IS THE HOLOCENTROMERE OF CLADIUM MARISCUS (CYPERACEAE) BASED ON SATELLITE REPEATS?

SADER M. A.; MARQUES A.; KUO YI-TZU ; SCHUBERT V; FUCHS J; PISTRICK K; HOUBEN A; PEDROSA-HARAND, A. (ANDREA PEDROSA-HARAND)

Ouro Preto

Congreso; 68th Brazilian Congress of Genetics; 2023

Sociedade Brasileira de Genética

While most species are monocentric, with a centromere restricted to a single region per chromosome, some organisms possess holocentromeres, in which the centromere activity is distributed over the entire chromosome length. This transition occurred independently at least 13 times across distant plant and animal families. Among plants, the family Cyperaceae (sedges) comprises species with holocentric chromosomes. However, whether all species within the family are holocentric is still unknown. Here we investigated the genome and chromosome organization in the great fen sedge, Cladium mariscus (L.) Pohl, one of the first species diverging within the large subfamily Cyperoideae. It has 2n = 72 chromosomes with a unknown centromere structure, and a small genome size (2C = 0.565 pg). We combined different approaches such as repetitive genome fraction analysis using Repeat Explorer, fluorescence in situ hybridization (FISH), and indirectimmunostaining for kinetochore proteins. The repeatome (13.7% of the genome) of C. mariscus contains mainly a high proportions of satellite DNAs (2.45%) followed by LTR-retrotransposons from Ty1/copiaAngela (0.57%) and Ty3/gypsy-Athila (0.39%) clades. The most abundant satellites, CmaSat1-92, and CmaSat2-172, were mapped to mitotic chromosomes, with CmaSat1-92 distributed along each chromatid from telomere to telomere, while CmaSat2-172 showed a dot-like distribution where CmaSat1-92 was absent. The CmaSat1-92 signals colocalized with kinetochore proteins (KnL1) detected by immunostaining as a line along each chromatid. Altogether, it seems that C. mariscus has likely satellite-based, small holocentric chromosomes. Our data suggest that the transition to holocentricity occurred early during the Cyperaceae diversification.