Elucidating the evolutionary history and expression patterns of nucleoside phosphorylase paralogs (vegetative storage proteins) in Populus and the plant kingdom

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.

Drought response transcriptomes are altered in poplar with reduced tonoplast sucrose transporter expression

“…S4 ). In Populus , BSP/VSP proteins accrue as storage reserves in response to stress and to seasonal changes in temperature and light 34 . However, BSP/VSP is also an important target of the wound signal JA in Populus and other species 35 .…”

RNA-SEQ Reveals Transcriptional Level Changes of Poplar Roots in Different Forms of Nitrogen Treatments

“…Poplar BSP genes, which belong to the nucleoside phosphorylases gene family, are expressed before the metabolic nucleotide salvaging, and play an important role in ecophysiological adaptation for inter- and intra-seasonal N storage and cycling (Pettengill et al, 2013 ). In this study, we obtained a transcription read of bsp-like gene (Comments as PLP; Figure 4 ), which might be a kind of storage protein of a poplar, specifically induced by .…”

Seasonal nitrogen remobilization and the role of auxin transport in poplar trees

“…Seasonal N cycling in the deciduous temperate tree poplar ( Populus ) involves the accumulation of 32 kDa bark storage proteins (BSPs) in protein storage vacuoles of bark phloem parenchyma and xylem ray cells during autumn and the disappearance of these proteins when shoot growth commences in the spring. Poplar BSPs are encoded by three genes ( BSPA , BSPB , and BSPC ) that belong to a family of nucleoside phosphorylase-like proteins of a larger 13 member gene family ( Pettengill et al , 2013 ). BSP expression and protein accumulation are regulated by environmental factors including short-day (SD) photoperiods, N availability, and low temperature ( Coleman et al, 1991 , 1992 , 1994 ; Zhu and Coleman, 2001 a , b ; Wildhagen et al , 2010 ; Pettengill et al , 2013 ).…”