Transcriptome of Frankia in nitrogen-fixing root-nodule symbiosis with Datisca glomerata. Frankia

A transcriptome of Cluster II Frankia in nitrogen-fixing root-nodule symbiosis with the host plant, Datisca glomerata, was obtained by Illumina sequencing and mapping to the corresponding published genome (NCBI Bioproject PRJNA46257). Major metabolic pathways detected in Cluster II Frankia in symbiosis with Datisca glomerata were comparable to those described as up-regulated in the Frankia alni-Alnus glutinosa symbiosis (N Alloisio et al, MPMI 23(5):593-607, 2010): nitrogenase biosynthesis, tricarboxylic acid cycle, respiratory-chain related functions, oxidation protection, and terpenoid biosynthesis. These functions are consistent with the primary activities of Frankia in root nodules, e.g. to carry out the energetically-demanding fixation of atmospheric dinitrogen to ammonium, and to maintain internal reducing conditions. Expression of genes coding for amino-acid biosynthetic pathways, including arginine as reported previously (AM Berry et al. Funct Plant Biol 38, 645–652, 2011) was detected. A striking difference from other Frankia strains, revealed in the transcriptome of the Cluster II Frankia in symbiosis, was the expression of homologs of rhizobial nodulation genes, nodA, nodB and nodC. Overall design: Total RNA was extracted from indeterminate root nodules of Datisca glomerata, in early nitrogen-fixation stage, to catalog the gene-expression patterns of Frankia, the microsymbiont, integrated over different stages of symbiotic development.