Pistil Smut Infection Increases Ovary Production, Seed Yield Components, and Pseudosexual Reproductive Allocation in Buffalograss

The genome of Salmacisia buchloëana, the parasitic puppet master pulling strings of sexual phenotypic monstrosities in buffalograss

To complete its parasitic lifecycle, Salmacisia buchloëana, a biotrophic fungus, manipulates reproductive organ development, meristem determinacy, and resource allocation in its dioecious plant host, buffalograss (Bouteloua dactyloides; Poaceae). To gain insight into S. buchloëana's ability to manipulate its host, we sequenced and assembled the 20.1 Mb genome of S. buchloëana into 22 chromosome-level pseudomolecules. Phylogenetic analysis suggests that S. buchloëana is nested within the genus Tilletia and diverged from Tilletia caries and Tilletia walkeri ∼40 MYA. We find that S. buchloëana contains a novel chromosome arm with no syntenic relationship to other publicly available Tilletia genomes, and that genes on the novel arm are upregulated upon infection, suggesting that this unique chromosomal segment may have played a critical role in S. buchloëana's evolution and host specificity. Salmacisia buchloëana has one of the largest fractions of serine peptidases (1.53% of the proteome) and one of the highest GC contents (62.3%) in all classified fungi. Analysis of codon base composition indicated that GC content is controlled more by selective constraints than directional mutation, and that S. buchloëana has a unique bias for the serine codon UCG. Finally, we identify 3 inteins within the S. buchloëana genome, 2 of which are located in a gene often used in fungal taxonomy. The genomic and transcriptomic resources generated here will aid plant pathologists and breeders by providing insight into the extracellular components contributing to sex determination in dioecious grasses.

Stigmas of holoparasitic Phelipanche arenaria (Orobanchaceae) - a suitable ephemeric flower habitat for development unique microbiome

BACKGROUND

Microbial communities have occasionally been observed in part of the ephemeric reproductive structure of floral stigmas, but their prevalence, phylogenetic diversity and ecological roles are understudied. This report describes the first study of bacterial and fungal communities in immature and mature stigma tissue of the endangered holoparasitic plant Phelipanche arenaria. Culture-dependent methods coupled with next-generation sequencing indicated that a small surface of the flower stigma was an unexpectedly rich and diverse microhabitat for colonization of microbial. We also compared the enzymatic activity of the bacterial communities between immature and mature stigmas samples.

RESULTS

Using high-throughput sequencing methods, we identified and classified 39 to over 51 OTUs per sample for bacterial OTUs represented by Pantoea agglomerans and P. ananatis, comprising 50.6%, followed by Pseudomonas, Luteibacter spp., Sphingomonas spp. with 17% of total frequency. The bacterial profile of immature stigmas of P. arenaria contained unique microorganisms (21 of the most numerous OTUs) that were not confirmed in mature stigmas. However, the enzymatic activity of bacteria in mature stigmas of P. arenaria showed more activity than observed in immature stigmas. In the fungal profile, we recorded even 80 OTUs in mature stigmas, consisting of Capnodiales 45.03% of the total abundance with 28.27% of frequency was created by Alternaria eichhorniae (10.55%), Mycosphaerella tassiana (9.69%), and Aureobasidium pullulans (8.03%). Additionally, numerous putative plant growth-promoting bacteria, fungal pathogens and pathogen-antagonistic yeasts were also detected.

CONCLUSIONS

Our study uncovered that P. arenaria stigmas host diverse bacterial and fungal communities. These microorganisms are well known and have been described as beneficial for biotechnological and environmental applications (e.g., production of different enzymes and antimicrobial compounds). This research provided valuable insight into the parasitic plant-microbe interactions.

Interspecies and temporal dynamics of bacterial and fungal microbiomes of pistil stigmas in flowers in holoparasitic plants of the Orobanche series Alsaticae (Orobanchaceae)

Little is known about the microbiomes of flower parts, and even less information is available regarding these microorganisms' colonization of specific niches in parasitic plants. We investigate the temporal interspecies dynamics of the parasitic plants microbiome of flower stigmas in two stages of development: immature stigmas in flower buds and mature stigmas in opened flowers. We compared two related holoparasitic Orobanche species from localities approximately 90 km apart and characterize their bacterial and fungal communities using 16S rRNA gene and ITS sequences, respectively. We identified from 127 to over 228 OTUs per sample for fungi, sequences belonging to genera: Aureobasidium, Cladosporium, Malassezia, Mycosphaerella, and Pleosporales, constituting approximately 53% of the community in total. In the bacterial profile, we recorded 40 to over 68 OTUs per sample consisting of Enterobacteriaceae, and genera Cellulosimicrobium, Pantoea, and Pseudomonas spp., with an approximately 75% frequency. In microbial communities, higher numbers of OTUs colonizing mature stigmas were recorded than in immature. This implies that the dynamics and concurrence of microbial communities were different between O. alsatica and O. bartlingii and underwent significant changes during flower development. To the best of our knowledge, is the first study of the interspecies and temporal dynamics of the bacterial and fungal microbiomes of pistil stigmas in flowers.

Draft Genome Sequence of Salmacisia buchloëana (Basidiomycota), Which Induces Hermaphroditism in Dioecious Buffalograss

Here, we report the draft genome of Salmacisia buchloëana type strain OK1, a monotypic species of fungi that induces ovary development in genetic male plants and increases reproductive biomass allocation in its host buffalograss. This research will enhance our understanding of fungal manipulation of host development at the genomic level.

Female Salix viminalis are more severely infected by Melampsora spp. but neither sex experiences associational effects

Associational effects of plant genotype or species on plant biotic interactions are common, not least for disease spread, but associational effects of plant sex on interactions have largely been ignored. Sex in dioecious plants can affect biotic interactions with herbivores and pollinators; however, its effects on plant-pathogen interactions are understudied and associational effects are unknown. In a replicated field experiment, we assessed Melampsora spp. leaf rust infection in monosexual and mixed sex plots of dioecious Salix viminalis L. to determine whether plant sex has either direct or associational effects on infection severity. We found no differences in Melampsora spp. infection severity among sexual monocultures and mixtures in our field experiment. However, female plants were overall more severely infected. In addition, we surveyed previous studies of infection in S. viminalis clones and reevaluated the studies after we assigned sex to the clones. We found that females were generally more severely infected, as in our field study. Similarly, in a survey of studies on sex-biased infection in dioecious plants, we found more female-biased infections in plant-pathogen pairs. We conclude that there was no evidence for associational plant sex effects of neighboring conspecifics for either females or males on infection severity. Instead, plant sex effects on infection act at an individual plant level. Our findings also suggest that female plants may in general be more severely affected by fungal pathogens than males.