Seed Cryopreservation and Germination of Rhus glabra and the Critically Endangered Species Rhus michauxii

Rhus michauxii is a perennial rhizomatous shrub native to the southeastern United States that is found mainly in sunny, dry, open rocky or sandy woodlands. Moreover, it is found on ridges or river bluffs in the inner coastal plane and lower piedmont of Virginia, Georgia, and the Carolinas. Habitat conversion to agriculture, suppression of fires, and low reproduction have caused R. michauxii to become rare and it is now federally listed as threatened. Methods are needed to multiply and conserve R. michauxii. Protocols were developed for seed cryopreservation, in vitro germination, and micropropagation for R. glabra and R. michauxii. Seed scarification in concentrated sulfuric acid for 6 h and germination on ½ MS medium resulted in germination up to 96% for control and cryopreserved seeds of R. glabra and 70 and 40% for control and cryopreserved seeds of R. michauxii. Shortly after germination in vitro, young seedlings were established in a greenhouse potting mix providing new plants from the endemic Georgia R. michauxii populations. Several of the findings meet goals within the R. michauxii recovery plan by providing methods for sexual and asexual multiplication and long-term seed storage under cryogenic conditions. The protocols developed will assist in the safeguarding and conservation of dwindling natural R. michauxii populations.

Different components of the RNAi machinery are required for conidiation, ascosporogenesis, virulence, DON production and fungal inhibition by exogenous dsRNA in the Head Blight pathogenFusarium graminearum

Gene silencing through RNA interference (RNAi) shapes many biological processes in filamentous fungi, including pathogenicity. In this study we explored the requirement of key components of fungal RNAi machinery, including DICER-like 1 and 2 (FgDCL1,FgDCL2), ARGONAUTE 1 and 2 (FgAGO1,FgAGO2), AGO-interacting proteinFgQIP (QDE2-interacting protein), RecQ helicase (FgQDE3), and four RNA-dependent RNA polymerases (FgRdRP1,FgRdRP2,FgRdRP3,FgRdRP4), in the ascomycete mycotoxin-producing fungal pathogenFusarium graminearum(Fg) for sexual and asexual multiplication, pathogenicity, and its sensitivity to double-stranded (ds)RNA. We corroborate and extend earlier findings that conidiation, ascosporogenesis and Fusarium Head Blight (FHB) symptom development require an operable RNAi machinery. The involvement of RNAi in conidiation is dependent on environmental conditions as it is detectable only under low light (< 2 µmol m−2s−1). Although both DCLs and AGOs partially share their functions, the sexual ascosporogenesis is mediated primarily byFgDCL1 andFgAGO2, whileFgDCL2 andFgAGO1 contribute to asexual conidia formation and germination.FgDCL1 andFgAGO2 also account for pathogenesis as their knock-out (KO) results in reduced FHB development. Apart from KO mutantsΔdcl2andΔago1, mutantsΔrdrp2, Δrdrp3, Δrdrp4, Δqde3andΔqipare strongly compromised for conidiation, while KO mutations in allRdPRs, QDE3andQIPstrongly affect ascosporogenesis. Analysis of trichothecenes mycotoxins in wheat kernels showed that the relative amount of deoxynivalenol (DON), calculated as [DON] per amount of fungal genomic DNA, was reduced in all spikes infected with RNAi mutants, suggesting the possibility that the fungal RNAi pathways affectFg’s DON production in wheat spikes. Moreover, gene silencing by exogenous target gene specific dsRNA (spray-induced gene silencing, SIGS) is dependent on fungal DCLs, AGOs, and QIP, but not on QDE3. Together these data show that inF. graminearumdifferent key components of the RNAi machinery are crucial in different steps of fungal development and pathogenicity.

Regulation of sexual differentiation is linked to invasion in malaria parasites

SummaryIn the malaria parasite Plasmodium falciparum, the switch from asexual multiplication to sexual differentiation into gametocytes is essential for transmission to mosquitos. One of the key determinants of sexual commitment is the transcription factor PfAP2-G, which has been proposed to orchestrate this crucial cell fate decision by driving expression of gametocyte genes. We show conclusively that PfAP2-G is a transcriptional activator of gametocyte genes and identify the earliest known markers expressed during commitment. Remarkably, we also find that in sexually committed cells, PfAP2-G is associated with the promoters of genes important for red blood cell invasion and activates them through its interactions with a second transcription factor. We thus demonstrate an intriguing transcriptional link between the apparently opposing processes of red blood cell invasion and gametocytogenesis that is coordinated by the master regulator PfAP2-G. This finding has important implications for the development of new anti-malarial drugs that block the invasion of red blood cells by sexually committed cells, thereby preventing parasite transmission.

Re-evaluation of endogenous development of Eimeria bareillyi Gill, Chhabra and Lall, 1963 in water buffalo (Bubalus bubalis)

Water buffalo (Bubalus bubalis) is important for the economy of Asia, South America and parts of Europe. Coccidiosis is an important cause of neonatal mortality in livestock, including buffalo. Of more than 12 species of Eimeria in buffalo, Eimeria bareillyi is the most pathogenic. There are uncertainties concerning its asexual and sexual development. During a previously reported outbreak of fatal enteritis associated with E. bareillyi in buffaloes in the Netherlands, sections of small intestine were re-evaluated histologically and by transmission electron microscopy (TEM) to seek details of endogenous development. Profuse asexual multiplication occurred in the jejunum and ileum. Light microscopic examination revealed that parasites divided in two (probably endodyogeny) or more organisms. There were two or more generations of morphologically different merozoites; some of these observations were confirmed by TEM. Details of gametogonic development, including oocyst wall formation are provided. Schizogonic and gametogonic development described in the present study can serve as a guide for differential diagnosis of Eimeria species in histological sections of intestines of buffaloes.

‘Cerejeira da mata’ and ‘guabijuzeiro’ propagation by air layering

‘Guabijuzeiro’ and ‘cerejeira da mata’ are plant species from the Myrtaceae family, with many difficulties in asexual multiplication. Thus, the aim of this study was to evaluate ‘cerejeira da mata’ (Eugenia involucrata DC.) tree and ‘guabijuzeiro’ [Myrcianthes pungens (Berg) Legrand] tree propagation by air layering, using different IBA concentrations (0, 1000 , 2000 and 3000 mg L-1) and materials to wrap the substrate (transparent plastic, black plastic and transparent plastic + aluminum foil). The experimental design for both experiments was a randomized blocks, in a 3 x 4 factorial (wrapping material x IBA concentration), with three repetitions of five air layering each. After 180 days, the percentage of rooting, length and number of roots were evaluated. Sixty days after rooting the percentage of survival plants were evaluated. The air layering technique was not efficient in the ‘guabijuzeiro’ propagation. This technique could be used in ‘cerejeira da mata’ plants without the IBA application and using transparent plastic, but with low performance.

Sexual reproduction in the fungal foliar pathogen Zymoseptoria tritici is driven by antagonistic density-dependence mechanisms

This study provides empirical evidence for antagonistic density-dependence mechanisms driving sexual reproduction in the wheat fungal pathogen Zymoseptoria tritici. Biparental crosses with 12 increasing inoculum concentrations, in controlled conditions, showed that sexual reproduction in Z. tritici was impacted by an Allee effect due to mate limitation and a competition with asexual multiplication for resource allocation. We found that asexual multiplication was itself affected by competition for host resources between the two parental isolates, as illustrated by the decrease in asexual fruiting body density and sporulation intensity observed with increasing lesion density. Consistent with these results for controlled co-inoculation, we found that the intensity of sexual reproduction varied with both cropping period and the vertical position of the host tissues in the field. An optimal lesion density maximizing offspring (ascospores) number was established, and its eco-evolutionary consequences are considered here. Two ecological mechanisms may be involved: competition for resources between the two modes of reproduction (decrease in the host resources available for sexual reproduction due to their prior use in asexual multiplication), and competitive disequilibrium between the two parental isolates, due to differential interaction dynamics with the host, for example, leading to an imbalance between mating types. Conceptual models based on these results suggest that sexual reproduction plays a key role in the evolution of pathogenicity traits, including virulence and aggressiveness. Ecological knowledge about the determinants of sexual reproduction in Z. tritici may, therefore, open up new perspectives for the management of other fungal foliar pathogens with dual modes of reproduction.

Of jellyfish, fish, and humans

This paper follows my journey from childhood in Missouri, where I saw my first jellyfish, to the oceans of the world. Pelagic cnidarians and ctenophores (“jellies”) have been the focus of my career. I think my work has been relevant to the broader scientific community because jellies are predators and potential competitors of fish. In my early research, I quantitatively estimated the predation effects of jellies on zooplankton and ichthyoplankton. I found that most jellies are selective predators, with a few species having diets of only fish larvae or soft-bodied prey. As I learned more about the physical environment that jellies encounter, my early reductionist approach evolved into a more holistic approach. I thought the asexual multiplication from the attached polyp stage would be fundamental in determining jellyfish population size and that the effects of environmental variables could be tested experimentally. It also seemed that humans have changed the natural environment in ways favoring jellies over fish and jelly populations may have increased in developed, eutrophic, hypoxic, overfished, and warming coastal waters. Many opportunities were available that gave me a global perspective. I have persisted despite some difficulties because I love to learn and I am still having fun!

Trematoda (flukes)

The class Trematoda is the largest group of Platyhelminths and includes two subclasses: Aspidogastrea and Digenea. Trematodes, and particularly Digeneans, is a large group of organisms with significant medical and veterinary interest. Over 100 species of digenetic trematodes have been reported infecting humans. Although the significant mortality and morbidity that some of these infections cause, they are among the most neglected tropical diseases. Apart from their impact in public and animal health, the Digenea constitutes an intriguing group of organisms that has a vast interest in experimental biology. Systematics and taxonomy of this group constitute a challenge for biologists in relation to the difficulty entailed in the establishment of phylogenetic relationships between trematodes and the determination of valid diagnostic features. Moreover, their complex life cycles, using at least two hosts and alternating free-living and parasitic stages or sexual and asexual multiplication, constitute a paradigm of how organisms can evolve to become adapted to different biotic and abiotic environments to enhance survival. In this review, we briefly summarize the major features of trematodes in relation to both biological and medical areas.