Characterization and transcript profiling of wood-related genes in poplar genotypes growing under salt stress conditions

The possibility of using lignocellulosic biomass produced from forest crops in order to obtain second generation biofuels is a key issue in the current context of climate change and the promotion of renewable energy sources. It is therefore important to make progress in the functional characterization of the candidate genes (CGs) associated with wood property traits relevant to this use as well as to determine the effect of different environmental factors (saline stress among others) on the expression of those genes. Populus spp. are among the forest species which rouse the most interest in the short term. Our objective is to carry out a dasometric, physiological and candidate gene expression characterization in hybrid genotypes of Populus which are suitable for use in short rotation growing under saline stress conditions.The trials were conducted under controlled greenhouse conditions. P. x canadensis ‘Oudenberg’, P. tremula x P. alba `717-1B4 ’and two autochthonous P. alba clones were tested from cuttings in individual pots. Two stress levels were applied: NaCl 68 and 137 mM, The parameters evaluated were, i) survival and expression of leaf necrosis symptoms, ii) relative height and diameter growth rate, iii) dry aerial and root biomass iiii) functional variables: net photosynthesis rate (A), stomatal conductance (gs) to infer intrinsecal water use efficiency (IWUE), and chlorophyll content. Significant interspecific differences were revealed with regard to salt stress responses, both in terms of damage symptomology and growth, production and functional variables. P. alba genotypes displayed the greatest tolerance. Transcript levels were analyzed in stem samples by Fluidigm technology for 80 selected genes related to secondary cell wall deposition (MYB and NAC transcription factors, hormone signaling, lignification, etc.). All genotypes showed changes in transcript profiles in response to salt, although the magnitude of the response was different among genotypes. About 77 % of the selected genes showed lower transcript level in plants under salt stress when compared to the salt-free treatment. The impact of salt stress on the expression of selected genes was lower in both P. alba genotypes, in agreement with the greatest tolerance.