Global Changes in the Transcript and Metabolic Profiles during Symbiotic Nitrogen Fixation in Phosphorus-Stressed Common Bean Plants    

Abstract

Phosphorus (P) deficiency is widespread in regions where the common bean (Phaseolus vulgaris), the most important legume for human consumption, is produced, and it is perhaps the factor that most limits nitrogen fixation. Global gene expression and metabolome approaches were used to investigate the responses of nodules from common bean plants inoculated with Rhizobium tropici CIAT899 grown under P-deficient and P-sufficient conditions. P-deficient inoculated plants showed drastic reduction in nodulation and nitrogenase activity as determined by acetylene reduction assay. Nodule transcript profiling was performed through hybridization of nylon filter arrays spotted with cDNAs, approximately 4,000 unigene set, from the nodule and P-deficient root library. A total of 459 genes, representing different biological processes according to updated annotation using the UniProt Knowledgebase database, showed significant differential expression in response to P: 59% of these were induced in P-deficient nodules. The expression platform for transcription factor genes based in quantitative reverse transcriptase-polymerase chain reaction revealed that 37 transcription factor genes were differentially expressed in P-deficient nodules and only one gene was repressed. Data from nontargeted metabolic profiles indicated that amino acids and other nitrogen metabolites were decreased, while organic and polyhydroxy acids were accumulated, in P-deficient nodules. Bioinformatics analyses using MapMan and PathExpress software tools, customized to common bean, were utilized for the analysis of global changes in gene expression that affected overall metabolism. Glycolysis and glycerolipid metabolism, and starch and Suc metabolism, were identified among the pathways significantly induced or repressed in P-deficient nodules, respectively.A key to the success of the legume family, which comprises approximately 700 genera with more than 18,000 species (Doyle and Luckow, 2003), was the evolution of mutualistic symbioses with nitrogen (N)-fixing bacteria of the family Rhizobiaceae to directly capture atmospheric dinitrogen (N 2 ) to support plant growth. Symbiotic nitrogen fixation (SNF) takes place in specialized rhizobia-induced legume root nodules and involves a tight association between the two symbionts. SNF and legume crop production might be affected by disease and insect pressures but also by edaphic constraints that include climatic conditions, nutrient deficiency, soil acidity, and metal toxicity.Phosphorus (P) is an essential macronutrient for plant growth and development, with P concentration ranging from 0.05% to 0.5% plant dry weight. P is taken by the plants as phosphate (P i ), but P i is unevenly distributed and relatively immobile in soils. As

Root Exudates and Their Molecular Interactions with Rhizospheric Microbes

“…Moreover, legume plants exhibit some of the biologically signifi cant property, viz., fi xation of atmospheric nitrogen through symbiotic association with rhizobacteria. Some of the commonly explored plants for root exudates and other metabolites include Medicago sativa , Trifolium repens , Pisum sativum , Lotus japonicus , Medicago truncatula , Phaseolus vulgaris , and Glycine max (Desbrosses et al 2005 ;Farag et al 2009 ;Hernandez et al 2009 ;Rispail et al 2010 ;Sugiyama and Yazaki 2012 ). Most of the characteristic properties and primary metabolic activities involved in symbiotic nitrogen fi xation have been discovered through various classical methods involving studies on plant biochemistry, genetics, and molecular biology.…”

The High-Affinity Phosphate Transporter GmPT5 Regulates Phosphate Transport to Nodules and Nodulation in Soybean

“…But there is no report on legume Pi transporters involved in maintaining Pi homeostasis in nodules. Recently, most studies on soybean nodules have analyzed transcriptome and protein profiles of low-P-stressed nodules or bacteroids within nodules, identifying some nodule-specific genes and proteins involved in carbon and N metabolism or genes related to transcription and signaling (Hernández et al, 2009;Chen et al, 2011), but no nodule-specific Pi transporter has been found in soybean. As a strong Pi sink, especially under P-limiting conditions, the import of Pi from other organs has been speculated to be important to nodule P nutrition.…”

“…Developing legume varieties with effective N 2 fixation under P-limited conditions will be important to reduce N and P fertilization and enhance agricultural sustainability. P deficiency severely inhibits both nodule growth and N 2 -fixing capacity (Chaudhary et al, 2008;Hernández et al, 2009). In order to maintain growth and high N 2 fixation rate, P levels need to be maintained in the nodules.…”

EFFECT OF RESIDUAL ROCK PHOSPHATE AND BIOFERTILIZERS (RHIZOBIUM AND BIOPHOSPHATE) AND THEIR COMBINATIONS ON THE PRODUCTIVITY OF Stylosanthes guianensis CIAT 184

“…Sensitivity of symbiotic nitrogen fixation to phosphorus deficiency could have affected the CP production; if bio-phosphate microbes were rendered dormant due to the above mentioned conditions, P-deficiency would drastically cause a reduction in nodulation (Hernandez et al, 2009) and nitrogenase activity.…”

“…The success of legumes is found in their ability to have a mutualistic symbioses with nitrogen (N)-fixing bacteria to directly capture atmospheric dinitrogen (N 2 ) to support plant growth (Hernandez et al, 2009). Nitrogen is commonly the most limiting plant nutrient in arable farming in the tropics and also the most expensive element as a mineral fertilizer, biological nitrogen fixation (BNF) therefore, holds great promise for smallholder farmers (Tripathi and Psychas, 1992).…”