Plant growth-promoting effects and possible mechanisms of a plant endophytic fungus Aureobasidium sp. JRF1.

Endophytic fungi can establish symbiosis with host plant and promote plant growth in a sustainable way. In this study, a previously-isolated plant growth-promoting endophytic fungus JRF1 was deeply studied. JRF1 could colonize Arabidopsis and tomato seedlings and promote their growth. Through sequencing the internal transcribed spacer (ITS) region and 18S rRNA gene, JRF1 was identified as an Aureobasidium sp. strain. Transcriptome analysis indicated that JRF1 treatment up-regulated a majority of genes related to calcium signal and genes annotated as peroxidase and glutathione S- transferase. In addition, treatment with JRF1 activated the Aux/IAA (auxin/indole acetic acid) and cytokinin signaling, while down-regulated genes involved in JA/ETH (jasmonic acid/ethylene) pathways. Split co-culture assay not only demonstrated that JRF1 significantly promoted the Arabidopsis growth by direct contacting the seedlings, but also suggested JRF1 could exhibit positive effects in a non-contact manner. Subsequently, metabolome analysis revealed that JRF1 produced many soluble metabolites which might be responsible for plant growth-promoting, and the releasing volatile organic compounds (VOCs) of JRF1 was also isolated and detected. Finally, we found that both cell-free supernatant (CFS) of JRF1 and its fermentation solution could outstandingly promote the plant growth, suggesting its possible role as a microbial fertilizer. Our results uncovered the interaction mode between JRF1 and host plant, proposing that the combined action of JRF1 with its metabolites resulted in the enhanced plant growth.