Transcriptional regulation os phenylalaline biosynthesis and utilization

Conifer trees divert large quantities of carbon into the biosynthesis of phenylpropanoids, particularly to generate lignin, an important constituent of wood. Since phenylalanine is the precursor for phenylpropanoid biosynthesis, the precise regulation of phenylalanine synthesis and utilization should occur simultaneously. This crucial pathway is finely regulated primarily at the transcriptional level. Transcriptome analyses indicate that the transcription factors (TFs) preferentially expressed during wood formation in plants belong to the MYB and NAC families. Craven-Bartle et al. (2013) have shown in conifers that Myb8 is a candidate regulator of key genes in phenylalanine biosynthesis involved in the supply of the phenylpropane carbon skeleton necessary for lignin biosynthesis. This TF is able to bind AC elements present in the promoter regions of these genes to activate transcription. Constitutive overexpression of Myb8 in white spruce increased secondary-wall thickening and led to ectopic lignin deposition (Bomal et al. 2008). In Arabidopsis, the transcriptional network controlling secondary cell wall involves NAC-domain regulators operating upstream Myb transcription factors. Functional orthologues of members of this network described have been identified in poplar and eucalyptus, but in conifers functional evidence had only been obtained for MYBs. We have identified in the P. pinaster genome 37 genes encoding NAC proteins, which 3 NAC proteins could be potential candidates to be involved in vascular development (Pascual et al. 2015). The understanding of the transcriptional regulatory network associated to phenylpropanoids and lignin biosynthesis in conifers is crucial for future applications in tree improvement and sustainable forest management. This work is supported by the projects BIO2012-33797, BIO2015-69285-R and BIO-474 References: Bomal C, et al. (2008) Involvement of Pinus taeda MYB1 and MYB8 in phenylpropanoid metabolism and secondary cell wall biogenesis: a comparative in planta analysis. J Exp Bot. 59: 3925-3939. Craven-Bartle B, et al. (2013) A Myb transcription factor regulates genes of the phenylalanine pathway in maritime pine. Plant J, 74: 755-766. Pascual MB, et al. (2015) The NAC transcription factor family in maritime pine (Pinus pinaster): molecular regulation of two genes involved in stress responses. BMC Plant Biol, 15: 254.

Ammonium uptake, transport and nitrogen economy in forest trees

AMMONIUM UPTAKE, TRANSPORT AND NITROGEN ECONOMY IN FOREST TREES Francisco M. Cánovas, Concepción Avila, Fernando N. de la Torre, Rafael A. Cañas, Belén Pascual, Vanessa Castro- Rodríguez, Jorge El-Azaz Departamento de Biología Molecular y Bioquímica, Facultad de Ciencias, Universidad de Málaga, Spain. Email: canovas@uma.es Forests ecosystems play a fundamental role in the regulation of global carbon fixation and preservation of biodiversity. Forest trees are also of great economic value because they provide a wide range of products of commercial interest, including wood, pulp, biomass and important secondary metabolites. The productivity of most forest ecosystems is limited by low nitrogen availability and woody perennials have developed adaptation mechanisms, such as ectomycorrhizal associations, to increase the efficiency of N acquisition and metabolic assimilation. The efficient acquisition, assimilation and economy of nitrogen are of special importance in trees that must cope with seasonal periods of growth and dormancy over many years. In fact, the ability to accumulate nitrogen reserves and to recycle N is crucial to determine the growth and production of forest biomass. Ammonium is the predominant form of inorganic nitrogen in the soil of temperate forests and many research efforts are addressed to study the regulation of ammonium acquisition, assimilation and internal recycling for the biosynthesis of amino acids, particularly those relevant for nitrogen storage. In our laboratory, we are interested in studying nitrogen metabolism and its regulation in maritime pine (Pinus pinaster L. Aiton), a conifer species of great ecological and economic importance in Europe and for which whole-transcriptome resources are available. The metabolism of phenylalanine plays a central role in the channeling of carbon from photosynthesis to the biosynthesis of phenylpropanoids and the regulation of this pathway is of broad significance for nitrogen economy of maritime pine. We are currently exploring the molecular properties and regulation of genes involved in the biosynthesis and metabolic fates of phenylalanine in maritime pine. An overview of this research programme will be presented and discussed. Research supported by Spanish Ministry of Economy and Competitiveness and Junta de Andalucía (Grants BIO2015-69285-R, BIO2012-0474 and research group BIO-114).

NAC-MYB basedtranscriptional networkinvolved in the regulation of phenylalanine biosynthesis in P. pinaster

P2-2 NAC-MYB-BASED TRANSCRIPCIONAL NETWORK INVOLVED IN THE REGULATION OF PHENYLALANINE BIOSYNTHESIS IN P. PINASTER Mª Belén Pascual, Rafael A. Cañas, Blanca Craven-Bartle, Francisco M. Cánovas and Concepción Ávila Departamento de Biología Molecular y Bioquímica. Facultad de Ciencias. Universidad de Málaga. Campus de teatinos s/n, Málaga, Spain Email: cavila@uma.es Conifer trees divert large quantities of carbon into the biosynthesis of phenylpropanoids, particularly to generate lignin, an important constituent of wood. Since phenylalanine is the precursor for phenylpropanoid biosynthesis, the precise regulation of phenylalanine synthesis and use should occur simultaneously. This crucial pathway is finely regulated primarily at the transcriptional level. Transcriptome analyses indicate that the transcription factors (TFs) preferentially expressed during wood formation in plants belong to the MYB and NAC families. Craven-Bartle et al. (2013) have shown that Myb8 is a candidate regulator of key genes in phenylalanine biosynthesis involved in the supply of the phenylpropane carbon skeleton necessary for lignin biosynthesis. This TF is able to bind AC elements present in the promoter regions of these genes to activate transcription. In Arabidopsis, the transcriptional network controlling secondary cell wall involves NAC-domain regulators operating upstream Myb transcription factors. We have identified in the P. pinaster genome three NAC proteins as potential candidates to be involved in vascular development. One of them, PpNAC1 is expressed both in xylem and compression wood from adult trees and has been thoroughly characterized. Its role upstream the transcriptional network involving Myb8 will be discussed. The understanding of the transcriptional regulatory network associated to phenylpropanoids and lignin biosynthesis in conifers is crucial for future applications in tree improvement and sustainable forest management.