Pheromone Mediated Sexual Reproduction of Pennate Diatom Cylindrotheca Closterium

Abstract

Benthic diatoms dominate primary production in marine subtidal and intertidal environments. Their extraordinary species diversity and ecological success is thought to be linked with their motility and predominantly heterothallic sexual reproduction. Little is known about pheromone involvement during mating of pennate diatoms. Here we describe pheromone guided mating in the coastal raphid diatom Cylindrotheca closterium. We show that the two mating types (mt+ and mt¯) have distinct functions. Similar to other benthic diatoms, mt+ cells are searching for the mt¯ cells to pair. To enhance mating efficiency mt¯ exudes an attraction pheromone, which we proved by establishing a novel capillary assay. Further, two more pheromones produced by mt¯ promote the sexual events. One arrests the cell cycle progression of mt+ while the other induces gametogenesis of mt+. We suggest that C. closterium shares a functionally similar pheromone system with other pennate diatoms like Seminavis robusta and Pseudostaurosira trainorii which synchronize sexual events and mate attraction. Remarkably, we found no evidence of mt+ producing pheromones, which differentiates C. closterium from other pennates and suggests a less complex pheromone system in C. closterium.

The Molecular Life of Diatoms

“…Additionally, genome and transcriptomic datasets are available for both species (Basu et al 2017;Osuna-Cruz et al 2020), and P. multistriata can be transfected through biolistic transformation (Sabatino et al 2015). Meanwhile, the raphid pennate species Cylindrotheca closterium meets the requirements to become an additional model species to study life cycle regulation, including a high growth rate, the possibility of experimental cell size reduction by cell cutting to shorten generation time, frequent crossing in culture conditions, pheromone attraction assays and the availability of a draft reference genome and efficient genetic transformation protocol (Vanormelingen et al 2013;Klapper et al 2021;Belišová and Audoor et al pers. comm.…”

“…Flow cytometry showed an induction of a temporary arrest in the G1 phase of the cell cycle, which delays commitment to the meiotic or mitotic cell cycle until successful mating pair formation or a failure thereof, respectively (Moeys et al 2016;Basu et al 2017;Bilcke et al 2021a). C. closterium also employs a cytostatic sex pheromone, although pheromone production appears to be restricted to MT-, suggesting that cell cycle arresting pheromones are widespread among raphid pennate diatoms (Klapper et al 2021). On a molecular level, the cell cycle arrest is exemplified by a downregulation of the expression of mitotic cell cycle markers and, in S. robusta, genes for silica cell wall synthesis that are associated with cytokinesis (Moeys et al 2016;Basu et al 2017;Bilcke et al 2021a).…”

Decoupling cell size homeostasis in diatoms from the geometrical constraints of the silica cell-wall

“…The theory formulated by MacDonald and Pfitzer and its implications for the life history of diatoms have become a firm paradigm in the field, even though most well-known examples belong to the taxonomical group that exhibit bilateral symmetry, called pennate diatoms. A few extensively studied diatom genera, such as Seminavis, Pseudo-nitzschia and Cylindrotheca are textbook examples of the typical size reduction-restoration cycle and pheromone-induced sexuality and mating (Geitler, 1932;Chepurnov et al, 2002;D'Alelio et al, 2009;Klapper et al, 2021). Yet, it has been notably difficult to detect the expected size distribution cycles and life-cycle stages in both natural and laboratory populations of centric diatoms, which are radially symmetric (Table 1).…”