Characterization of Purple Acid Phosphatase Family and Functional Analysis ofGmPAP7a/7bInvolved in Extracellular ATP Utilization in Soybean

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 thepurple acid phosphatase(PAP) family and their expression patterns in response to Pi starvation were analyzed in soybean. The functions of bothGmPAP7aandGmPAP7b, 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 38GmPAPmembers were identified in the soybean genome. The transcripts of 19GmPAPmembers in the leaves and 17 in the roots were upregulated at 16 days of P deficiency despite the lack of a response for anyGmPAPmembers to Pi starvation at 2 days. Pi starvation upregulatedGmPAP7aandGmPAP7b, and they were subsequently selected for further analysis. Both GmPAP7a and GmPAP7b exhibited relatively high activities against adenosine triphosphate (ATP)in vitro. Furthermore, overexpressingGmPAP7aandGmPAP7bin 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.