Deciphering Molecular Host-Pathogen Interactions During Ramularia Collo-Cygni Infection on Barley.

Ramularia collo-cygni is the causal agent of Ramularia leaf spot disease (RLS) on barley and became, during the recent decades, an increasing threat for farmers across the world. Here, we analyze morphological, transcriptional, and metabolic responses of two barley cultivars having contrasting tolerance to RLS, when infected by an aggressive or mild R. collo-cygni isolate. We found that fungal biomass in leaves of the two cultivars does not correlate with their tolerance to RLS, and both cultivars displayed cell wall reinforcement at the point of contact with the fungal hyphae. Comparative transcriptome analysis identified that the largest transcriptional differences between cultivars are at the early stages of fungal colonization with differential expression of kinases, calmodulins, and defense proteins. Weighted gene co-expression network analysis identified modules of co-expressed genes, and hub genes important for cultivar responses to the two R. collo-cygni isolates. Metabolite analyses of the same leaves identified defense compounds such as p-CHDA and serotonin, correlating with responses observed at transcriptome and morphological level. Together these all-round responses of barley to R. collo-cygni provide molecular tools for further development of genetic and physiological markers that may be tested for improving tolerance of barley to this fungal pathogen.

ITS fungal barcoding primers versus 18S AMF-specific primers reveal similar AMF-based diversity patterns in roots and soils of three mountain vineyards.

ITS primers commonly used to describe soil fungi are flawed for AMF although it is unknown the extent to which they distort the interpretation of community patterns. Here, we focus on how the use of a specific ITS2 fungal barcoding primer pair biased for AMF changes the interpretation of AMF community patterns from three mountain vineyards compared to a novel AMF-specific approach on the 18S. We found that although discrepancies were present in the taxonomic composition of the two resulting datasets, the estimation of diversity patterns among AMF communities was similar and resulted in both primer systems being able to correctly assess the community-structuring effect of location, compartment (root vs. soil) and environment. Both methodologies made it possible to detect the same alpha-diversity trend among the locations under study but not between root and soil transects. We show that the ITS2 primer system for fungal barcoding provides a good estimate of both AMF community structure and relation to environmental variables. However, this primer system does not fit in with cross-compartment surveys (roots vs. soil) as it can underestimate AMF diversity in soil samples. When specifically focusing on AMF, the 18S primer system resulted in wide coverage and marginal non-target amplification.