Biotic and abiotic stress distinctly drive the phyllosphere microbial community structure

Abstract

While the physiological and transcriptional response of the host to biotic and abiotic stresses have been intensely studied, little is known about the resilience of associated microbiomes and their contribution towards tolerance to these stresses. We evaluated the impact of one such abiotic stress, elevated tropospheric ozone (O3), under open-top chamber field conditions on host susceptibility and phyllosphere microbiome associated with pepper cultivars resistant and susceptible to Xanthomonas. Pathogen challenge resulted in distinct microbial community structures in both cultivars under an ambient environment. Elevated O3 alone affected microbial community structure associated with resistant cultivar but not the susceptible cultivar, indicating the role of host genotypic background in response to abiotic stress. Elevated O3 did not influence overall host susceptibility but did increase disease severity on the resistant cultivar, indicating a possible compromise in the resistance. Interestingly, combined stress resulted in a shift in microbial composition and structure like that observed with pathogen challenge alone. It indicates the possible prioritization of community response towards the most significant stress and pathogen being most influential regardless of the cultivar. Despite community composition differences, overall functional redundancy was observed in the phyllosphere community. To gain insights into community-level interactions, network topology assessment indicated a stable network with enhanced taxon connectedness upon pathogen challenge. However, an observation of destabilized random network with a shift in hub taxa in the presence of combined stress warrants future studies on the consequences of such unstable microbial communities on host response to pathogens in the face of climate change.