Early Events in the Fusarium verticillioides-Maize Interaction Characterized by Using a Green Fluorescent Protein-Expressing Transgenic Isolate

The infection of maize by Fusarium verticillioides can result in highly variable disease symptoms ranging from asymptomatic plants to severe rotting and wilting. We produced F. verticillioides green fluorescent protein-expressing transgenic isolates and used them to characterize early events in the F. verticillioides-maize interaction that may affect later symptom appearance. Plants grown in F. verticillioides-infested soil were smaller and chlorotic. The fungus colonized all of the underground parts of a plant but was found primarily in lateral roots and mesocotyl tissue. In some mesocotyl cells, conidia were produced within 14 to 21 days after infection. Intercellular mycelium was detected, but additional cells were not infected until 21 days after planting. At 25 to 30 days after planting, the mesocotyl and main roots were heavily infected, and rotting developed in these tissues. Other tissues, including the adventitious roots and the stem, appeared to be healthy and contained only a small number of hyphae. These results imply that asymptomatic systemic infection is characterized by a mode of fungal development that includes infection of certain tissues, intercellular growth of a limited number of fungal hyphae, and reproduction of the fungus in a few cells without invasion of other cells. Development of visibly rotted tissue is associated with massive production of fungal mycelium and much less organized growth

Transmission Mode and Assembly of Seed Fungal Endophyte Communities in Wheat and Wheat Wild Relatives

Seeds acquire fungal endophytes either from the environment or from their progenitors. These transmission modes are central in shaping the microbiome because they affect species composition and balance. We studied fungal endophyte communities (FECs) in three plant species: bread wheat (Triticum aestivum), wild emmer wheat (Triticum turgidum dicoccoides), and wild barley (Hordeum spontaneum). We conducted two experiments to test seed-to-seed transmission: (i) we compared FECs in stems and seeds collected from agricultural and natural habitats and (ii) we grew plants under greenhouse conditions to isolate the effect of vertical transmission on the plant FECs. The analysis of seed communities revealed differences in FEC composition and diversity among plant species; however, Alternaria infectoria dominated FECs in all plant species. In field-collected plants, the number of taxa in the seeds was less than half the number in stems, and close to 90% of the seed taxa were found in stems. The FECs from stems and seeds of greenhouse-grown plants were more diverse than the FECs of original seeds; they lacked a single dominant taxon, and the FECs in the new seeds had a similar richness and diversity to stem FECs, with only 40% overlap. The controlled-environment experiment confirmed vertical transmission of certain species but also showed that external infection of the seeds is the main source for specific taxa. Our results show that many taxa can reach the seeds internally, albeit in different abundance, that both infection sources affect seed FEC composition, and that external conditions affect the balance between FECs within the plant

Environmental niche variation and evolutionary diversification of the Brachypodium distachyon grass complex species in their native circum-mediterranean range

© 2015 Botanical Society of America. PREMISE OF THE STUDY: We conducted environmental niche modeling (ENM) of the Brachypodium distachyon s.l. complex, a model group of two diploid annual grasses (B. distachyon, B. stacei) and their derived allotetraploid (B. hybridum), native to the circum-Mediterranean region. We (1) investigated the ENMs of the three species in their native range based on present and past climate data; (2) identified potential overlapping niches of the diploids and their hybrid across four Quaternary windows; (3) tested whether speciation was associated withniche divergence/conservatism in the complex species; and (4) tested for the potential of the polyploid outperforming the diploids in the native range. METHODS: Geo-referenced data, altitude, and 19 climatic variables were used to construct the ENMs. We used paleoclimate niche models to trace the potential existence of ancestral gene flow among the hybridizing species of the complex. KEY RESULTS: Brachypodium distachyon grows in higher, cooler, and wetter places, B. stacei in lower, warmer, and drier places, and B. hybridum in places withintermediate climatic features. Brachypodium hybridum had the largest niche overlap withits parent niches, but a similar distribution range and niche breadth. CONCLUSIONS: Each species had a unique environmental niche though there were multiple niche overlapping areas for the diploids across time, suggesting the potential existence of several hybrid zones during the Pleistocene and the Holocene. No evidence of niche divergence was found, suggesting that species diversification was not driven by ecological speciation but by evolutionary history, though it could be associated to distinct environmental adaptations