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

Abstract

Legume biological nitrogen (N) fixation is the most important N source in agroecosystems, but it is also a process requiring a considerable amount of phosphorus (P). Therefore, developing legume varieties with effective N 2 fixation under P-limited conditions could have profound significance for improving agricultural sustainability. We show here that inoculation with effective rhizobial strains enhanced soybean (Glycine max) N 2 fixation and P nutrition in the field as well as in hydroponics. Furthermore, we identified and characterized a nodule high-affinity phosphate (Pi) transporter gene, GmPT5, whose expression was elevated in response to low P. Yeast heterologous expression verified that GmPT5 was indeed a high-affinity Pi transporter. Localization of GmPT5 expression based on b-glucuronidase staining in soybean composite plants with transgenic roots and nodules showed that GmPT5 expression occurred principally in the junction area between roots and young nodules and in the nodule vascular bundles for juvenile and mature nodules, implying that GmPT5 might function in transporting Pi from the root vascular system into nodules. Overexpression or knockdown of GmPT5 in transgenic composite soybean plants altered nodulation and plant growth performance, which was partially dependent on P supply. Through both in situ and in vitro 33 P uptake assays using transgenic soybean roots and nodules, we demonstrated that GmPT5 mainly functions in transporting Pi from roots to nodules, especially under P-limited conditions. We conclude that the high-affinity Pi transporter, GmPT5, controls Pi entry from roots to nodules, is critical for maintaining Pi homeostasis in nodules, and subsequently regulates soybean nodulation and growth performance.

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

“…Because Pi deficiency-induced inhibition of SNF is caused by dramatic reductions in the cytosolic Pi pool in nodules, maintenance of an appropriate nodular Pi level represents a critical adaptive strategy for nodules to diminish the adverse effects of Pi deficiency on SNF capacity (6,8,20). In this study, there was an apparent difference between the two symbiotic systems regarding the maintenance of Pi homeostasis in their organs, particularly nodules and roots, for acclimation to low Pi stress.…”

“…2). Pi concentrations need to be conserved in the roots to facilitate the acquisition of external Pi sources and upgrade the level of Pi in nodules during Pi starvation conditions (8,21), as observed with the McCP-31-inoculated plants under Pi-deficient conditions (Fig. 2).…”

“…The development of Pi-efficient crop plants that can grow and yield better under low Pi supply would have a significant beneficial impact on agricultural sustainability (8).…”

GmEXPB2, a Cell Wall β-Expansin Gene, Affects Soybean Nodulation through Modifying Root Architecture and Promoting Nodule Formation and Development

“…Soybean transgenic hairy roots and nodules harboring ProGmEXPB2::GUS or CaMV35S::GUS were generated using the hypocotyl injection method as described previously (Qin et al, 2012). Roots and nodules were harvested at 7, 14, 21, 30, and 40 dai with BXYD3.…”

“…It has been found that phosphate (Pi) starvation-induced P transporters in rhizobia are required for symbiotic N 2 fixation (Bardin et al, 1996). In soybean, maintaining Pi homeostasis in nodules through enhanced P transporters is very important for N 2 fixation efficiency (Qin et al, 2012). Moreover, several genes such as phosphoenol pyruvate phosphatase in common bean (Bargaz, et al, 2012) and purple acid phosphatase in soybean (Li et al, 2012) are highly upregulated in nodules at low P level, implying that these genes might be involved in the adaptation of symbiosis to Pi starvation.…”