Micromonospora accelerates the nodulation of Rhizobium in chickpea (Cicer arietinum L) via hormones

Chickpea (Cicer arietinum L) is the third largest legume crop, with characteristics such as drought resistance, barren tolerance, nitrogen fixation and habitat for nitrogen-fixing bacteria, but also a habitat for various symbiotic microorganisms such as Micromonospora. The study of the co-relationship between Micromonospora and Rhizobia in root nodules are of great significance for deeply revealing the mechanism of nodulation and nitrogen fixation. Through culture-free sequencing, it was found that rhizobia and Micromonospora exist in root nodules and were used to laser confocal microscopy observations on three strains of Rhizobium-RFP-labeled and four strains of Micromonospora-GFP-labeled for single inoculation and co-inoculation, the results showed that the colonization of Micromonospora in root nodules was a common phenomenon, and both Rhizobia and Micromonospora could colonize independently in root nodules with consistent infection pathway and Micromonospora accelerated the formation of root nodule primordia. Based on bioinformatics technology, the possible hormones produced by Micromonospora were predicted. The contents of hormones produced by Micromonospora was detected by HRMS, and nodulation genes were analyzed bytranscriptome and qPCR to accelerate Rhizobia-chickpea nodulation. The results showed that Micromonospora increased the expression of auxin-related factor ARF3, isopentenyl transferase IPT, cytokinin receptor. The combined action of two hormones accelerates the formation of root nodule primordia, thereby accelerating the nodulation of Rhizobia-chickpea.