Restructuring of Holocentric Centromeres During Meiosis in the Plant Rhynchospora pubera

Abstract

Centromeres are responsible for the correct segregation of chromosomes during mitosis and meiosis. Holocentric chromosomes, characterized by multiple centromere units along each chromatid, have particular adaptations to ensure regular disjunction during meiosis. Here we show by detecting CENH3, CENP-C, tubulin, and centromeric repeats that holocentromeres may be organized differently in mitosis and meiosis of Rhynchospora pubera. Contrasting to the mitotic linear holocentromere organization, meiotic centromeres show several clusters of centromere units (cluster-holocentromeres) during meiosis I. They accumulate along the poleward surface of bivalents where spindle fibers perpendicularly attach. During meiosis II, the cluster-holocentromeres are mostly present in the midregion of each chromatid. A linear holocentromere organization is restored after meiosis during pollen mitosis. Thus, a not yet described case of a cluster-holocentromere organization, showing a clear centromere restructuration between mitosis and meiosis, was identified in a holocentric organism.KEYWORDS holocentric chromosomes; CENH3; CENP-C; centromere structure/organization; inverted meiosis T HE centromere is the chromosome site responsible for spindle fiber attachment and faithful chromosome segregation during mitosis and meiosis. In general, every eukaryotic chromosome has a centromere on which the kinetochore complex assembles (Cleveland et al. 2003;Burrack and Berman 2012). In most eukaryotes, centromeric nucleosomes contain CENH3 (also known as CENP-A, a histone H3 variant that replaces canonical H3 at the centromere), and usually spans several hundred kilobase pairs often in association with centromere-specific repeats (Steiner and Henikoff 2015).Centromere organization and dynamics vary between mitosis and meiosis (Duro and Marston 2015;Ohkura 2015). During mitosis, sister chromatids are held together by centromere cohesion until metaphase. Simultaneous with the disruption of cohesion, sister chromatids are pulled to opposite poles during anaphase. In contrast, during meiosis, sister centromere cohesion is ensured until metaphase II (Ishiguro and Watanabe 2007). The stepwise regulation of cohesion release during meiosis I (MI) and II (MII) is well studied in organisms with one primary constriction per chromosome (monocentric), ensuring the segregation of homologs at MI followed by the segregation of sister chromatids at MII (Duro and Marston 2015).Contrary to monocentrics, the centromeres of holocentric chromosomes are distributed almost over the entire chromosome length and cohesion occurs along the entire associated sister chromatids (Maddox et al. 2004). Although this does not imply much difference during mitotic divisions, the presence of a holokinetic centromere (holocentromere) imposes obstacles to the dynamics of chromosome segregation in meiosis. Due to their alternative chromosome organization, species with holocentric chromosomes cannot perform the two-step cohesion loss during meiosis typical for monocentric species...

Unequal contribution of two paralogous centromeric histones to function the cowpea centromere

“…CENPC is a conserved component of most eukaryotic centromeres that links the inner and outer (microtubule-binding) components of the kinetochore (Earnshaw 2015). CENPC co-localizes with CENH3, defining active centromere chromatin (Marques et al 2016; Falk et al 2015; Kato et al 2013; Carroll et al 2010). A single CENPC candidate ( Vu CENPC, Transcript ID: Vigun05g287700) was identified in the cowpea genome which aligned with CENPC sequences found in other species (Supplemental Figure 5a).…”

Unequal contribution of two paralogous CENH3 variants in cowpea centromere function

“…CENPC is a conserved component of most eukaryotic centromeres that links the inner and outer (microtubule-binding) components of the kinetochore 19 . CENPC co-localizes with CENH3, defining active centromere chromatin [20][21][22][23] . A single CENPC candidate (VuCENPC, Transcript ID: Vigun05g287700) was identified in the cowpea genome which aligned with CENPC sequences found in other species ( Supplementary Fig.…”

Inverted meiosis and the evolution of sex by loss of complementation

“…Suppression of the second (a, b) or first (c, d) division, without recombination (a, c) or with one crossing over (b, d). In case b, segregation can be of two types: z and x (z is more common) Suppression of the second division requires further analysis because, in inverted meiosis, there is evidence for a bias in favour of z segregation (because chromatids pair with each other more likely than with the sister chromatid with which there was no chiasma, perhaps because they are in close proximity and remain linked at their termini by chromatin threads (Cabral et al, 2014, Marques, Schubert, Houben, & Pedrosa-Harand, 2016). A recent study (Yin et al, 2019) shows that in inverted meiosis in mouse the z type is much more likely (up to two orders of magnitude) than the x type.…”