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.

Available water modifications by topsoil treatments under mediterranean semiarid conditions: afforestation plan

During dry periods in the Mediterranean area, the lack of water entering the soil matrix reduces organic contribu- tions to the soil. These processes lead to reduced soil fertility and soil vegetation recovery which creates a positive feedback process that can lead to desertification. Restoration of native vegetation is the most effective way to regenerate soil health, and control runoff and sediment yield. In Mediterranean areas, after a forestry proposal, it is highly common to register a significant number of losses for the saplings that have been introduced due to the lack of rainfall. When no vegetation is established, organic amendments can be used to rapidly protect the soil surface against the erosive forces of rain and runoff. In this study we investigated the hydrological effects of five soil treatments in relation to the temporal vari- ability of the available water for plants. Five amendments were applied in an experimental set of plots: straw mulching; mulch with chipped branches of Aleppo Pine (Pinus halepensis L.); TerraCotten hydroabsobent polymers; sewage sludge; sheep manure and control. Plots were afforested following the same spatial pattern, and amendments were mixed with the soil at the rate 10 Mg ha-1. In control plots, during June, July, August and September, soils were registered below the wilting point, and therefore, in the area of water unusable by plants. These months were coinciding with the summer mediter- ranean drought. This fact justifies the high mortality found on plants after the seeding plan. Similarly, soils have never exceeded the field capacity value measured for control plots. Conversely, in the straw and pinus mulch, soils were above the wilting point during a longer time than in control plots. Thus, the soil moisture only has stayed below the 4.2 pF suction in July, July and August. Regarding the amount of water available was also higher, especially in the months of December, January and February. However, the field capacity value measured has not showed any differences regarding the control. For these treatments, the survival sapling rates measured were the highest. Sludge, manure and polymers showed a moisture retention capacity slightly more limited than straw and pinus mulch. Likewise, it has been found that the area of usable water by plants was also lower, especially during the months of January and February. This situation is especially sharpened in plots amended with manure. In this treatment, the upper part of the soil profile was below the wilting point for six months a year (from April to August). For this treatment, the survival sapling rates measured were the lowest. In conclusion, from a land management standpoint, the pinus and straw mulch treatments have been shown as effective methods reducing water stress for plants. In this research, mulching has been proved as a significant method to reduce the mortality sapling rates during the mediterranean summer drought.

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).

The influence of organic amendments on soil aggregate stability from semiarid sites

Restoring the native vegetation is the most effective way to regenerate soil health. Under these conditions, vegetation cover in areas having degraded soils may be better sustained if the soil is amended with an external source of organic matter. The addition of organic materials to soils also increases infiltration rates and reduces erosion rates; these factors contribute to an available water increment and a successful and sustainable land management. The goal of this study was to analyze the effect of various organic amendments on the aggregate stability of soils in afforested plots. An experimental paired-plot layout was established in southern of Spain (homogeneous slope gradient: 7.5%; aspect: N170). Five amendments were applied in an experimental set of plots: straw mulching; mulch with chipped branches of Aleppo Pine (Pinus halepensis L.); TerraCotten hydroabsobent polymers; sewage sludge; sheep manure and control. Plots were afforested following the same spatial pattern, and amendments were mixed with the soil at the rate 10 Mg ha-1. The vegetation was planted in a grid pattern with 0.5 m between plants in each plot. During the afforestation process the soil was tilled to 25 cm depth from the surface. Soil from the afforested plots was sampled in: i) 6 months post-afforestation; ii) 12 months post-afforestation; iii) 18 months post-afforestation; and iv) 24 months post-afforestation. The sampling strategy for each plot involved collection of 4 disturbed soil samples taken from the surface (0–10 cm depth). The stability of aggregates was measured by wet-sieving. Regarding to soil aggregate stability, the percentage of stable aggregates has increased slightly in all the treatments in relation to control. Specifically, the differences were recorded in the fraction of macroaggregates (≥ 0.250 mm). The largest increases have been associated with straw mulch, pinus mulch and sludge. Similar results have been registered for the soil organic carbon content. Independent of the soil management, after six months, no significant differences in microaggregates were found regarding to the control plots. These results showed an increase in the stability of the macroaggregates when soil is amended with sludge, pinus mulch and straw much. This fact has been due to an increase in the number cementing agents due to: (i) the application of pinus, straw and sludge had resulted in the release of carbohydrates to the soil; and thus (ii) it has favored the development of a protective vegetation cover, which has increased the number of roots in the soil and the organic contribution to it.

Available water modifications by topsoil treatments under mediterranean semiarid conditions: afforestation plan

During dry periods in the Mediterranean area, the lack of water entering the soil matrix reduces organic contribu- tions to the soil. These processes lead to reduced soil fertility and soil vegetation recovery which creates a positive feedback process that can lead to desertification. Restoration of native vegetation is the most effective way to regenerate soil health, and control runoff and sediment yield. In Mediterranean areas, after a forestry proposal, it is highly common to register a significant number of losses for the saplings that have been introduced due to the lack of rainfall. When no vegetation is established, organic amendments can be used to rapidly protect the soil surface against the erosive forces of rain and runoff. In this study we investigated the hydrological effects of five soil treatments in relation to the temporal vari- ability of the available water for plants. Five amendments were applied in an experimental set of plots: straw mulching; mulch with chipped branches of Aleppo Pine (Pinus halepensis L.); TerraCotten hydroabsobent polymers; sewage sludge; sheep manure and control. Plots were afforested following the same spatial pattern, and amendments were mixed with the soil at the rate 10 Mg ha-1. In control plots, during June, July, August and September, soils were registered below the wilting point, and therefore, in the area of water unusable by plants. These months were coinciding with the summer mediter- ranean drought. This fact justifies the high mortality found on plants after the seeding plan. Similarly, soils have never exceeded the field capacity value measured for control plots. Conversely, in the straw and pinus mulch, soils were above the wilting point during a longer time than in control plots. Thus, the soil moisture only has stayed below the 4.2 pF suction in July, July and August. Regarding the amount of water available was also higher, especially in the months of December, January and February. However, the field capacity value measured has not showed any differences regarding the control. For these treatments, the survival sapling rates measured were the highest. Sludge, manure and polymers showed a moisture retention capacity slightly more limited than straw and pinus mulch. Likewise, it has been found that the area of usable water by plants was also lower, especially during the months of January and February. This situation is especially sharpened in plots amended with manure. In this treatment, the upper part of the soil profile was below the wilting point for six months a year (from April to August). For this treatment, the survival sapling rates measured were the lowest. In conclusion, from a land management standpoint, the pinus and straw mulch treatments have been shown as effective methods reducing water stress for plants. In this research, mulching has been proved as a significant method to reduce the mortality sapling rates during the mediterranean summer drought.