Caracterización citogenética y molecular de los extremos cromosómicos implicados en procesos de reconocimiento y asociación durante la meiosis en trigo y cebada

Homologous chromosome recognition and pairing during meiosis is essential for the formation of viable gametes, a particularly complex process in polyploid cereals such as bread wheat (Triticum aestivum; 2n=6x=42) and durum wheat (T. turgidum; 2n=4x=28) due to the coexistence of different subgenomes. This PhD thesis demonstrates that telomeric and subtelomeric regions, traditionally considered merely structural, play a crucial role as dynamic centres of chromosomal identity and for homologous recognition initiation, as they contain essential repeated elements that facilitate this process. The existence of a molecular “barcode” at chromosome ends regulating homologous association is revealed, showing that telomeres and subtelomeres exhibit far greater structural variability than expected and function as active regions of chromatin remodelling, whose understanding facilitates the development of genetic improvement strategies in wheat. Analysis of the satellitome in cultivated species and wild relatives shows that satellite DNA (satDNA) is preferentially located in subtelomeric regions and is organized into multiple specific families that confer chromosomal identity and serve as valuable molecular and cytogenetic markers. The identification of these satDNA families in the species analysed has enabled the construction of an integrated physical map that provides a key tool for genomic studies and breeding programs. Comparison of the satellitome between bread wheat and durum wheat reveals divergences, rapid expansions, and contractions in these sequences within less than 8,000 years, highlighting the impact of domestication and selection and supporting the hypothesis that they contribute to defining chromosome identity and species specificity. Likewise, the study of the satellitome in agronomically valuable barleys (Hordeum chilense and H. vulgare) has identified 46 families grouped into 36 homology groups with divergent profiles confirming the existence of differentiated genetic lineages, and also describes pericentromeric satellites that provide centromere plasticity and highly variable subtelomeric satellites, whose diversity supports their participation in homologous chromosome recognition and association. Overall, this work demonstrates that chromosome terminal regions are highly dynamic, variable, and chromosome-, subgenome-, and species-specific, acting as key nodes for the regulation of chromosomal associations during meiosis and containing molecular parameters such as G-quadruplexes, GC content, CpG islands, and mobile elements that define a chromosomal “barcode.” The adaptive diversity of satellite DNA and its interaction with transposable elements reflect recent reorganizations associated with the evolution and domestication of wheat and barley studied, providing fundamental insights to understand homologous recognition mechanisms, optimize interspecific crosses, and implement more precise and efficient breeding strategies in cereals with complex genomes.