Transcriptome Analysis Unravels Diverse Response Mechanisms of Nodules to Phytic Acid Supply in Vicia faba

Faba bean ( Vicia faba L.) is an essential crop that contributes enormously to nitrogen (N) input due to its ability to fix atmospheric nitrogen via symbiotic N fixation (SNF). During this process, the symbionts undergo cascades of gene expression perturbations and reprogramming in the organogenesis of nodules under nutritional stresses. Inorganic phosphorus (Pi) has been the ultimate source for nodulation, to the neglect of organic P (Po) in many SNF studies. To elucidate the role of Po in SNF, we used de novo RNA-seq tools and the results identified a total of 2,263 differentially expressed genes (DEGs) in nodules when Vicia faba plants were exposed to different P sources, viz., low Pi, high Pi, and Po when inoculated with Rhizobium leguminosarum bv. viciae 3841 in hydrponics experiment. The results consistently reveal that Po-induced nodules comparisons altered 1,144 and 811 DEGs, respectively, relative to the Pi-induced nodules comparison (308 DEGs), highlighting higher DEGs triggered by phytic acid supply. The results further reveal differential nodulation, transport and carbon metabolism mechanisms employed by the different P sources during N-fixation. The expression of these genes in Vicia faba will provide more insights into the functional characterization of these DEGs for breeding purposes, and also contribute enomously towards the ongoing genome annotation project and database of Vicia faba plants.