title: Subcellular localization and vacuolar targeting of sorbitol dehydrogenase in apple seed.
abstract: Sorbitol is the primary photosynthate and translocated carbohydrate in fruit trees of the Rosaceae family. NAD(+)-dependent sorbitol dehydrogenase (NAD-SDH, EC 1.1.1.14), which mainly catalyzes the oxidation of sorbitol to fructose, plays a key role in regulating sink strength in apple. In this study, we found that apple NAD-SDH was ubiquitously distributed in epidermis, parenchyma, and vascular bundle in developing cotyledon. NAD-SDH was localized in the cytosol, the membranes of endoplasmic reticulum and vesicles, and the vacuolar lumen in the cotyledon at the middle stage of seed development. In contrast, NAD-SDH was mainly distributed in the protein storage vacuoles in cotyledon at the late stage of seed development. Sequence analysis revealed there is a putative signal peptide (SP), also being predicated to be a transmembrane domain, in the middle of proteins of apple NAD-SDH isoforms. To investigate whether the putative internal SP functions in the vacuolar targeting of NAD-SDH, we analyzed the localization of the SP-deletion mutants of MdSDH5 and MdSDH6 (two NAD-SDH isoforms in apple) by the transient expression system in Arabidopsis protoplasts. MdSDH5 and MdSDH6 were not localized in the vacuoles after their SPs were deleted, suggesting the internal SP functions in the vacuolar targeting of apple NAD-SDH.
authors.affiliation: State Key Laboratory of Crop Biology, College of Life Sciences, Shandong Agricultural University, Taian 271018, China. xlwang@sdau.edu.cn
authors.forename: Xiu-Ling
authors.initials: XL
authors.lastname: Wang
authors.forename: Zi-Ying
authors.initials: ZY
authors.lastname: Hu
authors.forename: Chun-Xiang
authors.initials: CX
authors.lastname: You
authors.forename: Xiu-Zhen
authors.initials: XZ
authors.lastname: Kong
authors.forename: Xiao-Pu
authors.initials: XP
authors.lastname: Shi
mesh_terms: D000595:Amino Acid Sequence; D018548:Cotyledon / Q000201:enzymology / Q000235:genetics / Q000648:ultrastructure; D007150:Immunohistochemistry; D007064:L-Iditol 2-Dehydrogenase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D027845:Malus / Q000201:enzymology* / Q000235:genetics / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D008969:Molecular Sequence Data; D009243:NAD / Q000378:metabolism; D018515:Plant Leaves / Q000201:enzymology / Q000235:genetics / Q000648:ultrastructure; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D021382:Protein Sorting Signals; D021381:Protein Transport; D011993:Recombinant Fusion Proteins; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012639:Seeds / Q000201:enzymology* / Q000235:genetics / Q000648:ultrastructure; D016415:Sequence Alignment; D017384:Sequence Deletion; D013012:Sorbitol / Q000378:metabolism; D014617:Vacuoles / Q000201:enzymology*
chemical_list: D010940:Plant Proteins; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins; D009243:NAD; D013012:Sorbitol; D007064:L-Iditol 2-Dehydrogenase
keywords: Apple cotyledon; Internal signal peptide; Sorbitol dehydrogenase; Subcellular localization; Vacuolar targeting