Centromeres are rapidly evolving across eukaryotes, despite performing a conserved function to ensure high-fidelity chromosome segregation. CENP-A chromatin is a hallmark of a functional centromere in most organisms. Due to its critical role in kinetochore architecture, the loss of CENP-A is tolerated in only a few organisms, many of which possess holocentric chromosomes. Here, we characterize the consequence of the loss of CENP-A in the fungal kingdom. Mucor circinelloides, an opportunistic human pathogen, lacks CENP-A along with the evolutionarily conserved CENP-C but assembles a monocentric chromosome with a localized kinetochore complex throughout the cell cycle. Mis12 and Dsn1, two conserved kinetochore proteins, were found to co-localize to a short region, one in each of nine large scaffolds, composed of an ∼200-bp AT-rich sequence followed by a centromere-specific conserved motif that echoes the structure of budding yeast point centromeres. Resembling fungal regional centromeres, these core centromere regions are embedded in large genomic expanses devoid of genes yet marked by Grem-LINE1s, a novel retrotransposable element silenced by the Dicer-dependent RNAi pathway. Our results suggest that these hybrid features of point and regional centromeres arose from the absence of CENP-A, thus defining novel mosaic centromeres in this early-diverging fungus.

Summary: Light regulates many developmental and physiological processes in a large number of organisms. The best‐known light response in the fungus Mucor circinelloides is the biosynthesis of β‐carotene. Here, we show that M. circinelloides sporangiophores also respond to light, exhibiting a positive phototropism. Analysis of both responses to different light wavelengths within the visible spectrum demonstrated that phototropism is induced by green and blue light, whereas carotenogenesis is only induced by blue light. The blue regulation of both responses suggests the existence of blue‐light photoreceptors in M. circinelloides. Three white collar‐1 genes (mcwc‐1a, mcwc‐1b and mcwc‐1c) coding for proteins showing similarity with the WC‐1 photoreceptor of Neurospora crassa have been identified. All three contain a LOV (light, oxygen or voltage) domain, similar to that present in fungal and plant blue‐light receptors. When knockout mutants for each mcwc‐1 gene were generated to characterize gene functions, only mcwc‐1c mutants were defective in light induction of carotene biosynthesis, indicating that mcwc‐1c is involved in the light transduction pathway that control carotenogenesis. We have also shown that positive phototropism is controlled by the mcwc‐1a gene. It seems therefore that mcwc‐1a and mcwc‐1c genes control different light transduction pathways, although cross‐talk between both pathways probably exists because mcwc‐1a is involved in the light regulation of mcwc‐1c expression.