Growth and nodulation of symbiotic Medicago truncatula at different levels of phosphorus availability

Abstract

Medicago truncatula is an important model plant for characterization of P deficiency on leguminous plants at the physiological and molecular levels. Growth optimization of this plant with regard to P supply is the first essential step for elucidation of the role of P in regulation of nodulation. Hence, a study was carried out to address the growth pattern of M. truncatula hydroponically grown at different gradual increases in P levels. The findings revealed that M. truncatula had a narrow P regime, with an optimum P level (12 μM P) which is relatively close to the concentration that induces P toxicity. The accumulated P concentration (2.7 mg g–1 dry matter), which is normal for other crops and legumes, adversely affected the growth of M. truncatula plants. Under P deficiency, M. truncatula showed a higher symbiotic efficiency with Sinorhizobium meliloti 2011 in comparison with S. meliloti 102F51, partially as a result of higher electron allocation to N2 versus H+. The total composition of free amino acids in the phloem was significantly affected by P deprivation. This pattern was found to be almost exclusively the result of the increase in the asparagine level, suggesting that asparagine might be the shoot-derived signal that translocates to the nodules and exerts the down-regulation of nitrogenase activity. Additionally, P deprivation was found to have a strong influence on the contents of the nodule carbon metabolites. While levels of sucrose and succinate tended to decrease, a higher accumulation of malate was observed. These findings have provided evidence that N2 fixation of M. truncatula is mediated through an N feedback mechanism which is closely related to nodule carbon metabolism.

Adaptation of the symbiotic Mesorhizobium –chickpea relationship to phosphate deficiency relies on reprogramming of whole-plant metabolism

“…S3, S4, and S5 and Datasets S2-S4). These data support the premise that legume nodules subjected to low Pi are not sucrose-limited (13,28). Instead of the initial cleaving of sucrose with the aid of ATPdependent AI, McCP-31-induced nodules subjected to low Pi significantly activated the energy-saving SS/UDP-GPP pathway that remained unaffected in MmSWRI9-induced nodules (Fig.…”

“…S3 and Dataset S2). Several studies have reported that down-regulation of SNF capacity is associated with the accumulation of asparagine in nodules of Pi-stressed plants (28,39). These reports further strengthen the premise that asparagine accumulation plays a role in N feedback regulation of SNF capacity in MmSWRI9-inoculated plants.…”

Validating Genome-Wide Association Candidates Controlling Quantitative Variation in Nodulation

“…PHO2-like is annotated as encoding an E2 ubiquitin conjugating enzyme, and its Arabidopsis (Arabidopsis thaliana) ortholog (35% amino acid identity, E value = 4e-104) is involved in phosphorous accumulation (Park et al, 2014). Not only can phosphorous availability affect nodulation and N 2 fixation (Graham and Rosas, 1979;Jakobsen, 1985;Graham, 1992;Sulieman, 2013) but in Arabidopsis, AtPHO2 ortholog interacts directly with the E3 product of Nitrogen Limitation Adaption, which mediates plant responses to N limitation (Park et al, 2014). Moreover, E2 ubiquitin conjugate enzymes are presumed to interact with multiple E3 partners that could lead to the proteolytic degradation of a larger range of uncharacterized substrates (Smalle and Vierstra, 2004).…”

Nodules from Fynbos legume Virgilia divaricata have high functional plasticity under variable P supply levels

“…Most studies on the effect of P limitation on N 2 -fixation have largely been confined to model legumes such as Lupinus albus (Schulze et al, 2006, Thuynsma et al, 2013 and Medicago truncatula (Tang et al, 2001, Sulieman et al, 2013. Despite the high legume diversity found on the P-poor soils of the CFR (Goldblatt and Manning 2002), little is known about the functional mechanisms which affect N nutrition within the nodules of indigenous legumes.…”