Abstract
Aspartate aminotransferase (AspAT) catalyzes a reversible transamination reaction between glutamate and oxaloacetate to yield aspartate and 2-oxoglutarate, exerting a primary role in amino acid biosynthesis and homeostasis of nitrogen (N) and carbon metabolism within all cellular organisms. While progress in biochemical characterization of AspAT has been made for decades, the molecular and physiological characteristics of different members of the AspAT gene family remain poorly known particularly in forest trees. Here, extensive genome-wide survey of AspAT encoding genes was implemented in black cottonwood (Populus trichocarpa Torr. & A. Gray), a model species of woody plants. Thorough inspection of the phylogenies, gene structures, chromosomal distribution, cis-elements, conserved motifs, and subcellular targeting resulted in the identification of 10 AspAT isogenes (PtAspAT1-10) in the Populus genome. RNA-seq along with quantitative real-time polymerase chain reaction (qRT-PCR) validation revealed that PtAspATs displayed diverse patterns of tissue-specific expression. Spatiotemporal expressions of homologous AspATs in the poplar hybrid clone ‘Nanlin895’ were further evaluated, showing that gene expressions varied depending on source-sink dynamics. The impact on AspAT transcripts upon N starvation and seasonal senescence showed the upregulation of five AspAT in leaves concurrent with drastic downregulation of six or more AspATs in roots. Additionally, marked reductions of many more AspATs transcripts were observed in roots upon N excess. Accordingly, AspAT activities were significantly suppressed upon N starvation by an in-gel assay, prompting the argument that enzyme activity was a more direct indicator of the growth morphology under a N stress regime. Taken together, the expression profiling and enzyme activities upon stress cues provide a theoretical basis for unraveling the physiological significance of specific gene(s) in regulation of N acquisition and remobilization in woody plants.
Highlights
Nitrogen (N) is an essential nutritional element for plants and their interaction with the environment
In silico prediction of their targeting organelles suggested that PtAspATs were localized to the chloroplasts (PtAspAT1, 5, 6, and 9), cytosols (PtAspAT3, 4 and 10), and mitochondria (PtAspAT2 and PtAspAT7)
Aspartate aminotransferase (AspAT) is an important aminotransferase enzyme and exerts specific functions other than merely catalyzing the formation of Asp, which is regarded as an essential intermediate for protein synthesis [60]
Summary
Nitrogen (N) is an essential nutritional element for plants and their interaction with the environment. Asp serves as a substrate for asparagine (Asn) synthesis in cytosols and is a precursor involved in the biosynthesis of four key essential amino acids; methionine, lysine, threonine, and isoleucine in plastids [2,3]. The former two have been well explored to function as the most limiting amino acids in grains of cereals and legume crops, which may be utilized as major nutrient resources for human and livestock feed [4,5]. Asp has been reported to play primary roles as N donors and carriers, supplying amide precursors for the synthesis of N transport compounds, when the recycling of C skeletons are confined in roots under dark conditions, suggesting its association with
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
