Distinct patterns of satDNA distribution in holocentric chromosomes of spike-sedges (Eleocharis, Cyperaceae).

Abstract

Eleocharis R. Br. (Cyperaceae) species are known for having holocentric chromosomes, which enable rapid karyotype differentiation. High intra- and interspecific variations in chromosome numbers and genome sizes are documented for different Eleocharis species, frequently accompanied by fluctuations in the repetitive DNA fraction. However, a lack of detailed analysis has hampered a better understanding of the interplay between holocentricity and repetitive DNA evolution in this genus. In our study, we confirmed the holocentricity of Eleocharis chromosomes by immunostaining against the kinetochore protein KNL1 and the cell-cycle dependent posttranslational modifications histone H2AThr121ph and H3S10ph. We further studied the composition and chromosomal distribution of the main satellite DNA repeats found in the newly sequenced species E. maculosa, E. geniculata, E. parodii, E. elegans, and E. montana. Five of the six satellites discovered were arranged in clusters, while EmaSAT14 was distributed irregularly along the chromatid length in a line-like manner. EmaSAT14 monomers were present in a few copies in few species across the Eleocharis phylogenetic tree. Nonetheless, they were accumulated within a restricted group of Maculosae series, subgenus Eleocharis. The data indicates that the amplification and line-like distribution of EmaSAT14 along chromatids may have occurred recently within a section of the genus.