Abstract
The pennate diatom Seminavis robusta, characterized by an archetypical diatom life cycle including a heterothallic mating system, is emerging as a model system for studying the molecular regulation of the diatom cell and life cycle. One of its main advantages compared with other diatom model systems is that sexual crosses can be made routinely, offering unprecedented possibilities for forward genetics. To date, nothing is known about the genetic basis of sex determination in diatoms. Here, we report on the construction of mating type-specific linkage maps for S. robusta, and use them to identify a single locus sex determination system in this diatom. We identified 13 mating type plus and 15 mating type minus linkage groups obtained from the analysis of 463 AFLP markers segregating in a full-sib family, covering 963.7 and 972.2 cM, respectively. Five linkage group pairs could be identified as putative homologues. The mating type phenotype mapped as a monogenic trait, disclosing the mating type plus as the heterogametic sex. This study provides the first evidence for a genetic sex determining mechanism in a diatom.
Highlights
Diatoms (Bacillariophyceae) belong to the Stramenopila, which comprise several microalgal groups dominating primary production in aquatic environments [1]
No significant difference was observed between the intervals of the 20 biparental markers in the MT+ and MT2 linkage groups, suggesting that recombination frequencies do not differ much between both mating types in S. robusta
In this study we exploit the high multiplex ratio of AFLP technology to construct the first linkage maps for a diatom species. We applied these maps to demonstrate that sex determination in the heterothallic pennate species S. robusta is genetic, and identify the sex determining region as a single locus
Summary
Diatoms (Bacillariophyceae) belong to the Stramenopila, which comprise several microalgal groups dominating primary production in aquatic environments [1]. The diatoms are one of the most diverse and productive groups of algae, with an estimated 200,000 species responsible for almost 20% of global primary production [2]. They are promising from a biotechnological point of view, and hold great potential for the production of highvalue bioproducts such as lipids, pigments and biofuels [3]. Sexual reproduction, a key feature of most diatom life cycles [7], has never been demonstrated for the most commonly used model diatoms Thalassiosira pseudonana and Phaeodactylum tricornutum [3] This prevents the use of forward genetics to link phenotype to genotype, including the use of mutagenesis and QTL mapping [8]
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