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1. Phylogenomic Diversity Elucidates Mechanistic Insights into Lyme Borreliae-Host Association

   https://doi.org/10.1128/msystems.00488-22  

   Combs, Matthew ; Marcinkiewicz, Ashley L. ; Dupuis, Alan P. ; Davis, April D. ; Lederman, Patricia ; Nowak, Tristan A. ; Stout, Jessica L. ; Strle, Klemen ; Fingerle, Volker ; Margos, Gabriele ; et al ( August 2022 , mSystems)

   Gilbert, Jack A. (Ed.)

   ABSTRACT Host association—the selective adaptation of pathogens to specific host species—evolves through constant interactions between host and pathogens, leaving a lot yet to be discovered on immunological mechanisms and genomic determinants. The causative agents of Lyme disease (LD) are spirochete bacteria composed of multiple species of the Borrelia burgdorferi sensu lato complex, including B. burgdorferi ( Bb ), the main LD pathogen in North America—a useful model for the study of mechanisms underlying host-pathogen association. Host adaptation requires pathogens’ ability to evade host immune responses, such as complement, the first-line innate immune defense mechanism. We tested the hypothesis that different host-adapted phenotypes among Bb strains are linked to polymorphic loci that confer complement evasion traits in a host-specific manner. We first examined the survivability of 20 Bb strains in sera in vitro and/or bloodstream and tissues in vivo from rodent and avian LD models. Three groups of complement-dependent host-association phenotypes emerged. We analyzed complement-evasion genes, identified a priori among all strains and sequenced and compared genomes for individual strains representing each phenotype. The evolutionary history of ospC loci is correlated with host-specific complement-evasion phenotypes, while comparative genomics suggests that several gene families and loci are potentially involved in host association. This multidisciplinary work provides novel insights into the functional evolution of host-adapted phenotypes, building a foundation for further investigation of the immunological and genomic determinants of host association. IMPORTANCE Host association is the phenotype that is commonly found in many pathogens that preferential survive in particular hosts. The Lyme disease (LD)-causing agent, B. burgdorferi ( Bb ), is an ideal model to study host association, as Bb is mainly maintained in nature through rodent and avian hosts. A widespread yet untested concept posits that host association in Bb strains is linked to Bb functional genetic variation conferring evasion to complement, an innate defense mechanism in vertebrate sera. Here, we tested this concept by grouping 20 Bb strains into three complement-dependent host-association phenotypes based on their survivability in sera and/or bloodstream and distal tissues in rodent and avian LD models. Phylogenomic analysis of these strains further correlated several gene families and loci, including ospC , with host-specific complement-evasion phenotypes. Such multifaceted studies thus pave the road to further identify the determinants of host association, providing mechanistic insights into host-pathogen interaction. 

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2. Impact of Land Use Changes and Habitat Fragmentation on the Eco-epidemiology of Tick-Borne Diseases

   https://doi.org/10.1093/jme/tjaa209  

   Diuk-Wasser, Maria A ; VanAcker, Meredith C ; Fernandez, Maria P ( October 2020 , Journal of Medical Entomology)

   Reisen, William (Ed.)

   Abstract The incidence of tick-borne diseases has increased in recent decades and accounts for the majority of vector-borne disease cases in temperate areas of Europe, North America, and Asia. This emergence has been attributed to multiple and interactive drivers including changes in climate, land use, abundance of key hosts, and people’s behaviors affecting the probability of human exposure to infected ticks. In this forum paper, we focus on how land use changes have shaped the eco-epidemiology of Ixodes scapularis-borne pathogens, in particular the Lyme disease spirochete Borrelia burgdorferi sensu stricto in the eastern United States. We use this as a model system, addressing other tick-borne disease systems as needed to illustrate patterns or processes. We first examine how land use interacts with abiotic conditions (microclimate) and biotic factors (e.g., host community composition) to influence the enzootic hazard, measured as the density of host-seeking I. scapularis nymphs infected with B. burgdorferi s.s. We then review the evidence of how specific landscape configuration, in particular forest fragmentation, influences the enzootic hazard and disease risk across spatial scales and urbanization levels. We emphasize the need for a dynamic understanding of landscapes based on tick and pathogen host movement and habitat use in relation to human resource provisioning. We propose a coupled natural-human systems framework for tick-borne diseases that accounts for the multiple interactions, nonlinearities and feedbacks in the system and conclude with a call for standardization of methodology and terminology to help integrate studies conducted at multiple scales. 

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3. Disease tolerance alters host competence in a wild songbird

   https://doi.org/10.1098/rsbl.2021.0362  

   Ruden, Rachel M. ; Adelman, James S. ( October 2021 , Biology Letters)

   Individuals can express a range of disease phenotypes during infection, with important implications for epidemics. Tolerance, in particular, is a host response that minimizes the per-pathogen fitness costs of infection. Because tolerant hosts show milder clinical signs and higher survival, despite similar pathogen burdens, their potential for prolonged pathogen shedding may facilitate the spread of pathogens. To test this, we simulated outbreaks of mycoplasmal conjunctivitis in house finches, asking how the speed of transmission varied with tissue-specific and behavioural components of tolerance, milder conjunctivitis and anorexia for a given pathogen load, respectively. Because tissue-specific tolerance hinders pathogen deposition onto bird feeders, important transmission hubs, we predicted it would slow transmission. Because behavioural tolerance should increase interactions with bird feeders, we predicted it would speed transmission. Our findings supported these predictions, suggesting that variation in tolerance could help identify individuals most likely to transmit pathogens. 

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4. Scaling of phloem hydraulic resistance in stems and leaves of the understory angiosperm shrub Illicium parviflorum

   https://doi.org/10.1002/ajb2.1241  

   ( February 2019 , American Journal of Botany)

   Recent studies in canopy‐dominant trees revealed axial scaling of phloem structure. However, whether this pattern is found in woody plants of the understory, the environment of most angiosperms from the ANA grade (Amborellales‐Nymphaeales‐Austrobaileyales), is unknown.

   We used seedlings and adult plants of the understory tropical shrubIllicium parviflorum,a member of the lineage Austrobaileyales, to explore the anatomy and physiology of the phloem in their aerial parts, including changes through ontogeny.

   Adult plants maintain a similar proportion of phloem tissue across stem diameters, but larger conduit dimensions and number cause the hydraulic resistance of the phloem to decrease toward the base of the plant. Small sieve plate pores resulted in an overall higher sieve tube hydraulic resistance than has been reported in other woody angiosperms. Sieve elements increase in size from minor to major leaf veins, but were shorter and narrower in petioles. The low carbon assimilation rates of seedlings and mature plants contrasted with a 3‐fold higher phloem sap velocity in seedlings, suggesting that phloem transport velocity is modulated through ontogeny.

   The overall architecture of the phloem tissue in this understory angiosperm shrub scales in a manner consistent with taller trees that make up the forest canopy. Thus, the evolution of larger sieve plate pores in canopy‐dominant trees may have played a key role in allowing woody angiosperms to extend beyond their understory origins.

    

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5. Citrus miraculin‐like protein hijacks a viral movement‐related p33 protein and induces cellular oxidative stress in defence against Citrus tristeza virus

   https://doi.org/10.1111/pbi.13523  

   Sun, Yong‐Duo ; Zhang, Lei ; Folimonova, Svetlana Y. ( December 2020 , Plant Biotechnology Journal)

   To defend against pathogens, plants have developed a complex immune system, which recognizes the pathogen effectors and mounts defence responses. In this study, the p33 protein ofCitrus tristeza virus(CTV), a viral membrane‐associated effector, was used as a molecular bait to explore virus interactions with host immunity. We discovered thatCitrus macrophyllamiraculin‐like protein 2 (CmMLP2), a member of the soybean Kunitz‐type trypsin inhibitor family, targets the viral p33 protein. The expression ofCmMLP2was up‐regulated by p33 in the citrus phloem‐associated cells. Knock‐down of theMLP2expression in citrus plants resulted in a higher virus accumulation, while the overexpression ofCmMLP2reduced the infectivity of CTV in the plant hosts. Further investigation revealed that, on the one hand, binding of CmMLP2 interrupts the cellular distribution of p33 whose proper function is necessary for the effective virus movement throughout the host. On the other hand, the ability of CmMLP2 to reorganize the endomembrane system, amalgamating the endoplasmic reticulum and the Golgi apparatus, induces cellular stress and accumulation of the reactive oxygen species, which inhibits the replication of CTV. Altogether, our data suggest that CmMLP2 employs a two‐way strategy in defence against CTV infection.

    

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