Dynamics of the Spanish fir transcriptome in nature: Metabolic pathways and gene networks involved in the response to climate stress

• Circum-Mediterranean firs are vulnerable to the effects of climate change • Identified pathways/gene networks involved in the response to environmental stress • Functional studies providing new insights for selection of best adapted genotypes Circum-Mediterranean firs, and particularly the relic Spanish-fir from the south of the Iberian Peninsula ( Abies pinsapo Boiss.), are among the most drought-sensitive and vulnerable to climate change within the broad context of Mediterranean forest species. Forest decline and die-back episodes associated to warming trends and recurrent droughts of increasing duration and intensity in the last decades point to an increasing vulnerability of A. pinsapo local populations. In this work, physiological and transcriptional analyses were combined to assess the response of trees growing in natural forests under contrasting conditions. The results show a modulation of the transcriptome in response to climatic stress with substantial changes in the expression of genes involved in water stress, aromatic amino acid metabolism, and transcription factors associated with the transcriptional regulation of the observed patterns of gene expression. Roots were determined to be the primary organs involved in the transcriptional response to stress, which may be mediated by a gene-network including interactions among structural and regulatory genes. Interactive elements comprise genes encoding stress-related proteins of the ApLEA family, ApADH, the first committed enzyme in tyrosine biosynthesis, and root-specific transcription factors implicated in stress regulation belonging to the ApERF, ApYABBY, and ApNAC superfamilies. Data provide new insights to understand the response of Spanish firs to current climatic pressure by the identification of individual genes and gene-networks potentially involved in local adaptation. This new knowledge will facilitate comparative studies of gene variation in the Spanish fir populations using the identified genes as molecular markers for the selection of the best adapted genotypes in the response to climate stress.