Identificación de genes asociados a la capacidad de embriogénesis somática en Pinus pinea L

Abstract

Somatic embryogenesis is a process of adventitious regeneration by which already differentiated somatic plant cells enter a new cell cycle and acquire full capacity to form embryos that can give rise to a complete adult plant. Although this process can occur naturally, the induction of somatic embryogenesis under controlled conditions is limiting in certain plant species, especially in forest tree species. In general, the genus Pinus is still considered to be recalcitrant to the induction of somatic embryogenesis. The stone pine (Pinus pinea L.) is a natural conifer that is widespread throughout the Mediterranean strip and is known for production of pine nuts, one of the most important forest products. The stone pine is propagated vegetatively, mainly by grafting. However, variability in production, due to scion-rootstock interaction and its seasonal limitations, is a major disadvantage. Somatic embryogenesis allows the production of large number of plants, as well as the possibility of long-term conservation of embryogenic lines for the development of a silviculture of tested forest varieties. However, factors affecting the expression of embryogenic capacity, mainly genotype, limit the extensive use of this technology. Nowadays, the availability of large-scale analysis techniques has opened the possibility of defining groups of genes, proteins and metabolites that are expressed simultaneously associated with numerous tree development processes and, therefore, to be transferred to breeding programs for a more accurate diagnosis and characterization of the reproductive materials used that will allow individualized management after diagnosis. In this work we have identified and characterized genes related to the genotype-associated somatic embryogenesis capacity in Pinus pinea L. The global analysis of gene expression in lines of genotypes with high and low embryogenic capacity indicates that numerous regulatory pathways, either induced or repressed in a coordinated manner with putative target genes, are significantly modulated during the induction or repression of somatic embryogenesis. Chromatin remodeling-dependent epigenetic regulation and miRNAmediated regulation, as well as expression of genes with recognized function in somatic embryogenesis are relevant and may indicate that masses of lines with low embryogenic capacity may respond to culture conditions and express or induce some competence for embryogenesis, with other factors inhibiting their full expression. Although these masses express competence for initiation of cell division, cell cycle progression and the establishment of meristematic identity do not progress. Auxin, jasmonate and brassinosteroid signaling pathways along with cell wall, membrane and cytoskeleton mediated signaling would represent activators or repressors of transcription of target genes associated with embryogenic capacity, such as those encoding for transcription factors with documented function in the process. The expression of genes encoding for proteins involved in the differentiation of adult tissues, in the organization of the cytoskeleton and certain transcription factors in the masses of lines with low embryogenic capacity and in vegetative organs could indicate the expression of a potential inhibition of cell reprogramming or of the embryogenic competence, probably associated with the dynamics of the cytoskeleton and the irreversible induction of differentiation processes in these masses related to a loss of embryogenic competence.