Chromosomal Characterization of the Three Subgenomes in the Polyploids of Hordeum murinum L.: New Insight into the Evolution of This Complex

Abstract

Hordeum murinum L. is a species complex composed of related taxa, including the subspecies glaucum, murinum and leporinum. However, the phylogenetic relationships between the different taxa and their cytotypes, and the origin of the polyploid forms, remain points of controversy. The present work reports a comparative karyotype analysis of seven accessions of the H. murinum complex representing all subspecies and cytotypes. The karyotypes were determined by examining the distribution of the repetitive Triticeae DNA sequences pTa71, pTa794, pSc119.2, pAs1 and pHch950, the simple sequence repeats (SSRs) (AG)10, (AAC)5, (AAG)5, (ACT)5, (ATC)5, and (CCCTAAA)3 via in situ hybridization. The chromosomes of the three subgenomes involved in the polyploids were identified. All tetraploids of all subspecies shared the same two subgenomes (thus suggesting them to in fact belong to the same taxon), the result of hybridization between two diploid ancestors. One of the subgenomes present in all tetraploids of all subspecies was found to be very similar (though not identical) to the chromosome complement of the diploid glaucum. The hexaploid form of leporinum came about through a cross between a tetraploid and a third diploid form. Exclusively bivalent associations among homologous chromosomes were observed when analyzing pollen mother cells of tetraploid taxa. In conclusion, the present results identify all the individual chromosomes within the H. murinum complex, reveal its genome structure and phylogeny, and explain the appearance of the different cytotypes. Three cryptic species are proposed according to ploidy level that may deserve full taxonomic recognition.

Chromosomal organization of repetitive DNAs in Hordeum bogdanii and H. brevisubulatum (Poaceae)

“…In addition, the genomic constitution of Hordeum murinum was characterized using multiple repetitive sequences. The results identified all the individual chromosomes within the Hordeum murinum complex, elucidated its genomic structure and phylogeny, and explained the appearance of different cytotypes (Cuadrado et al 2013). Thus far, detailed information on the chromosome organization of multiple repetitive sequences is available for the H, Xa, and Xu genomes.…”

“…The pSc119.2 repeat produced sub-telomeric signals on nearly all chromosomes in Hordeum marinum (Taketa et al 2000); however, fewer of these signals were present in Hordeum bogdanii . Karyotype analysis of diploid Hordeum murinum (Xu) showed that AG produced intense signals around the centromere in four chromosome pairs and that AAG produced more rich and intense signals than AAC, ACT, and CAT in pericentromeric regions (Cuadrado et al 2013, Carmona et al 2013b). In addition, no pSc119.2 hybridization signals were detected in diploid Hordeum murinum (Taketa et al 2000).…”

Satellite DNA in Plants: More than Just Rubbish

“…This suggests that satellite arrays undergo rapid evolution through both expansion and shrinkage, resulting in the replacement of the most abundant variant with a different variant [Melters et al, 2013;Zhang et al, 2013b]. Simple sequence repeats are also commonly found forming pericentromeric heterochromatin [Hudakova et al, 2001;Cuadrado and Jouve, 2007;Carmona et al, 2013a;Cuadrado et al, 2013]. In addition to satellite DNA families, centromeric retrotransposons represent an important component of centromeres of a wide range of angiosperm species, implying these families are the key to plant centromere evolution and function .…”

Evidencia de autopoliploidía y translocaciones en el cariotipo de Tigridia pavonia (Iridaceae, Iridoideae) de la Reserva Ecológica del Pedregal de San Ángel, México

“…En contraparte, las plantas de origen alopoliploide experimentan inactivación de las regiones NOR de uno de los genomas parentales, silenciadas por efecto de dominancia nucleolar y en consecuencia se registra un número menor de satélites. Así, en el complejo Hordeum murinum L. (Poaceae, Triticeae) los citotipos tetraploides y hexaploides surgidos por hibridación exhiben únicamente un par de cromosomas con constricciones secundarias y satélites (Cuadrado et al, 2013). De hecho, la inactivación de genes ribosomales es uno de los fenómenos más comunes en miembros híbridos y poliploides de Triticeae (Cermeño y Lacadena, 1985;Carmona et al, 2016).…”