Abstract
Low phosphate (Pi) availability limits crop growth and yield in acid soils. Although root-associated acid phosphatases (APases) play an important role in extracellular organic phosphorus (P) utilization, they remain poorly studied in soybean (Glycine max), an important legume crop. In this study, dynamic changes in intracellular (leaf and root) and root-associated APase activities were investigated under both Pi-sufficient and Pi-deficient conditions. Moreover, genome-wide identification of members of the purple acid phosphatase (PAP) family and their expression patterns in response to Pi starvation were analyzed in soybean. The functions of both GmPAP7a and GmPAP7b, whose expression is up regulated by Pi starvation, were subsequently characterized. Phosphate starvation resulted in significant increases in intracellular APase activities in the leaves after 4 days, and in root intracellular and associated APase activities after 1 day, but constant increases were observed only for root intracellular and associated APase activities during day 5–16 of P deficiency in soybean. Moreover, a total of 38 GmPAP members were identified in the soybean genome. The transcripts of 19 GmPAP members in the leaves and 17 in the roots were upregulated at 16 days of P deficiency despite the lack of a response for any GmPAP members to Pi starvation at 2 days. Pi starvation upregulated GmPAP7a and GmPAP7b, and they were subsequently selected for further analysis. Both GmPAP7a and GmPAP7b exhibited relatively high activities against adenosine triphosphate (ATP) in vitro. Furthermore, overexpressing GmPAP7a and GmPAP7b in soybean hairy roots significantly increased root-associated APase activities and thus facilitated extracellular ATP utilization. Taken together, these results suggest that GmPAP7a and GmPAP7b might contribute to root-associated APase activities, thus having a function in extracellular ATP utilization in soybean.
Highlights
Phosphorus (P), an important macronutrient, is involved in many biochemical and metabolic processes in plants, such as photosynthesis, nucleotide synthesis, membrane remodeling, and protein modification (Liang et al, 2010; Zhang et al, 2014; Ham et al, 2018)
Overexpressing GmPAP7a and GmPAP7b in soybean hairy roots significantly increased root-associated acid phosphatase (APase) activities and facilitated extracellular adenosine triphosphate (ATP) utilization. These results suggest that GmPAP7a and GmPAP7b might contribute to root-associated APase activities, having a function in extracellular ATP utilization in soybean
In this study, enhanced soybean root growth was observed in soybean in response to Pi starvation, as reflected by increased soybean root fresh weight after 10 days of Pi starvation (Figure 1), strongly suggesting that significant changes in the soybean root system occur under P-deficient conditions
Summary
Phosphorus (P), an important macronutrient, is involved in many biochemical and metabolic processes in plants, such as photosynthesis, nucleotide synthesis, membrane remodeling, and protein modification (Liang et al, 2010; Zhang et al, 2014; Ham et al, 2018). A large proportion of P exists in immobile forms (i.e., organic P esters and inorganic complexes) and is unavailable for plant utilization in most soils, especially in acid soils (Chiou and Lin, 2011; Tian et al, 2012b; Plaxton and Lambers, 2015). It has been well documented that plants have evolved complex adaptation strategies to increase Pi foraging and recycling, such as altering root morphology and architecture, increasing organic acid and PAP exudation, and enhancing root–microbe interactions (Chiou and Lin, 2011; Liang et al, 2014; Ham et al, 2018; Jung et al, 2018)
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