Department of Biology, Queen's University, Kingston, Ontario K7L3N6, Canada.
Plant Cell Environ. 2010 Nov;33(11):1789-803. doi: 10.1111/j.1365-3040.2010.02184.x.
Plant purple acid phosphatases (PAPs) belong to a large multigene family whose specific functions in Pi metabolism are poorly understood. Two PAP isozymes secreted by Pi-deficient (-Pi) Arabidopsis thaliana were purified from culture filtrates of -Pi suspension cells. They correspond to an AtPAP12 (At2g27190) homodimer and AtPAP26 (At5g34850) monomer composed of glycosylated 60 and 55 kDa subunit(s), respectively. Each PAP exhibited broad pH activity profiles centred at pH 5.6, and overlapping substrate specificities. Concanavalin-A chromatography resolved a pair of secreted AtPAP26 glycoforms. AtPAP26 is dual targeted during Pi stress because it is also the principal intracellular (vacuolar) PAP up-regulated by -Pi Arabidopsis. Differential glycosylation appears to influence the subcellular targeting and substrate selectivity of AtPAP26. The significant increase in secreted acid phosphatase activity of -Pi seedlings was correlated with the appearance of immunoreactive AtPAP12 and AtPAP26 polypeptides. Analysis of atpap12 and atpap26 T-DNA mutants verified that AtPAP12 and AtPAP26 account for most of the secreted acid phosphatase activity of -Pi wild-type seedlings. Semi-quantitative RT-PCR confirmed that transcriptional controls exert little influence on the up-regulation of AtPAP26 during Pi stress, whereas AtPAP12 transcripts correlate well with relative levels of secreted AtPAP12 polypeptides. We hypothesize that AtPAP12 and AtPAP26 facilitate Pi scavenging from soil-localized organophosphates during nutritional Pi deprivation.
植物紫色酸性磷酸酶（PAPs）属于一个庞大的多基因家族，其在磷代谢中的特定功能知之甚少。从缺磷（-Pi）拟南芥悬浮细胞的培养滤液中纯化出两种由 Pi 缺乏诱导的 PAP 同工酶。它们分别对应于 AtPAP12（At2g27190）同源二聚体和 AtPAP26（At5g34850）单体，由糖基化的 60 和 55 kDa 亚基组成。每种 PAP 均表现出以 pH5.6 为中心的广泛 pH 活性谱，并且具有重叠的底物特异性。刀豆凝集素层析分离出一对分泌的 AtPAP26 糖型。AtPAP26 在 Pi 胁迫期间是双重靶向的，因为它也是由 -Pi 诱导的主要细胞内（液泡）PAP。差异糖基化似乎会影响 AtPAP26 的亚细胞靶向和底物选择性。-Pi 幼苗分泌的酸性磷酸酶活性的显著增加与免疫反应性 AtPAP12 和 AtPAP26 多肽的出现相关。atpap12 和 atpap26 T-DNA 突变体的分析证实，AtPAP12 和 AtPAP26 占 -Pi 野生型幼苗分泌的酸性磷酸酶活性的大部分。半定量 RT-PCR 证实，转录控制对 Pi 胁迫下 AtPAP26 的上调几乎没有影响，而 AtPAP12 转录物与分泌的 AtPAP12 多肽的相对水平密切相关。我们假设 AtPAP12 和 AtPAP26 在营养 Pi 缺乏时促进从土壤定位的有机磷中摄取 Pi。
