Endophytic fungus regulates root secretion of IAA and ABA to enhance rice nitrogen accumulation by promoting soil nitrogen fixation

Endophytic fungi can regulate the host rhizosphere microbial community and promote nitrogen nutrient uptake by the host. Our previous research found that the endophytic fungus Phomopsis liquidambaris B3 can optimize the microbial community structure of nitrogen transformation in rice rhizosphere soil, but its mechanism of action is still unclear. Plant hormones play a crucial role in the assembly of plant microbiota, therefore we hypothesize that endophytic fungus B3 promotes nitrogen uptake in rice by influencing phytohormone secretion to reshape the rhizosphere microbiota. In this study, we used liquid chromatography-mass spectrometry to demonstrate that the colonization of endophytic fungus B3 significantly increased the content of auxin and abscisic acid in rice root exudates. The experiment of exogenous hormone addition further showed that auxin and abscisic acid increased the content of ammonium nitrogen in soil, promoted the growth and nitrogen absorption of rice, and significantly upregulated the gene abundance of nifH in soil. In addition, high-throughput sequencing results showed that auxin and abscisic acid significantly altered the structure of the rhizosphere diazotrophs community, particularly increasing the abundance of the Burkholderia sp. strain. In vitro experiments have verified the enrichment effect of phytohormones on Burkholderia sp. and the ability of the strain to promote rice growth. These findings contribute to revealing the ecological functions of plant hormones in the rhizosphere and gaining a deeper understanding of the mechanisms behind the beneficial effects of endophytic fungi on nitrogen utilization in rice.