Host species and microplastics differentiate the crop root endophytic antibiotic resistome

The increasing One-Health concept calls for a more in-depth understanding of the dissemination of antibiotic resistance in plant microbiomes. While there is considerable published evidence that microplastics can promote the spread of antibiotic resistance genes (ARGs) in the environment, whether and how microplastics impact the plant endophytic resistome are largely unknown. Here we examined the ARGs along the soil-root continuum of maize and wheat under the pressure of microplastics. Amendment with heavy metals was also included as they can apply the selective pressure for ARG spread as well. The crop species and genotypes had significant effects on the root endophytic ARG abundance and diversity. The greatest ARG abundance was observed in the maize ZD958 endophytes (0.215 copies per 16S rRNA gene), followed by the maize XY335 (0.092 copies per 16S rRNA gene). For each crop genotype, amendment with microplastics and heavy metals significantly increased the ARG abundances and changed their profiles in root endophytes. The endophytic ARG variances were closely associated with the endophytic microbiome, the rhizosphere bacterial communities and resistome. Additionally, the level of endophytic ARGs was positively relevant to the abundance of mobile genetic elements (MGEs). These findings suggested that the root endophytic resistome was primarily affected by the crop species, and microplastics might show enhancement effects on the endophytic resistome via changing the root-associated microbiome and facilitating the MGE mediation. Overall, this study, for the first time, highlights the root endophytic ARG emergence and dissemination induced by microplastics.