Characterization and pathogenicity of a Pythium aphanidermatum isolate causing ‘damping off’ in pepper seedlings

<p>The production of the pepper seedling (<em>Capsicum annuum</em>) is affected by the fungal complex that causes the ‘damping-off’, in which some species of the oomycete <em>Pythium</em> spp., stand out. The objective of the present study was to identify the causal agent of the death of pepper plants and evaluate its pathogenicity in pepper seeds and seedlings. A fast and aggressive growing oomycete was isolate from pepper plants, morphologically identified as P. aphanidermatum based on its sexual and asexual reproduction structures and, by molecular techniques. This isolate had a high degree of<em> in vitro</em> pathogenicity in pre-emergence and post-emergence in chile, showing 100% mortality. In addition, it presented a high rate of mycelial growth in different culture media (V8-Agar, Corn Agar, Corn Potato Agar, Potato Dextrose Agar, Czapek &amp; Oat Agar), being in V8-Agar medium the only medium where it developed reproduction structures sexual and asexual. The isolation presented a mycelial growth rate of 58.3 ± 0.3 mm / day at 26 ± 2 °C in PDA medium. Due to its rapid growth and its high degree of pathogenicity <em>in vitro</em>, it is an unusual and aggressive isolate for pepper seedlings.</p>

Peroxin FgPEX22-Like Is Involved in FgPEX4 Tethering and Fusarium graminearum Pathogenicity

Peroxisomes are essential organelles that play important roles in a variety of biological processes in eukaryotic cells. To understand the synthesis of peroxisomes comprehensively, we identified the gene FgPEX22-like, encoding FgPEX22-like, a peroxin, in Fusarium graminearum. Our results showed that although FgPEX22-like was notably different from other peroxins (PEX) in Saccharomyces cerevisiae, it contained a predicted PEX4-binding site and interacted with FgPEX4 as a rivet protein of FgPEX4. To functionally characterize the roles of FgPEX22-like in F. graminearum, we performed homologous recombination to construct a deletion mutant (ΔPEX22-like). Analysis of the mutant showed that FgPEX22-like was essential for sexual and asexual reproduction, fatty acid utilization, pathogenicity, and production of the mycotoxin deoxynivalenol. Deletion of FgPEX22-like also led to increased production of lipid droplets and decreased elimination of reactive oxygen species. In addition, FgPEX22-like was required for the biogenesis of Woronin bodies. Taken together, our data demonstrate that FgPEX22-like is a peroxin in F. graminearum that interacts with PEX4 by anchoring PEX4 at the peroxisomal membrane and contributes to the peroxisome function in F. graminearum.

Modeling the efficacy of CRISPR gene drive for schistosomiasis control

CRISPR gene drives could revolutionize the control of infectious diseases by accelerating the spread of engineered traits that limit parasite transmission in wild populations. While much effort has been spent developing gene drives in mosquitoes, gene drive technology in molluscs has received little attention despite the role of freshwater snails as obligate, intermediate hosts of parasitic flukes causing schistosomiasis -- a disease of poverty affecting more than 200 million people worldwide. A successful drive in snails must overcome self-fertilization, which prevents a drive's spread. Simultaneous hermaphroditism is a feature of snails -- distinct from gene drive model organisms -- and is not yet incorporated in gene drive models of disease control. Here we developed a novel population genetic model accounting for snails' sexual and asexual reproduction, susceptibility to parasite infection regulated by multiple alleles, fitness differences between genotypes, and a range of drive characteristics. We then integrated this model with an epidemiological model of schistosomiasis transmission and snail population dynamics. Simulations showed that gene drive establishment can be hindered by a variety of biological and ecological factors, including selfing. However, our model suggests that, under a range of conditions, gene drive mediated immunity in snails could maintain rapid disease reduction achieved by annual chemotherapy treatment of the human population, leading to long-term elimination. These results indicate that gene drives, in coordination with existing public health measures, may become a useful tool to reduce schistosomiasis burden in selected transmission settings with effective CRISPR construct design and close evaluation of the genetic and ecological landscape.

Advances in understanding the epidemiology, molecular biology and control of net blotch and the net blotch barley interaction

Net blotches are the most widely distributed foliar diseases of barley worldwide, causing significant losses in grain yield. They occur as net form net blotch, caused by Pyrenophora teres f. teres and spot form net blotch caused by P. teres f. maculata. Both sexual and asexual reproduction play a role in the P. teres disease cycles leading to changes in genetic variation of populations. Breeding programs have to keep pace with pathogenic changes and ensure different sources of resistance are present in current barley cultivars. Knowledge of the genetic architecture and genes involved in virulence is thus vital to increase the durability of net blotch resistance in barley cultivars. This chapter explores the molecular biology, life-cycle and epidemiology of the net blotch fungi and discusses the key challenges we are facing in managing the net blotches using both fungicide resistance and breeding strategies to achieve durable disease resistance in barley.

ASF1 activation PI3K/AKT pathway regulates sexual and asexual development in filamentous ascomycete

Sexual and asexual reproduction is ubiquitous in eukaryotes. PI3K/AKT signaling pathway can modulate sexual reproduction in mammals. However, this signaling pathway modulating sexual and asexual reproduction in fungi is scarcely understood. SeASF1, a SeH4 chaperone, could manipulate sexual and asexual reproduction of Stemphylium eturmiunum. SeDJ-1, screened from SeΔasf1 transcriptome, was confirmed to regulate sexual and asexual development by RNAi, of which the mechanism was demonstrated by detecting transcriptional levels and protein interactions of SeASF1, SeH4 and SeDJ-1 by qRT-PCR, and Y2H, Co-IP and Pull-down, respectively. SeASF1 coupling SeH4 bound SeDJ-1 to arouse the sexual and asexual activity. In S. eturmiunum genome, SeDJ-1 was upstream while SeGSK3 was downstream in PI3K/AKT signaling pathway. Moreover, SeDJ-1 interacted with SePI3K or SeGSK3 in vivo and in vitro. Significantly, SeDJ-1 or SePI3K could effectively stimulate sexual activity alone, but SePI3K could recover the sexual development of SiSeDJ-1.SeDJ-1-M6 was a critical segment for interaction of SeDJ-1 with SePI3K. SeDJ-1-M6 played a critical role in irritating sexual reproduction in SiSePI3K, which further uncovered the regulated mechanism of SeDJ-1. SeASF1 coupling SeH4 motivates SeDJ-1 to arouse SePI3K involved in sexual reproduction. Thus, SeASF1 can activate PI3K/AKT signaling pathway to regulate sexual and asexual development in filamentous ascomycete.

RH17 restricts reproductive fate and represses autonomous seed coat development in sexual Arabidopsis

ABSTRACT Plant sexual and asexual reproduction through seeds (apomixis) is tightly controlled by complex gene regulatory programs, which are not yet fully understood. Recent findings suggest that RNA helicases are required for plant germline development. This resembles their crucial roles in animals, where they are involved in controlling gene activity and the maintenance of genome integrity. Here, we identified previously unknown roles of Arabidopsis RH17 during reproductive development. Interestingly, RH17 is involved in repression of reproductive fate and of elements of seed development in the absence of fertilization. In lines carrying a mutant rh17 allele, development of supernumerary reproductive cell lineages in the female flower tissues (ovules) was observed, occasionally leading to formation of two embryos per seed. Furthermore, seed coat, and putatively also endosperm development, frequently initiated autonomously. Such induction of several features phenocopying distinct elements of apomixis by a single mutation is unusual and suggests that RH17 acts in regulatory control of plant reproductive development. Furthermore, an in-depth understanding of its action might be of use for agricultural applications.

Seasonal variation of genotypes and reproductive plasticity in a facultative clonal freshwater invertebrate animal (Hydra oligactis) living in a temperate lake

Facultative sexual organisms combine sexual and asexual reproduction within a single life cycle, often switching between reproductive modes depending on environmental conditions. These organisms frequently inhabit variable seasonal environments, where favourable periods alternate with unfavourable periods, generating temporally varying selection pressures that strongly influence life history decisions and hence population dynamics. Due to the rapidly accelerating changes in our global environment today, understanding the dynamics of and genetic changes in facultative sexual populations inhabiting seasonal environments is critical to assess and prepare for additional challenges that will affect such ecosystems. In this study we aimed at obtaining insights of the seasonal population dynamics of the facultative sexual freshwater cnidarian Hydra oligactis through a combination of Restriction-site Associated Sequencing (RAD-Seq) genotyping and the collection of phenotypic data on the reproductive strategy of field-collected hydra strains. We found no significant genetic change during the two years in the study population. Clone lines were detected between seasons and even years, suggesting that clonal lineages can persist for a long time in a natural population. We also found that distinct genotypes differ in sexual reproduction frequency, but these differences did not affect whether genotypes reappeared across samplings. Our study describes changes in population genetic structure across the seasons in a hydra population for the first time, providing key insights into the biology of the species, while also contributing to understanding the population biology of facultative sexual species inhabiting freshwater ecosystems.

Flood disturbance affects morphology and reproduction of woody riparian plants

Riparian forests are structured and maintained by their hydrology. Woody riparian plants typically adapt to the local flood regime to maximise their likelihood of survival and reproductive success. Understanding how extant trees form and reproduce in response to flood disturbance is crucial for predicting vegetation changes and informing restoration. Working in a temperate evergreen riparian forest, we aimed to determine whether disturbance-based responses of plants found in other ecosystems also typify woody plants in riparian forests where disturbances are often mild or chronic, non-lethal, annual events. Using plant surveys and 20-year modelled hydrological data, we examined whether (1) the morphology (main stem diameter, height, crown width, crown extent, stem leaning) and (2) reproduction type (sexual and asexual reproduction) and extent of three dominant woody species (Eucalyptus camphora, Leptospermum lanigerum and Melaleuca squarrosa) vary with flood regime (flood frequency and flood duration); and (3) whether different morphology is associated with different reproductive strategies. Increased flooding generally resulted in increased stem numbers and greater stem leaning—morphologies associated with asexual reproduction—of our study species. More frequent flooding also reduced plant size and sexual reproduction in E. camphora. Sexual reproduction in the studied species was more common in taller plants with single, more upright stems in good condition. Flexible morphology and plastic reproductive strategy may constitute an adaptation of trees to mild or chronic disturbance in floodplains. Our findings suggest that flood regime (i.e. variable frequency and duration of flooding events) is critical to the structural integrity and self-maintenance of species-diverse riparian forests.

Whole-Body Regeneration in the Lobate Ctenophore Mnemiopsis leidyi

Ctenophores (a.k.a. comb jellies) are one of the earliest branching extant metazoan phyla. Adult regenerative ability varies greatly within the group, with platyctenes undergoing both sexual and asexual reproduction by fission while others in the genus Beroe having completely lost the ability to replace missing body parts. We focus on the unique regenerative aspects of the lobate ctenophore, Mnemiopsis leidyi, which has become a popular model for its rapid wound healing and tissue replacement, optical clarity, and sequenced genome. M. leidyi’s highly mosaic, stereotyped development has been leveraged to reveal the polar coordinate system that directs whole-body regeneration as well as lineage restriction of replacement cells in various regenerating organs. Several cell signaling pathways known to function in regeneration in other animals are absent from the ctenophore’s genome. Further research will either reveal ancient principles of the regenerative process common to all animals or reveal novel solutions to the stability of cell fates and whole-body regeneration.

Flood disturbance affects morphology and reproduction of woody riparian plants

Riparian forests are structured and maintained by their hydrology. Woody riparian plants typically adapt to the local flood regime to maximise their likelihood of survival and reproductive success. Understanding how extant trees form and reproduce in response to flood disturbance is crucial for predicting vegetation changes and informing restoration. Working in a temperate evergreen riparian forest, we aim to determine whether disturbance-based responses of plants found in other ecosystems also typify woody plants in riparian forests where disturbances are non-lethal, annual events. Using plant surveys and 20-year modelled hydrological data, we examined whether i) the morphology (main stem diameter, height, crown width, crown extent, stem leaning) and ii) reproduction type (sexual and asexual reproduction) and extent of three dominant woody species (Eucalyptus camphora, Leptospermum lanigerum and Melaleuca squarrosa) vary with flood regime (flood frequency and flood duration); and iii) whether different morphology is associated with different reproductive strategies. Increased flooding generally resulted in increased stem numbers and greater stem leaning – morphologies associated with asexual reproduction – of our study species. More frequent flooding also reduced plant size and sexual reproduction in E. camphora. Sexual reproduction in the studied species was more common in taller plants with single, more upright stems in good condition. Flexible morphology and plastic reproductive strategy may constitute an adaptation to mild or chronic disturbance in floodplains. Our findings suggest that woody plants respond to physical disturbance in consistent ways regardless of the nature of the disturbance – be it fires, hurricanes or floods.