Abstract
Asparagine, a key amino acid for nitrogen storage and transport in plants, is synthesized via the ATP-dependent reaction catalyzed by the enzyme asparagine synthetase (AS; EC 6.3.5.4). In this work, we present the molecular analysis of two full-length cDNAs that encode asparagine synthetase in maritime pine (Pinus pinaster Ait.), PpAS1, and PpAS2. Phylogenetic analyses of the deduced amino acid sequences revealed that both genes are class II AS, suggesting an ancient origin of these genes in plants. A comparative study of PpAS1 and PpAS2 gene expression profiles showed that PpAS1 gene is highly regulated by developmental and environmental factors, while PpAS2 is expressed constitutively. To determine the molecular mechanisms underpinning the differential expression of PpAS1, the promoter region of the gene was isolated and putative binding sites for MYB transcription factors were identified. Gel mobility shift assays showed that a MYB protein from Pinus taeda (PtMYB1) was able to interact with the promoter region of PpAS1. Furthermore, transient expression analyses in pine cells revealed a negative effect of PtMYB1 on PpAS1 expression. The potential role of MYB factors in the transcriptional regulation of PpAS1 in vascular cells is discussed.
Highlights
Asparagine is an important amino acid in plants because it has a high ratio of N/C compared to other amino acids, making it an ideal nitrogen storage and transport compound (Lea et al, 2007)
It was recently reported that the aspartate kinase (AK) and asparagine synthetase (AS) genes are inversely regulated by bZIP transcription factors in Arabidopsis (Ufaz et al, 2011)
IDENTIFICATION AND MOLECULAR CHARACTERIZATION OF TWO ASPARAGINE SYNTHETASE GENES IN MARITIME PINE A Southern blot analysis of the Scots pine (P. sylvestris) asparagine synthetase (AS) carried out by Cañas et al (2006) suggested that there is more than one AS gene in the pine genome
Summary
Asparagine is an important amino acid in plants because it has a high ratio of N/C compared to other amino acids, making it an ideal nitrogen storage and transport compound (Lea et al, 2007). In relation to this feature, many important biological functions in plants have been described for asparagine such as nitrogen recycling during abiotic and biotic stresses or nitrogen mobilization and transport from source to sink tissues (Lea et al, 2007; Gaufichon et al, 2010). It was recently reported that the AK and AS genes are inversely regulated by bZIP transcription factors in Arabidopsis (Ufaz et al, 2011)
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