Comparative metabolomics of root nodules infected with Frankia sp. strains and uninfected roots from Alnus glutinosa and Casuarina cunninghamiana reflects physiological integration
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- Brooks, J.M. & Benson, D.R. Symbiosis (2016) 70: 87. doi:10.1007/s13199-016-0379-x
Nitrogen-fixing root nodules on actinorhizal plants have varying internal architectures, implying diversity in how Frankia sp. integrates into plant physiologies. To understand this integration we compared the metabolomes of Alnus glutinosa and Casuarina cunninghamiana root nodules with roots from uninfected plants. High throughput gas chromatography–mass spectrometry (GC-MS) was done on extracts of nodules and roots from uninfected seedlings. Over 118 metabolites in C. cunninghamiana roots and nodules and over 163 in A. glutinosa roots and nodules were identified; between one-third to one-half of the metabolites significantly increased or decreased between roots and nodules. Amino acid patterns varied between the plants with only glutamate and alanine, which may be conducive to the induction of nitrogenase, and citrulline, elevated in nodules of both. Sugar levels were similar between species excepting a striking increase of maltose and cellobiose in C. cunninghamiana nodules indicating starch mobilization and cell wall modification. Stress related compounds increased in both systems. Phenylacetic acid was elevated in A. glutinosa nodules. High ethanolamine content was found in C. cunninghamiana nodules suggesting lipid degradation. We conclude that C. cunninghamiana responds more robustly to the presence of the endophyte than A. glutinosa with metabolite patterns consistent with different strategies used for compartmentalizing the symbiont from uninfected tissues.