Abstract
BackgroundNucleoside phosphorylases (NPs) have been extensively investigated in human and bacterial systems for their role in metabolic nucleotide salvaging and links to oncogenesis. In plants, NP-like proteins have not been comprehensively studied, likely because there is no evidence of a metabolic function in nucleoside salvage. However, in the forest trees genus Populus a family of NP-like proteins function as an important ecophysiological adaptation for inter- and intra-seasonal nitrogen storage and cycling.ResultsWe conducted phylogenetic analyses to determine the distribution and evolution of NP-like proteins in plants. These analyses revealed two major clusters of NP-like proteins in plants. Group I proteins were encoded by genes across a wide range of plant taxa while proteins encoded by Group II genes were dominated by species belonging to the order Malpighiales and included the Populus Bark Storage Protein (BSP) and WIN4-like proteins. Additionally, we evaluated the NP-like genes in Populus by examining the transcript abundance of the 13 NP-like genes found in the Populus genome in various tissues of plants exposed to long-day (LD) and short-day (SD) photoperiods. We found that all 13 of the Populus NP-like genes belonging to either Group I or II are expressed in various tissues in both LD and SD conditions. Tests of natural selection and expression evolution analysis of the Populus genes suggests that divergence in gene expression may have occurred recently during the evolution of Populus, which supports the adaptive maintenance models. Lastly, in silico analysis of cis-regulatory elements in the promoters of the 13 NP-like genes in Populus revealed common regulatory elements known to be involved in light regulation, stress/pathogenesis and phytohormone responses.ConclusionIn Populus, the evolution of the NP-like protein and gene family has been shaped by duplication events and natural selection. Expression data suggest that previously uncharacterized NP-like proteins may function in nutrient sensing and/or signaling. These proteins are members of Group I NP-like proteins, which are widely distributed in many plant taxa. We conclude that NP-like proteins may function in plants, although this function is undefined.
Highlights
Nucleoside phosphorylases (NPs) have been extensively investigated in human and bacterial systems for their role in metabolic nucleotide salvaging and links to oncogenesis
PNI 288 clustered within the cluster composed of WIN4 and Bark Storage Protein (BSP) subfamilies, but based on this analysis the protein is distinct from the WIN4 and BSP subfamilies (Figure 1A)
Our investigation into the functional significance and evolutionary history of NP-like proteins and genes within Populus and across the plant kingdom illustrates the importance of both microevolutionary and macroevolutionary forces in shaping patterns of diversity within this protein family
Summary
Nucleoside phosphorylases (NPs) have been extensively investigated in human and bacterial systems for their role in metabolic nucleotide salvaging and links to oncogenesis. NP-like proteins have not been comprehensively studied, likely because there is no evidence of a metabolic function in nucleoside salvage. Nucleotides, nucleotide precursors and derivatives are essential components for life. They compose nucleic acids, act as signaling molecules, intercellular energy transporters, and can be converted to essential enzymatic cofactors. In mammalian and bacterial systems, nucleoside phosphorylases (NPs) salvage nucleosides by cleaving the glycosidic bond of (deoxy-) ribonucleosides in the presence of inorganic phosphate (Pi) to yield (deoxy-) ribose-1-phosphate and a nucleobase [1,3]. The most widely studied NPs are purine nucleoside phosphorylases (PNPs), which are a focus in clinical and cancer research for their role in mutationrelated immunodeficiency diseases, prostate cancer, leukemia and periodontal disease [4,5,6]
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