belizeanus (Dinophyceae)

   https://doi.org/10.1111/jpy.12923  

   Gwinn, Jessica K. ; Robertson, Alison ; Kiene, Ronald P. ( October 2019 , Journal of Phycology)

   Dimethylsulfoniopropionate (DMSP) is produced by many species of marine phytoplankton and has been reported to provide a variety of beneficial functions including osmoregulation. Dinoflagellates are recognized as majorDMSPproducers; however, accumulation has been shown to be highly variable in this group. We explored the effect of hyposaline transfer inGambierdiscus belizeanusbetween ecologically relevant salinities (36 and 31) onDMSPaccumulation, Chla, cell growth, and cell volume, over 12 d. Our results showed thatG. belizeanusmaintained an intracellularDMSPcontent of 16.3 pmol cell⁻¹and concentration of 139 mMin both salinities. Although this intracellular concentration was near the median reported for other dinoflagellates, the cellular content achieved byG. belizeanuswas the highest reported of any dinoflagellate thus far, owing mainly to its large size.DMSPlevels were not significantly affected by salinity treatment but did change over time during the experiment. Salinity, however, did have a significant effect on the ratio ofDMSP:Chla, suggesting that salinity transfer ofG. belizeanusinduced a physiological response other thanDMSPadjustment. A survey ofDMSPcontent in a variety ofGambierdiscusspecies and strains revealed relatively highDMSPconcentrations (1.0–16.4 pmol cell⁻¹) as well as high intrageneric and intraspecific variation. We conclude that, althoughDMSPmay not be involved in long‐term (3–12 d) osmoregulation in this species,G. belizeanusand otherGambierdiscusspecies may be important contributors toDMSPproduction in tropical benthic microalgal communities due to their large size and high cellular content.

    

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4. Use of the high‐affinity phosphate transporter gene, pstS , as an indicator for phosphorus stress in the marine diazotroph Crocosphaera watsonii ( Chroococcales , Cyanobacteria )

   https://doi.org/10.1111/jpy.12863  

   Pereira, Nicole ; Shilova, Irina N. ; Zehr, Jonathan P. ; Roleda, ed., M. ( May 2019 , Journal of Phycology)

   The marine diazotrophCrocosphaera watsoniiprovides fixed carbon (C) and nitrogen (N) to open‐ocean regimes, where nutrient deficiency controls productivity. The growth ofCrocosphaeracan be limited by low phosphorus (P) concentrations in these oligotrophic environments. Biomarkers such as the high‐affinityABCtransporter phosphate‐binding gene,pstS, are commonly used to monitor when such organisms are under P stress; however, transcriptional regulation of these markers is often complex and not well‐understood. In this study, we interrogated changes inpstStranscript levels inC. watsoniicells under P starvation, and in response to added dissolved inorganic phosphorus (DIP), dissolved organic phosphorus (DOP), and changing light levels. We observed elevated relativepstStranscript levels inC. watsoniiWH8501 atDIPconcentrations below 60 and above 20 nmol · L⁻¹. Transcript levels were suppressed by both inorganic and bioavailable organic phosphorus; however, the P stress response was more sensitive toDIPthanDOPsources. Increasing light intensity resulted in increased relativepstStranscript abundances independently of low external P, and seemed to exacerbate the physiological effects of P stress. The variable response to different P compounds and rapid and transient influence of high light onpstStranscript abundances suggests thatpstSis an indicator of internal P status inCrocosphaera.

    

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5. TaADF4 , an actin‐depolymerizing factor from wheat, is required for resistance to the stripe rust pathogen Puccinia striiformis f. sp. tritici

   https://doi.org/10.1111/tpj.13459  

   Zhang, Bing ; Hua, Yuan ; Wang, Juan ; Huo, Yan ; Shimono, Masaki ; Day, Brad ; Ma, Qing ( February 2017 , The Plant Journal)

   Actin filament assembly in plants is a dynamic process, requiring the activity of more than 75 actin‐binding proteins. Central to the regulation of filament assembly and stability is the activity of a conserved family of actin‐depolymerizing factors (ADFs), whose primarily function is to regulate the severing and depolymerization of actin filaments. In recent years, the activity ofADFproteins has been linked to a variety of cellular processes, including those associated with response to stress. Herein, a wheatADFgene,TaADF4,was identified and characterized.TaADF4encodes a 139‐amino‐acid protein containing five F‐actin‐binding sites and two G‐actin‐binding sites, and interacts with wheat (Triticum aestivum) Actin1 (TaACT1),in planta. Following treatment of wheat, separately, with jasmonic acid, abscisic acid or with the avirulent race,CYR23, of the stripe rust pathogenPuccinia striiformisf. sp.tritici, we observed a rapid induction in accumulation ofTaADF4mRNA. Interestingly, accumulation ofTaADF4mRNAwas diminished in response to inoculation with a virulent race,CYR31. Silencing ofTaADF4resulted in enhanced susceptibility toCYR23, demonstrating a role forTaADF4in defense signaling. Using a pharmacological‐based approach, coupled with an analysis of host response to pathogen infection, we observed that treatment of plants with the actin‐modifying agent latrunculin B enhanced resistance toCYR23, including increased production of reactive oxygen species and enhancement of localized hypersensitive cell death. Taken together, these data support the hypothesis thatTaADF4 positively modulates plant immunity in wheat via the modulation of actin cytoskeletal organization.

    

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