Showing papers on "Epichloë published in 2012"

SOLiD-SAGE of Endophyte-Infected Red Fescue Reveals Numerous Effects on Host Transcriptome and an Abundance of Highly Expressed Fungal Secreted Proteins

Abstract: One of the most important plant-fungal symbiotic relationships is that of cool season grasses with endophytic fungi of the genera Epichloe and Neotyphodium These associations often confer benefits, such as resistance to herbivores and improved drought tolerance, to the hosts One benefit that appears to be unique to fine fescue grasses is disease resistance As a first step towards understanding the basis of the endophyte-mediated disease resistance in Festuca rubra we carried out a SOLiD-SAGE quantitative transcriptome comparison of endophyte-free and Epichloe festucae-infected F rubra Over 200 plant genes involved in a wide variety of physiological processes were statistically significantly differentially expressed between the two samples Many of the endophyte expressed genes were surprisingly abundant, with the most abundant fungal tag representing over 10% of the fungal mapped tags Many of the abundant fungal tags were for secreted proteins The second most abundantly expressed fungal gene was for a secreted antifungal protein and is of particular interest regarding the endophyte-mediated disease resistance Similar genes in Penicillium and Aspergillus spp have been demonstrated to have antifungal activity Of the 10 epichloae whole genome sequences available, only one isolate of E festucae and Neotyphodium gansuense var inebrians have an antifungal protein gene The uniqueness of this gene in E festucae from F rubra, its transcript abundance, and the secreted nature of the protein, all suggest it may be involved in the disease resistance conferred to the host, which is a unique feature of the fine fescue–endophyte symbiosis

Genetic diversity in epichloid endophytes of Hordelymus europaeus suggests repeated host jumps and interspecific hybridizations.

Abstract: Epichloid fungal endophytes (Epichloe and Neotyphodium spp.) are excellent model systems for studying speciation processes because of their variable life history traits that are linked to host grass fitness. Presumed jumps to new hosts and subsequent somatic hybridizations appear to be common among epichloid endophytes resulting in increased genetic variation upon which selection can act and speciation be initiated. In this study, we explored the endophyte diversity of a rare European native woodland grass species, Hordelymus europaeus, along a latitudinal transect covering the entire distribution range of H. europaeus. From 28 populations in six countries, isolates were sampled and molecularly characterized. Based on the sequences of tubB and tefA, six distinct epichloid taxa (interspecific hybrid or cryptic haploid species) were found, of which four were novel and two have been previously reported from this host. Of the novel endophytes, two were presumed to be interspecific hybrids and two of nonhybrid origin. While previously known endophytes of H. europaeus are seed-born and strictly asexual, one of the novel nonhybrid endophytes found in the glacial refugium of the Apennine peninsula reproduced sexually in cultured plants. This is the first case of a seed-borne, but sexually reproducing endophyte of this host. We discuss the origin, and possible ancestral species, of the six epichloid taxa using phylogenetic analyses. Repeated host jumps and somatic hybridizations characterize the diversity of the endophytes. To date, no other grass species is known to host a larger diversity of endophytes than H. europaeus.

Population studies of native grass-endophyte symbioses provide clues for the roles of host jumps and hybridization in driving their evolution.

Abstract: Fungal endophytes in the genera Epichloe and Neotyphodium, collectively termed the epichloae, have fascinated biologists for decades. These intriguing fungi, also referred to as ‘class 1 or clavicipitaceous endophytes’, spend the large majority, or even their entire life cycle, within the tissues of their cool-season grass hosts without eliciting any symptoms of infection. While all epichloae reside within the intercellular spaces of aboveground vegetative grass tissues, the species at the symbiotic extreme are known as Neotyphodium, and the intimacy of their interaction extends to the reproductive (flowering) stage. At this point, fungal filaments (hyphae) nondestructively invade the developing ovaries of their host and are incorporated into perfectly viable, healthy seeds. Thus, these endophytes live solely within the tissues of their host plants and are transmitted maternally from generation to generation. A second life history characteristic of interest is that while all Epichloe and some Neotyphodium species are haploid, a great many of the strictly seed-transmitted Neotyphodium spp. are interspecific hybrids. This phenomenon may be critical for the success of these symbioses over longer spans of evolutionary time and will be discussed in greater detail below. A third characteristic, and one of the primary reasons these grass endophytes have received so much attention over the last three decades, is the strong mutualistic nature these relationships often exhibit. In exchange for photosynthetically derived carbon, the endophytes protect their cool-season grass hosts from grazing herbivores and a variety of abiotic stresses. It has been hypothesized that these three biological phenomena are related (Schardl & Craven 2003), perhaps with the former two driving the third, and it is here that the recent article in Molecular Ecology entitled ‘Genetic diversity in epichloid endophytes of Hordelymus europaeus suggests repeated host jumps and interspecific hybridizations’, by Oberhofer & Leuchtmann (2012), provides critical clues to linking these traits together. While the large majority of studies have focused on documenting the ever-increasing list of mutualistic qualities attributed to these fungi, very few have taken an exhaustive population-level approach to document plant and endophyte genotypes within a naturally occurring system (Faeth et al. 2010; Jani et al. 2010; Tintjer & Rudgers 2006). Such information is crucial to more fully elucidate the factors shaping grass-endophyte symbioses and those often driving these relationships to mutualistic extremes.

Positive association between Neotyphodium endophytes and arbuscular mycorrhizal fungi: a widespread trait in native grasses.

Abstract: The effect of epichloe endophytes on the symbiosis between Arbuscular mycorrhizal fungi (AMF) and wild native grasses was studied in Neotyphodium-infected (E+) and uninfected (E-) plants in natural populations of Bromus setifolius and Poa bonariensis, and in a field experiment with B. auleticus. In vitro assays were carried out in order to study the effect of four strains of Neotyphodium, isolated from B. setifolius, on pre-infective stages of two species of AMF: Gigaspora margarita and G. rosea. The AMF colonization was significantly higher in E+ populations than in Epopulations for all three hosts. No significant differences were detected between E+ and Eplants when they coexisted in the same population. In vitro assays revealed that exudates from endophyte strains significantly enhanced hyphal length and the number of hyphal branches in AMF. Our results suggest that the positive effect of Neotyphodium endophytes on AMF is a widespread phenomenon in native grasses.