10 research outputs found
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Plant compartment and genetic variation drive microbiome composition in switchgrass roots.
Switchgrass (Panicum virgatum) is a promising biofuel crop native to the United States with genotypes that are adapted to a wide range of distinct ecosystems. Various plants have been shown to undergo symbioses with plant growth-promoting bacteria and fungi, however, plant-associated microbial communities of switchgrass have not been extensively studied to date. We present 16S ribosomal RNA gene and internal transcribed spacer (ITS) data of rhizosphere and root endosphere compartments of four switchgrass genotypes to test the hypothesis that host selection of its root microbiota prevails after transfer to non-native soil. We show that differences in bacterial, archaeal and fungal community composition and diversity are strongly driven by plant compartment and switchgrass genotypes and ecotypes. Plant-associated microbiota show an enrichment in Alphaproteobacteria and Actinobacteria as well as Sordariales and Pleosporales compared with the surrounding soil. Root associated compartments display low-complexity communities dominated and enriched in Actinobacteria, in particular Streptomyces, in the lowland genotypes, and in Alphaproteobacteria, specifically Sphingobium, in the upland genotypes. Our comprehensive root analysis serves as a snapshot of host-specific bacterial and fungal associations of switchgrass in the field and confirms that host-selected microbiomes persist after transfer to non-native soil
A Morphometric Analysis of Arceuthobium campylopodum and Arceuthobium divaricatum (Viscaceae)
Although the classification of pinyon dwarf mistletoe (Arceuthobium divaricatum, Viscaceae) has not been controversial to any extent since Engelmann described it in 1878, a recent taxonomic treatment has included this species in western dwarf mistletoe (A. campylopodum). While pinyon dwarf mistletoe is only known to parasitize pinyon pines (Pinus subsection Cembroides), western dwarf mistletoe as it has been known since the late 1800s is a principal parasite of Pinus ponderosa and P. jeffreyi and has never been observed parasitizing pinyon pines. With reservations about the recent classification of pinyon dwarf mistletoe and its treatment under A. campylopodum, we undertook this study to examine in detail the morphological characteristics of pinyon dwarf mistletoe and compare them with those of western dwarf mistletoe. Pinyon and western dwarf mistletoe populations were sampled throughout most of their geographic ranges and morphological traits including plant, flower, fruit, and seed dimensions were measured. Thereafter, we compared morphological characteristics between A. campylopodum and A. divaricatum using univariate and multivariate statistics to determine significant differences among morphologies of both male and female plants. Our analyses clearly demonstrated that pinyon and western dwarf mistletoe are morphologically distinct as originally proposed by G. Engelmann in the late 19th century. Furthermore, the host affinities of the two taxa clearly distinguish them from each other. Therefore, we recommend that A. campylopodum and A. divaricatum continue to be classified as separate species. Morphological differences between these species are summarized and a key is provided for use in their field identification
The evaluation of virulent and hypovirulent inocula of the chestnut blight fungus, Cryphonectria parasitica, to incite infection and spermatize virulent cankers.
Transgenic hypovirulent (HV) strains of Cryphonectria parasitica [Murrill] M.E. Barr engineered to contain an infectious cDNA copy of Cryphonectria hypovirus 1 (Hypoviridae; CHV1) may provide an efficient mechanism to introduce hypoviruses into genetically heterogeneous populations of the chestnut blight fungus. However, elucidating the factors that affect the infection of chestnut and spread of C. parasitica is needed to fully utilize the potential of transgenic HV strains for the biological control of chestnut blight. In one study, three experiments were conducted at a forested site near Bartow, West Virginia. The seasonality of HV and virulent canker development was measured in the first experiment by inoculating healthy chestnut trees at 8-wk intervals (May, July, September) with cytoplasmic HV (EP146/tpTE7), transgenic HV (EP146/pXHE7), or virulent (EP146) inoculum. The cytoplasmic and transgenic HV isolates were significantly less able to infect and grow in chestnut bark when compared to the virulent isolate. Inoculations made with virulent conidia or mycelium resulted in more infections and larger cankers after 1-yr than those made with conidia or mycelium of the two HV isolates. Virulent inoculations initiated in May incited the greatest amount of disease (i.e., infection and canker growth) after 1-yr followed by September and July inoculations. A similar seasonal pattern of infection was observed for cytoplasmic HV inocula, but when infection occurred, the growth of cytoplasmic HV cankers was not affected by month of inoculation. The frequency of infection and canker growth for the transgenic HV isolate exhibited little seasonal variation as described above except inoculations were made with either 300 or 3,000 conidia or ascospores per wound. Inoculum concentration had no effect on the incidence of infection or canker growth for either the cytoplasmic or transgenic HV isolate after seven months. In contrast, inoculations using 3,000 virulent conidia significantly increased the frequency of infection compared to those made with 300 virulent conidia. The third experiment examined the effect(s) of inoculum formulation, delivery substrate, and wound-size the development of virulent and transgenic HV cankers. Inoculations using virulent conidia in agar (potato dextrose agar [PDA] or 2.5% water agar) and a wound diameter of nine mm resulted in the greatest incidence of infection after seven months when compared to inoculations using virulent ascospores or an agar suspension containing mycelia and conidia. Transgenic HV inoculations with a nine mm wound and a mycelium-conidia agar suspension produced the largest number of cankers compared to transgenic HV inoculations initiated in the first two experiments and were as effective as virulent inoculations with nine mm wounds. Because the fungal propagule responsible for fertilizing the female thallus of C. parasitica in the sexual cycle has yet to be identified, a second study was conducted to determine whether ascospores, conidia, or mycelial fragments function as spermatia. Brown-pigmented cytoplasmic (EP146/tpTE7) and transgenic HV (EP146/pXHE7) and virulent (EP146) isolates were used for in situ spermatization of a virulent orange-pigmented isolate (EP155) pre-established as cankers on healthy chestnuts at the forested site described above. The formation of brown and orange ascospores (∼1:1) in new perithecia was the marker for successful spermatization. Over a two-year period, cytoplasmic and transgenic HV and virulent conidia of C. parasitica were the only propagules to successfully spermatized virulent cankers. When virulent or cytoplasmic HV conidia were used as spermatia, ascospore progeny were hypovirus-free. However, ascospores resulting from crosses involving transgenic HV conidia were hypovirus-infected and resistant to hygromycin, thereby indicating the successful inheritance of the CHV1 transgene in these progeny
A Morphometric Analysis Of Dwarf Mistletoes In The Arceuthobium campylopodum – occidentale Complex (Viscaceae)
Volume: 62Start Page: 1End Page: 2
Association of ergot alkaloids with conidiation in \u3ci\u3eAspergillus fumigatus\u3c/i\u3e
Ergot alkaloids are mycotoxins that affect the nervous and reproductive systems of exposed individuals through interactions with monoamine receptors. They have been studied more widely in ergot fungi and grass endophytes but also are found in Aspergillus fumigatus, an opportunistic human pathogen that reproduces and disseminates exclusively through conidia. The ergot alkaloids festuclavine and fumigaclavines A, B and C are present in or on conidia of A. fumigatus. Cultures of the fungus that are free of conidia are difficult to obtain, obscuring comparisons of conidia versus vegetative hyphae as sources of the ergot alkaloids. To create conidiation-deficient strains of A. fumigatus we manipulated the bristle A gene (brlA), which controls vesicle formation or budding growth necessary for conidiation in Aspergillus spp. Disruption of brlA in A. fumigatus, via homologous recombination, resulted in a nonconidiating mutant that produced bristle-like structures instead of conidiophores and conidia. Moreover the disrupted strain failed to produce ergot alkaloids as verified by HPLC analyses. Complementation with a wild-type allele restored conidiation and ergot alkaloid production. These results suggest that ergot alkaloids are not produced within the vegetative mycelium of the fungus and are associated directly with conidiation
DISTRIBUTION AND MORPHOLOGICAL CHARACTERISTICS OF ARCEUTHOBIUM HONDURENSE AND A. NIGRUM (VISCACEAE) IN MEXICO
Volume: 6Start Page: 599End Page: 60
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Plant compartment and genetic variation drive microbiome composition in switchgrass roots.
Switchgrass (Panicum virgatum) is a promising biofuel crop native to the United States with genotypes that are adapted to a wide range of distinct ecosystems. Various plants have been shown to undergo symbioses with plant growth-promoting bacteria and fungi, however, plant-associated microbial communities of switchgrass have not been extensively studied to date. We present 16S ribosomal RNA gene and internal transcribed spacer (ITS) data of rhizosphere and root endosphere compartments of four switchgrass genotypes to test the hypothesis that host selection of its root microbiota prevails after transfer to non-native soil. We show that differences in bacterial, archaeal and fungal community composition and diversity are strongly driven by plant compartment and switchgrass genotypes and ecotypes. Plant-associated microbiota show an enrichment in Alphaproteobacteria and Actinobacteria as well as Sordariales and Pleosporales compared with the surrounding soil. Root associated compartments display low-complexity communities dominated and enriched in Actinobacteria, in particular Streptomyces, in the lowland genotypes, and in Alphaproteobacteria, specifically Sphingobium, in the upland genotypes. Our comprehensive root analysis serves as a snapshot of host-specific bacterial and fungal associations of switchgrass in the field and confirms that host-selected microbiomes persist after transfer to non-native soil