title: Proteomics of nitrogen remobilization in poplar bark.
abstract: Seasonal nitrogen (N) cycling in temperate deciduous trees involves the accumulation of bark storage proteins (BSPs) in phloem parenchyma and xylem ray cells. BSPs are anabolized using recycled N during autumn leaf senescence and later become a source of N during spring shoot growth as they are catabolized. Little is known about the catabolic processes involved in remobilization and reutilization of N from BSPs in trees. In this study, we used multidimensional protein identification technology (MudPIT) and spectral counting to identify protein changes that occur in the bark during BSP catabolism. A total of 4,178 proteins were identified from bark prior to and during BSP catabolism. The majority (62%) of the proteins were found during BSP catabolism, indicating extensive remodeling of the proteome during renewed shoot growth and N remobilization. Among these proteins were 30 proteases, the relative abundances of which increased during BSP catabolism. These proteases spanned a range of families including members of the papain-like cysteine proteases, serine carboxypeptidases, and aspartyl proteases. These data identify, for the first time, candidate proteases that could potentially provide hydrolase activity required for N remobilization from BSPs and provide the foundation for research to advance our knowledge of poplar N cycling.
authors.affiliation: Department of Plant Sciences and Landscape Architecture, University of Maryland , College Park, Maryland 20742, United States.
authors.forename: Nazrul
authors.initials: N
authors.lastname: Islam
authors.forename: Gen
authors.initials: G
authors.lastname: Li
authors.forename: Wesley M
authors.initials: WM
authors.lastname: Garrett
authors.forename: Rongshuang
authors.initials: R
authors.lastname: Lin
authors.forename: Ganesh
authors.initials: G
authors.lastname: Sriram
authors.forename: Bret
authors.initials: B
authors.lastname: Cooper
authors.forename: Gary D
authors.initials: GD
authors.lastname: Coleman
mesh_terms: D013058:Mass Spectrometry; D009584:Nitrogen / Q000378:metabolism*; D010802:Phylogeny; D024301:Plant Bark / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism*; D032107:Populus / Q000378:metabolism*; D040901:Proteomics
chemical_list: D010940:Plant Proteins; D009584:Nitrogen
keywords: MudPIT; Populus; mass spectrometry; protease; storage