Stationary phase development of Trimmatostroma abietis

Exploring fungus-plant N transfer in a tripartite ant-plant-fungus mutualism

BACKGROUND AND AIMS

The plant Hirtella physophora, the ant Allomerus decemarticulatus and a fungus, Trimmatostroma sp., form a tripartite association. The ants manipulate both the plant trichomes and the fungus to build galleries under the stems of their host plant used to capture prey. In addition to its structural role, the fungus also improves nutrient uptake by the host plant. But it still remains unclear whether the fungus plays an indirect or a direct role in transferring nutrients to the plant. This study aimed to trace the transfer of N from the fungus to the plant's stem tissue.

METHODS

Optical microscopy and transmission electron microscopy (TEM) were used to investigate the presence of fungal hyphae in the stem tissues. Then, a 15N-labelling experiment was combined with a nanoscale secondary-ion mass spectrometry (NanoSIMS 50) isotopic imaging approach to trace the movement of added 15N from the fungus to plant tissues.

KEY RESULTS

The TEM images clearly showed hyphae inside the stem tissue in the cellular compartment. Also, fungal hyphae were seen perforating the wall of the parenchyma cell. The 15N provisioning of the fungus in the galleries resulted in significant enrichment of the 15N signature of the plant's leaves 1 d after the 15N-labelling solution was deposited on the fungus-bearing trap. Finally, NanoSIMS imaging proved that nitrogen was transferred biotrophically from the fungus to the stem tissue.

CONCLUSIONS

This study provides evidence that the fungi are connected endophytically to an ant-plant system and actively transfer nitrogen from 15N-labelling solution to the plant's stem tissues. Overall, this study underlines how complex the trophic structure of ant-plant interactions is due to the presence of the fungus and provides insight into the possibly important nutritional aspects and tradeoffs involved in myrmecophyte-ant mutualisms.

Drought meets acid: three new genera in a dothidealean clade of extremotolerant fungi

Fungal strains isolated from rocks and lichens collected in the Antarctic ice-free area of the Victoria Land, one of the coldest and driest habitats on earth, were found in two phylogenetically isolated positions within the subclass Dothideomycetidae. They are here reported as new genera and species, Recurvomyces mirabilisgen. nov., sp. nov. and Elasticomyces elasticusgen. nov., sp. nov. The nearest neighbours within the clades were other rock-inhabiting fungi from dry environments, either cold or hot. Plant-associated Mycosphaerella-like species, known as invaders of leathery leaves in semi-arid climates, are also phylogenetically related with the new taxa. The clusters are also related to the halophilic species Hortaea werneckii, as well as to acidophilic fungi. One of the latter, able to grow at pH 0, is Scytalidium acidophilum, which is ascribed here to the newly validated genus Acidomyces. The ecological implications of this finding are discussed.

Pleomorphic conidiogenesis among strains of Knufia cryptophialidica

Pleomorphic conidiogenesis was examined in four strains of Knufia cryptophialidica Hutchison & Untereiner in culture. The ex-type strain (DAOM 216555) was the most plastic, exhibiting various patterns of conidiogenesis, and was the only strain that produced phialides, that is, the most important diagnostic structure of the genus, although many of these phialides were aberrant and produced abnormally swollen conidia that appeared to lack cytoplasm. Subsequently, hyphae emerged from the aberrant phialides and some of these hyphae later disarticulated to form thallic-arthric conidia. The ex-type strain ceased to produce normal phialides after several serial transfers onto malt extract agar. Endoconidiogenesis in K. cryptophialidica, reported here for the first time, involved subdivision of conidiogenous cells by septation and schizolysis through the septa, and their release was by rupture and subsequent degeneration of the conidiogenous cell wall. Both thallic-arthric and endogenous conidia occurred in all strains and may serve as more reliable diagnostic characters of K. cryptophialidica than phialidic conidia.Key words: black meristematic fungus, endoconidia, phialides.

Hortaea acidophila, a new acid-tolerant black yeast from lignite

A hitherto undescribed black yeast was isolated from an extract of brown coal containing humic and fulvic acids at pH 0.6. The fungus showed morphological similarity to some members of the genus Exophiala (Chaetothyriales) and of Hortaea (Dothideales). Based on SSU rDNA sequence similarity to meristematic members of the Dothideales, the new species was accommodated in Hortaea, which presently contains only a single, halophilic species, H. werneckii.