Biochemical characterization of common bean PvPAP26, a ubiquitous purple acid phosphatase that is highly expressed during seedling development

Abstract Phosphatases are important enzymes involved in phosphate acquisition. Seedlings require high amounts of phosphate during early development, as it is a key component of nucleic acids and other essential molecules. However, knowledge about phosphate recycling during seedling development in plants is still limited. In Phaseolus vulgaris (common bean), total phosphatase activity increases during post-germinative development. The major phosphatase, detected by in-gel assays, was purified from embryonic axes. The purified protein was analyzed by MALDI-TOF/TOF mass spectrometry, which enabled identification of the corresponding gene through database searches. This gene was classified as a member of the Purple Acid Phosphatase (PAP) family. Inhibitor studies performed with the purified protein further confirmed its classification as a PAP. The PAP gene family in common bean consists of 26 members. Among the PAP proteins identified in Arabidopsis thaliana , the purified protein showed highest sequence homology with AtPAP26 and was therefore named as PvPAP26. The gene PvPAP26 was expressed in all the tissues analyzed, both in seedlings and mature plants, with the highest expression observed in cotyledons during the phase of intense nutrient mobilization. Gene expression in seedlings was not affected by treatments with methyl jasmonate, phosphate supplementation, or salt stress. In leaves, gene expression was not altered by salt stress, wounding, or dark-induced senescence. These results indicate that PvPAP26 is ubiquitously expressed across all examined tissues, with markedly higher expression in cotyledons shortly after germination. A potential role for this protein in nutrient mobilization during early seedling development is discussed.