Plant growth-promoting archaea trigger induced systemic resistance in Arabidopsis thaliana against Pectobacterium carotovorum and Pseudomonas syringae.

Archaea have inhabited the earth for a long period of time and are ubiquitously distributed in diverse environments. However, few studies have focused on the interactions of archaea with other organisms, including eukaryotes such as plants, since it is difficult to cultivate sufficient numbers of archaeal cells for analysis. In this study, we investigated the interaction between soil archaea and Arabidopsis thaliana. We demonstrate for the first time that soil archaea promote plant growth and trigger induced systemic resistance (ISR) against the necrotrophic bacterium Pectobacterium carotovorum subsp. carotovorum SCC1 and biotrophic bacterium Pseudomonas syringae pv. tomato DC3000. Ammonia-oxidizing archaeon Nitrosocosmicus oleophilus MY3 cells clearly colonized the root surface of Arabidopsis plants, and increased resistance against both pathogenic species via the salicylic acid-independent signalling pathway. This mechanism of bacterial resistance resembles that underlying soil bacteria- and fungi-mediated ISR signalling. Additionally, volatile emissions from N. oleophilus MY3 were identified as major archaeal determinants that elicit ISR. Our results lay a foundation for archaea-plant interactions as a new field of research.