Characterization of the mating-type genes in Leptographium procerum and Leptographium profanum

Abstract

Highlights· The mating-type loci in Leptographium procerum and L. profanum were characterized.· The PCR-based mating-type markers were developed for these two species.· Leptographium procerum and L. profanum had a heterothallic mating system and thus these species are heterothallic. · Cryptic sexual reproduction was suggested for a population of L. procerum. AbstractLeptographium procerum and the closely related species Leptographium profanum, are ascomycetes associated with root-infesting beetles on pines and hardwood trees, respectively.Both species occur in North America where they are apparently native. Leptographium procerum has also been found in Europe, China New Zealand, and South Africa where it has most probably been introduced. As is true for many other Leptographium species, sexual states 2 have never been observed in L. procerum or L. profanum. The objectives of this study were to clone and characterize the mating type loci of these fungi, and to develop markers to determine the mating types of individual isolates. To achieve this, a partial sequence of MAT1-2-1 was amplified using degenerate primers targeting the high mobility group (HMG) sequence. A complete MAT1-2 idiomorph of L. profanum was subsequently obtained by screening a genomic library using the HMG sequence as a probe. Long range PCR was used to amplify the complete MAT1-1 idiomorph of L. profanum and both the MAT1-1 and MAT1-2 idiomorphs of L.procerum. Characterization of the MAT idiomorphs suggests that the MAT genes are fully functional and that individuals of both these species are self-sterile in nature with a heterothallic mating system. Mating type markers were developed and tested on a population of L. procerum isolates from the USA, the assumed center of origin for this species. The results suggest that cryptic sexual reproduction is occurring or has recently taken place within this population.

Mating type markers reveal high levels of heterothallism in Leptographium sensu lato

“…Based on the results of Duong et al (2013) and Tsui et al (2013), we hypothesized that many of these species might actually have heterothallic mating systems. This would explain the low level of incidence of sexual states encountered for these fungi in nature or in culture.…”

“…procerum, L. profanum (Duong et al, 2013), O. ulmi and O. novo-ulmi subsp. novo-ulmi (Paoletti et al, 2005a) were aligned and used to design primers to detect the MAT1-2 idiomorph.…”

“…These include Grosmannia clavigera and its closely related species (Tsui et al, 2013), Leptographium procerum and L. profanum (Duong et al, 2013). The MAT loci of these species have structures typical of those of heterothallic ascomycetes with both of the MAT idiomorphs present in an individual haploid genome.…”

“…The MAT1-1 idiomorphs have three mating type genes namely MAT1-1-1, MAT1-1-2 and MAT1-1-3. But notably, besides the MAT1-2-1 gene, the MAT1-2 idiomorphs, all of these species have a truncated version of MAT1-1-1, lacking the functional alpha domain (Duong et al, 2013;Tsui et al, 2013). The presence of the truncated MAT1-1-1 on the MAT1-2 idiomorph has also been noted in species of Ophiostoma (Comeau et al, 2015;Tsui et al, 2013), a sister genus of Leptographium sensu lato, suggesting that the truncation event might share an evolutionary history among these two genera and perhaps also with other genera in the Ophiostomatales.…”

Taxonomy and phylogeny of the Leptographium procerum complex, including Leptographium sinense sp. nov. and Leptographium longiconidiophorum sp. nov.

“…The identity of L. procerum in China has been confirmed using DNA sequence analyses, which also confirmed its relatedness to several other species in the genus (Lu et al 2008;2009a, b;Taerum et al 2013). In another study, Duong et al (2013) characterized the mating type genes of L. procerum and its close relative, L. profanum, showing that both species are heterothallic.…”