GmPAP12 Is Required for Nodule Development and Nitrogen Fixation Under Phosphorus Starvation in Soybean

Abstract

Nodulation process in legume plants is essential for biological nitrogen fixation during which process a large amount of phosphorus (P) is required. Under P deficiency, nodule formation is greatly affected, and induction of purple acid phosphatases (PAPs) is an adaptive strategy for nodules to acquire more P. However, regulation roles of PAPs in nodules remain largely understood. In this study, by transcriptome sequencing technology, five PAP genes were found to be differentially expressed, which led to the greatly increased acid phosphatase (APase) and phytase activities in soybean mature nodules under P starvation conditions; and among the five PAP genes, GmPAP12 had the highest transcript level, and RT-PCR indicated expression of GmPAP12 was gradually increasing during nodule development. GUS activity driven by GmPAP12 promoter was also significantly induced in low phosphorus conditions. Further functional analysis showed that under low phosphorus stress, overexpression of GmPAP12 resulted in higher nodule number, fresh weight, and nitrogenase activity as well as the APase activity than those of control plant nodules, whereas the growth performance and APase activity of nodules on hairy roots were greatly lower when GmPAP12 was suppressed, indicating that GmPAP12 may promote P utilization in soybean nodules under low P stress, which thus played an important role in nodulation and biological nitrogen fixation. Moreover, P1BS elements were found in the promoter of GmPAP12, and yeast one-hybrid experiment further proved the binding of P1BS by transcription factor GmPHR1 in the promoter of GmPAP12. At last, overexpression and suppression of GmPHR1 in nodules indeed caused highly increased and decreased expression of GmPAP12, respectively, indicating that GmPAP12 is regulated by GmPHR1 in soybean nodules. Taken together, these data suggested that GmPAP12 was a novel soybean PAP involved in the P utilization and metabolism in soybean root nodules and played an important role in the growth and development of root nodules and biological nitrogen fixation.

Rhizobial–Host Interactions and Symbiotic Nitrogen Fixation in Legume Crops Toward Agriculture Sustainability

“…The transcriptomic analysis provides another high-throughput tool to relate to a gene function. Using this technique, involvement of the GmPAP12 gene in nodule development was demonstrated (Wang et al, 2020a).…”

Nitrogen and Phosphorus Signaling and Transport During Legume–Rhizobium Symbiosis

“…In addition to root epidermis, cortex, vascular tissues, and root tips, MtPT6 was also expressed in nodules, suggesting that it may play a role in Pi uptake from soil and transporting Pi to nodules from other tissues ( Cao et al, 2020 ). Pi deficiency induces the expression of purple acid phosphatase (PAPs) in root nodules, which leads to an enhanced acquisition and utilization of P in root nodules ( Li et al, 2017 ; Wang et al, 2020e ). Furthermore, under conditions of Pi starvation, GmPHR1 can bind to the promoter sequence and activate the expression of GmPAP12 to maintain the P homeostasis and N fixation ( Wang et al, 2020e ).…”

“…Pi deficiency induces the expression of purple acid phosphatase (PAPs) in root nodules, which leads to an enhanced acquisition and utilization of P in root nodules ( Li et al, 2017 ; Wang et al, 2020e ). Furthermore, under conditions of Pi starvation, GmPHR1 can bind to the promoter sequence and activate the expression of GmPAP12 to maintain the P homeostasis and N fixation ( Wang et al, 2020e ).…”

Genome-Wide Characterization and Evolutionary Analyses of Purple Acid Phosphatase (PAP) Gene Family with Their Expression Profiles in Response to Low Phosphorus Stresses in Moso Bamboo (Phyllostachys edulis)

“…In the long-term evolution of plants, a series of morphological and physiological adaptation mechanisms have evolved to cope with a low phosphorus stress environment. Low phosphorus can induce a series of endogenous hormone secretion, acid phosphatase secretion [12], organic acid metabolism enhancement [13] and the expression of related genes [14], thereby promoting root elongation, organic acid and proton secretion [15]. These low phosphorus responses and adaptation mechanisms activate the phosphorus in the rhizosphere soil for plant utilization, enhance the root system's phosphorus-seeking ability and enhance the plant's phosphorus reuse efficiency [16].…”

“…Purple acid phosphatase (PAP) is a kind of acid phosphatase that widely exists in microorganisms, plants and animals, and is a member of the metallophosphatase family [14]. The structure of PAPs is highly conserved, and the protein contains five conserved domains (the underline indicates seven metal paired amino acid residues), namely DXG/GDXXY/GNH(D/E)/VXXH/GHXH [18].…”