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Forest trees have access to diverse nitrogenous compounds in the soil such as ammonium, nitrate and amino acids. Recent progress has been made in the identification and characterization of ammonium and nitrate transporters. However, much more limited is our current knowledge of amino acid transport systems despite their relevance to fully understanding nitrogen nutrition in trees. In the present study, we have identified 10 genes encoding putative amino acid permeases of the AAP family in maritime pine (Pinus pinaster Ait.). Four members of this family, PpAAP1, PpAAP2, PpAAP3 and PpAAP4 were phylogenetically related to AtAAP5, involved in arginine transport in Arabidopsis thaliana. One of these genes, PpAAP1 , exhibited enhanced expression levels in maritime pine roots when arginine was externally supplied. PpAAP1 was functionally characterized by complementation of a yeast mutant strain defective in the transport of arginine, allowing yeast to take up [14C]-arginine with high affinity. Furthermore, PpAAP1 was able to restore the severely affected root uptake of arginine displayed by AtAAP5 T-DNA mutants. Uptake rates of 15N-labelled arginine were significantly higher in PpAAP1 -overexpressing plants when compared to wild-type and AtAAP5 mutant plants. Taken together, our results indicate that PpAAP1 is a high-affinity arginine transporter in maritime pine. [ABSTRACT FROM AUTHOR]

Cytosolic NADP+-isocitrate dehydrogenase (ICDH) is one of the major enzymes involved in the production of 2-oxoglutarate for amino acid biosynthesis in plants. In most plants studied, ICDH is encoded by either one gene or a small gene family, and the protein sequence has been highly conserved during evolution, suggesting it plays different and essential roles in metabolism and differentiation. To elucidate the role of ICDH in hybrid poplar (Populus tremula x P. alba), transgenic plants overexpressing the Pinus pinaster gene were generated. Overexpression of ICDH resulted in hybrid poplar (Populus tremula x P. alba) trees with higher expression levels of the endogenous ICDH gene and higher enzyme content than control untransformed plants. Transgenic poplars also showed an increased expression of glutamine synthetase (GS1.3), glutamate decarboxylase (GAD) and other genes associated with vascular differentiation. Furthermore, these plants exhibited increased growth in height, longer internodes and enhanced vascular development in young leaves and the apical region of stem. Modifications in amino acid and organic acid content were observed in young leaves of the transgenic lines, suggesting an increased biosynthesis of amino acids for building new structures and also for transport to other sink organs, as expanding leaves or young stems. Taken together, these results support an important role of ICDH in plant growth and vascular development. [ABSTRACT FROM AUTHOR]

Summary: The transcriptional regulation of phenylalanine metabolism is particularly important in conifers, long‐lived species that use large amounts of carbon in wood. Here, we show that the Pinus pinaster transcription factor, PpNAC1, is a main regulator of phenylalanine biosynthesis and utilization. A phylogenetic analysis classified PpNAC1 in the NST proteins group and was selected for functional characterization. PpNAC1 is predominantly expressed in the secondary xylem and compression wood of adult trees. Silencing of PpNAC1 in P. pinaster results in the alteration of stem vascular radial patterning and the down‐regulation of several genes associated with cell wall biogenesis and secondary metabolism. Furthermore, transactivation and EMSA analyses showed that PpNAC1 is able to activate its own expression and PpMyb4 promoter, while PpMyb4 is able to activate PpMyb8, a transcriptional regulator of phenylalanine and lignin biosynthesis in maritime pine. Together, these results suggest that PpNAC1 is a functional ortholog of the ArabidopsisSND1 and NST1 genes and support the idea that key regulators governing secondary cell wall formation could be conserved between gymnosperms and angiosperms. Understanding the molecular switches controlling wood formation is of paramount importance for fundamental tree biology and paves the way for applications in conifer biotechnology. [ABSTRACT FROM AUTHOR]

• In the present work the performance of transgenic poplars expressing a pine glutamine synthetase (GS) transgene was studied in natural conditions. • A field study of eight independent transgenic lines and control plants was carried out for 3 yr in the province of Granada (Spain). • Transgenic poplars reached average heights that were 21, 36 and 41% greater than control plants after the first, second and third year of growth, respectively. Transgene expression affected plant features with time resulting in increased protein, total GS and ferredoxin-dependent glutamate synthase (Fd-GOGAT) in leaves. However, neither differences in the large subunit of Rubisco (LSU) abundance nor water content were detected between lines. Furthermore, no significant differences were found in total polysaccharide and lignin content in tree trunks. • The analyses of stem diameter, and protein contents in the bark suggest that higher levels of nitrogen reserves accumulated in the stem of transgenics. Our results suggest that modification of GS1 expression may be a useful strategy to complement traditional tree breeding in short rotation plantations. New Phytologist (2004) doi: 10.1111/j.1469-8137.2004.01173.x © New Phytologist (2004) [ABSTRACT FROM AUTHOR]

Forest trees have access to diverse nitrogenous compounds in the soil such as ammonium, nitrate and amino acids. Recent progress has been made in the identification and characterization of ammonium and nitrate transporters. However, much more limited is our current knowledge of amino acid transport systems despite their relevance to fully understanding nitrogen nutrition in trees. In the present study, we have identified 10 genes encoding putative amino acid permeases of the AAP family in maritime pine (Pinus pinaster Ait.). Four members of this family, PpAAP1, PpAAP2, PpAAP3 and PpAAP4 were phylogenetically related to AtAAP5, involved in arginine transport in Arabidopsis thaliana. One of these genes, PpAAP1, exhibited enhanced expression levels in maritime pine roots when arginine was externally supplied. PpAAP1 was functionally characterized by complementation of a yeast mutant strain defective in the transport of arginine, allowing yeast to take up [14C]-arginine with high affinity. Furthermore, PpAAP1 was able to restore the severely affected root uptake of arginine displayed by AtAAP5 T-DNA mutants. Uptake rates of 15N-labelled arginine were significantly higher in PpAAP1-overexpressing plants when compared to wild-type and AtAAP5 mutant plants. Taken together, our results indicate that PpAAP1 is a high-affinity arginine transporter in maritime pine., (© The Author(s) 2021. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permission@oup.com.)

The transcriptional regulation of phenylalanine metabolism is particularly important in conifers, long-lived species that use large amounts of carbon in wood. Here, we show that the Pinus pinaster transcription factor, PpNAC1, is a main regulator of phenylalanine biosynthesis and utilization. A phylogenetic analysis classified PpNAC1 in the NST proteins group and was selected for functional characterization. PpNAC1 is predominantly expressed in the secondary xylem and compression wood of adult trees. Silencing of PpNAC1 in P. pinaster results in the alteration of stem vascular radial patterning and the down-regulation of several genes associated with cell wall biogenesis and secondary metabolism. Furthermore, transactivation and EMSA analyses showed that PpNAC1 is able to activate its own expression and PpMyb4 promoter, while PpMyb4 is able to activate PpMyb8, a transcriptional regulator of phenylalanine and lignin biosynthesis in maritime pine. Together, these results suggest that PpNAC1 is a functional ortholog of the ArabidopsisSND1 and NST1 genes and support the idea that key regulators governing secondary cell wall formation could be conserved between gymnosperms and angiosperms. Understanding the molecular switches controlling wood formation is of paramount importance for fundamental tree biology and paves the way for applications in conifer biotechnology., (© 2017 The Authors. Plant Biotechnology Journal published by Society for Experimental Biology and The Association of Applied Biologists and John Wiley & Sons Ltd.)