Eliminating the purple acid phosphatase AtPAP26 in Arabidopsis thaliana delays leaf senescence and impairs phosphorus remobilization

Limitation of crop productivity by suboptimal phosphorus (P) nutrition is a widespread concern. Enhanced crop P-use efficiency could be achieved by improving P remobilization from senescing leaves to developing tissues and seeds. Transcriptomic studies indicate that hundreds of Arabidopsis thaliana genes are up-regulated during leaf senescence, including that encoding the purple acid phosphatase (PAP) AtPAP26 (At5g34850). In this study, biochemical and functional genomic tools were integrated to test the hypothesis that AtPAP26 participates in P remobilization during leaf senescence. An eightfold increase in acid phosphatase activity of senescing leaves was correlated with the accumulation of AtPAP26 transcripts and immunoreactive AtPAP26 polypeptides. Senescing leaves of an atpap26 T-DNA insertion mutant displayed a >90% decrease in acid phosphatase activity, markedly impaired P remobilization efficiency and delayed senescence. This was paralleled by reduced seed total P concentrations and germination rates. These results demonstrate that AtPAP26 loss of function causes dramatic effects that cannot be compensated for by any other PAP isozyme, even though Arabidopsis contains 29 different PAP genes. Our current and earlier studies establish that AtPAP26 not only helps to scavenge P from organic P sources when Arabidopsis is cultivated in inorganic orthophosphate (Pi)-deficient soils, but also has an important P remobilization function during leaf senescence.