Prevalent arbuscular mycorrhizae in roots and highly variable mycobiome in leaves of epiphytic subtropical fern Ophioderma pendulum.

PREMISE: Endophytic and mycorrhizal fungi are crucial in facilitating plant nutrition acquisition and stress tolerance. In epiphytic habitats, plants face nutrition and water stress, but their roots are mostly nonmycorrhizal and especially lacking in arbuscular mycorrhizal associations. Ophioderma pendulum is an epiphytic fern with a partially mycoheterotrophic lifestyle, likely heavily reliant on symbiotic fungi. To characterize fungal associations in the sporophyte of O. pendulum, we focused on leaves and roots of O. pendulum, seeking to reveal the fungal communities in these organs. METHODS: Roots and leaves from O. pendulum in a subtropical forest were examined microscopically to observe the morphology of fungal structures and determine the percentage of various fungal structures in host tissues. Fungal composition was profiled using metabarcoding techniques that targeted ITS2 of the nuclear ribosomal DNA. RESULTS: Roots were consistently colonized by arbuscular mycorrhizal fungi (Glomeromycota), especially Acaulospora. Unlike previous findings on epiphytic ferns, dark septate endophytes were rare in O. pendulum roots. Leaves were predominantly colonized by Ascomycota fungi, specifically the classes Dothideomycetes (46.88%), Eurotiomycetes (11.51%), Sordariomycetes (6.23%), and Leotiomycetes (6.14%). Across sampling sites, fungal community compositions were similar in the roots but differed significantly in the leaves. CONCLUSIONS: Ophioderma pendulum maintains stable, single-taxon-dominant communities in the roots, primarily featuring arbuscular mycorrhizal fungi, whereas the leaves may harbor opportunistic fungal colonizers. Our study underlines the significance of mycorrhizal fungi in the adaptation of epiphytic ferns.

Dense infraspecific sampling reveals rapid and independent trajectories of plastome degradation in a heterotrophic orchid complex.

Heterotrophic plants provide excellent opportunities to study the effects of altered selective regimes on genome evolution. Plastid genome (plastome) studies in heterotrophic plants are often based on one or a few highly divergent species or sequences as representatives of an entire lineage, thus missing important evolutionary-transitory events. Here, we present the first infraspecific analysis of plastome evolution in any heterotrophic plant. By combining genome skimming and targeted sequence capture, we address hypotheses on the degree and rate of plastome degradation in a complex of leafless orchids (Corallorhiza striata) across its geographic range. Plastomes provide strong support for relationships and evidence of reciprocal monophyly between C. involuta and the endangered C. bentleyi. Plastome degradation is extensive, occurring rapidly over a few million years, with evidence of differing rates of genomic change among the two principal clades of the complex. Genome skimming and targeted sequence capture differ widely in coverage depth overall, with depth in targeted sequence capture datasets varying immensely across the plastome as a function of GC content. These findings will help to fill a knowledge gap in models of heterotrophic plastid genome evolution, and have implications for future studies in heterotrophs.

A phosphorus threshold for mycoheterotrophic plants in tropical forests.

The majority of terrestrial plants associate with arbuscular mycorrhizal (AM) fungi, which typically facilitate the uptake of limiting mineral nutrients by plants in exchange for plant carbon. However, hundreds of non-photosynthetic plant species-mycoheterotrophs-depend entirely on AM fungi for carbon as well as mineral nutrition. Mycoheterotrophs can provide insight into the operation and regulation of AM fungal relationships, but little is known about the factors, fungal or otherwise, that affect mycoheterotroph abundance and distribution. In a lowland tropical forest in Panama, we conducted the first systematic investigation into the influence of abiotic factors on the abundance and distribution of mycoheterotrophs, to ask whether the availability of nitrogen and phosphorus altered the occurrence of mycoheterotrophs and their AM fungal partners. Across a natural fertility gradient spanning the isthmus of Panama, and also in a long-term nutrient-addition experiment, mycoheterotrophs were entirely absent when soil exchangeable phosphate concentrations exceeded 2 mg P kg-1 Experimental phosphorus addition reduced the abundance of AM fungi, and also reduced the abundance of the specific AM fungal taxa required by the mycoheterotrophs, suggesting that the phosphorus sensitivity of mycoheterotrophs is underpinned by the phosphorus sensitivity of their AM fungal hosts. The soil phosphorus concentration of 2 mg P kg-1 also corresponds to a marked shift in tree community composition and soil phosphatase activity across the fertility gradient, suggesting that our findings have broad ecological significance.

[Identification and expression analysis of receptor-like kinase gene ERECTA in mycoheterotrophic plant Monotropa hypopitys].

The precise spatial-temporal coordination of cell division and differentiation is necessary for the correct formation of tissues, organs, and the organism as a whole. This coordination has been implemented by the intercellular communication mediated by signaling molecules and receptors that selectively recognize them. Membrane receptor kinases of ERECTA family regulate inflorescence and flower structure, the formation of root epidermis and adaptation responses. The characterization of the ERECTA genes of flowering plant pinesap Monotropa hypopitys with unique development features can enrich the knowledge about the kinase ERECTA functions and conserved development processes with their participation. Transcriptomic and genomic search with the subsequent structural-phylogenetic analysis identified the mRNA of a gene of serine-threonine kinase receptor with leucine-rich repeats of MhyERL1, which is the only ortholog of the ERECTA family kinases of pinesap. A quantitative analysis of the MhyERL1 gene transcripts has revealed its expression in all analyzed pinesap tissues with maximum levels in the flowers. MhyERL1 is probably involved in defining the inflorescence and flower architecture, and the formation of the pinesap root epidermis. The cascades involving ERL1 are apparently conserved. The exception are pathways associated with the development of above-ground vegetative structures, and the immune response to fungal pathogens probably lost in the process of the pinesap adaptation to unfavorable environmental conditions.

Understanding the evolution of holoparasitic plants: the complete plastid genome of the holoparasite Cytinus hypocistis (Cytinaceae).

Background and Aims Plant plastid genomes are highly conserved in size, gene content and structure; however, parasitic plants are a noticeable exception to this evolutionary stability. Although the evolution of parasites could help to better understand plastome evolution in general, complete plastomes of parasites have been sequenced only for some lineages so far. Here we contribute to filling this gap by providing and analysing the complete plastome sequence of Cytinus hypocistis, the first parasite sequenced for Malvales and a species suspected to have an extremely small genome. Methods We sequenced and assembled de novo the plastid genome of Cytinus hypocistis using a shotgun approach on genomic DNA. Phylogenomic analyses based on coding regions were performed on Malvidae. For each coding region present in Cytinus, we tested for relaxation or intensification of selective pressures in the Cytinus lineage compared with autotrophic Malvales. Key Results Cytinus hypocistis has an extremely divergent genome that is among the smallest sequenced to date (19·4 kb), with only 23 genes and no inverted repeat regions. Phylogenomic analysis confirmed the position of Cytinus within Malvales. All coding regions of Cytinus plastome presented very high substitution rates compared with non-parasitic Malvales. Conclusions Some regions were inferred to be under relaxed negative selection in Cytinus, suggesting that further plastome reduction is occurring due to relaxed purifying selection associated with the loss of photosynthetic activity. On the other hand, increased selection intensity and strong positive selection were detected for rpl22 in the Cytinus lineage, which might indicate an evolutionary role in the host-parasite arms race, a point that needs further research.

The Role of Mycorrhizal Fungi in Orchids Mycobiont and Orchids.

BACKGROUND: In nature, orchid plants are obligate myco-heterotrophs, and rely on mycorrhizal nutrient resources to grow and sustain in the wild, until they become physiologically active photosynthetic plants. Their seeds lack nutrient reserves and receive the necessary carbon from symbiotic fungi during germination. A mycorrhizal fungus provides nutrients, especially sugars, as well as water to the corresponding host plant. The range and distribution of orchid mycorrhizal fungi influence the survivability of orchid populations in their natural habitats. Mycorrhizae form symbiotic connections with the parenchymatous tissues of the roots of orchid plants. OBJECTIVE: The objective of this study was to examine the presence of mycorrhiza in the roots of Aerides multiflora during the vegetative phase Methods: Fresh roots were hand-sectioned, and thin sections were observed under the microscope to locate the presence of mycorrhiza. Simultaneously, to observe the expansion of mycorrhiza in the cortical region. RESULTS: During the vegetative phase of plant growth, a peloton-like structure forms within the cortical region of the orchid roots. Mycorrhizae was observed to be distributed throughout the cortical layer of the root. CONCLUSION: This communication reviews the role of mycorrhiza in orchid plants.

Gymnosiphon syceorosensis (Burmanniaceae), the second new species for the Philippines.

A new holomycoheterotrophic member of Burmanniaceae, Gymnosiphon syceorosensis, is described from Mt. Hamiguitan located on the island of Mindanao, Philippines. This species differs from the recently named G. philippinensis from Cebu in a number of quantitative and qualitative characters. Phenetic (neighbor-joining) and phylogenetic (maximum parsimony) analyses of characters from Asian and Australian Gymnosiphon species were conducted and diagnostic taxonomic features were discussed. This new species appears to be most closely related to G. affinis J.J. Sm. from New Guinea but differs in a number of floral features including inner perianth lobe shape, stamen position in floral tube, and anther connective shape.

Epitypification with an emended description of Tropidia connata (Orchidaceae, Epidendroideae, Tropidieae).

We found several specimens of Tropidia connata, a mycoheterotrophic orchid from Borneo, with features which have never been described in any of the existing literature, namely subterranean tubers. We mainly focus on the importance of the subterranean structures in comparison with the mycoheterotrophic genus Kalimantanorchis from the tribe Tropidieae. This finding of the tuberous structure gives a new insight into the classification of mycoheterotrohic species of Tropidieae and might affect the generic placement of Kalimantanorchis. We made a detailed study on the newly discovered specimens as well as the type, and found more diagnostic characters of T. connata than the previous description. Considering that the type specimen lacks the whole tuberous character, we consequently designate an epitype with a drawing and emend the description.

Symbiotic germination and development of myco-heterotrophic plants in nature: ontogeny of Corallorhiza trifida and characterization of its mycorrhizal fungi.

The processes of symbiotic germination and seedling development were analysed in the myco-heterotrophic orchid Corallorhiza trifida, seeds of which were buried in 'packets' either adjacent to or at varying distances from adult plants in defined communities of ectomycorrhizal tree species. Germination occurred within eight months of burial under Betula-Alnus and within seven months under Salix repens. It was always associated with penetration of the suspensor by a clamp-forming mycorrhizal fungus. Four distinct developmental stages were defined and the rates of transition through these stages were plotted. There was no evidence of a relationship between extent of germination or rate of development and the presence of naturally distributed plants of C. trifida at the spatial scale of 1 m. The best germination and the most rapid rate of development of C. trifida seedlings occurred in a Salix repens community located at a considerable distance from any extant C. trifida population. Determination of internal transcribed spacer (ITS) RFLPs and of gene sequences of the fungi involved in symbiotic germination and growth of C. trifida, revealed them to belong exclusively to the Thelephora-Tomentella complex of the Thelephoraceae. These fungi are known also to be ectomycorrhizal associates of trees. It is hypothesized that the rate of growth of the C. trifida seedlings is determined by the ability of the fungal symbionts to transfer carbon from their ectomycorrhizal co-associates.

Characterization of microsatellite markers for pinedrops, Pterospora andromedea (Ericaceae), from Illumina MiSeq sequencing.

PREMISE OF THE STUDY: Pterospora andromedea (Ericaceae) is a mycoheterotrophic plant endemic to North America with a disjunct distribution. Eastern populations are in decline compared to western populations. Microsatellite loci will allow comparison of genetic diversity in endangered to nonthreatened populations. • METHODS AND RESULTS: Illumina MiSeq sequencing resulted in development of 12 polymorphic microsatellite loci from 63 perfect microsatellite loci tested. One polymorphic locus was obtained from a traditional enrichment method. These 13 loci were screened across two western and two eastern populations. For western and eastern populations, respectively, number of alleles ranged from one to 10 and one to four, and observed heterozygosity ranged from 0.000 to 0.389 and 0.000 to 0.143. • CONCLUSIONS: These are the first microsatellite loci developed for Pterospora. They will be useful in conservation efforts of the eastern populations and for examination of population genetic parameters at different geographic scales and comparison with mycorrhizal fungal hosts.