Latitudinal Variation in the Toxicity and Sexual Compatibility of Alexandrium catenella Strains from Southern Chile

The bloom-forming toxic dinoflagellate Alexandrium catenella was first detected in southern Chile (39.5–55° S) 50 years ago and is responsible for most of the area’s cases of paralytic shellfish poisoning (PSP). Given the complex life history of A. catenella, which includes benthic sexual cysts, in this study, we examined the potential link between latitude, toxicity, and sexual compatibility. Nine clones isolated from Chilean Patagonia were used in self- and out-crosses in all possible combinations (n = 45). The effect of latitude on toxicity, reproductive success indexes, and cyst production was also determined. Using the toxin profiles for all strains, consisting of C1, C2, GTX4, GTX1, GTX3, and NeoSTX, a latitudinal gradient was determined for their proportions (%) and content per cell (pg cell−1), with the more toxic strains occurring in the north (−40.6° S). Reproductive success also showed a latitudinal tendency and was lower in the north. None of the self-crosses yielded resting cysts. Rather, the production of resting cysts was highest in pairings of clones separated by distances of 1000–1650 km. Our results contribute to a better understanding of PSP outbreaks in the region and demonstrate the importance of resting cysts in fueling new toxic events. They also provide additional evidence that the introduction of strains from neighboring regions is a cause for concern.

Latitudinal Variation in the Toxicity and Sexual Compatibility of Alexandrium catenella Strains From Southern Chile

The bloom-forming toxic dinoflagellate Alexandrium catenella was first detected in Southern Chile (39.5–55°S) 50 years ago and is responsible for most of the area’s cases of paralytic shellfish poisoning (PSP). Given the complex life history of A. catenella, which includes benthic sexual cysts, in this study we examined the potential link between latitude, toxicity, and sexual compatibility. Nine clones isolated from Chilean Patagonia were used in self- and out-crosses in all possible combinations (n=45). The effect of latitude on toxicity, reproductive success indexes, and cyst production was also determined. Although the toxin profiles were similar for all strains, consisting of C1, C2, GTX4, GTX1, GTX3, and NeoSTX, a latitudinal gradient was determined for their proportions (%) and content per cell (pg cell−1), with the more toxic strains occurring in the north (−40.6°S). Reproductive success also showed a latitudinal tendency and was lower in the north. None of the self-crosses yielded resting cysts. Rather, the production of resting cysts was highest in pairings of clones separated by distances of 1000–1650km. Our results contribute to a better understanding of PSP outbreaks in the region and demonstrate the importance of resting cysts in fueling new toxic events. They also provide additional evidence that the introduction of strains from neighboring regions is a cause for concern.

Mating-Type Locus Organization and Mating-Type Chromosome Differentiation in the Bipolar Edible Button Mushroom Agaricus bisporus

In heterothallic basidiomycete fungi, sexual compatibility is restricted by mating types, typically controlled by two loci: PR, encoding pheromone precursors and pheromone receptors, and HD, encoding two types of homeodomain transcription factors. We analysed the single mating-type locus of the commercial button mushroom variety, Agaricus bisporus var. bisporus, and of the related variety burnettii. We identified the location of the mating-type locus using genetic map and genome information, corresponding to the HD locus, the PR locus having lost its mating-type role. We found the mip1 and β-fg genes flanking the HD genes as in several Agaricomycetes, two copies of the β-fg gene, an additional HD2 copy in the reference genome of A. bisporus var. bisporus and an additional HD1 copy in the reference genome of A. bisporus var. burnettii. We detected a 140 kb-long inversion between mating types in an A. bisporus var. burnettii heterokaryon, trapping the HD genes, the mip1 gene and fragments of additional genes. The two varieties had islands of transposable elements at the mating-type locus, spanning 35 kb in the A. bisporus var. burnettii reference genome. Linkage analyses showed a region with low recombination in the mating-type locus region in the A. bisporus var. burnettii variety. We found high differentiation between β-fg alleles in both varieties, indicating an ancient event of recombination suppression, followed more recently by a suppression of recombination at the mip1 gene through the inversion in A. bisporus var. burnettii and a suppression of recombination across whole chromosomes in A. bisporus var. bisporus, constituting stepwise recombination suppression as in many other mating-type chromosomes and sex chromosomes.