The PaAlr1 magnesium transporter is required for ascospore development in Podospora anserina

The Hot QTL Locations for Potassium, Calcium, and Magnesium Nutrition and Agronomic Traits at Seedling and Maturity Stages of Wheat under Different Potassium Treatments

Potassium (K) is one of the most important mineral nutrients for wheat. In this study, the effects of low K (LK) treatments and the quantitative trait loci (QTLs) for K, calcium (Ca), and magnesium (Mg) use efficiency traits, both at the seedling and maturity stages of wheat, were investigated. The set of “Tainong 18 × Linmai 6” recombinant inbred lines (RILs) were used to identify the QTLs under different K treatments using hydroponic culture and field trials. The majority of K concentrations and content-related traits at seedling and maturity stages decreased with reduced K supply, but the K use efficiency-related traits increased. In contrast, with reduced K supply, the contents of Ca and Mg increased, while the Ca and Mg use efficiency decreased. A total of 217 QTLs for seedling traits and 89 QTLs for adult traits were detected. Four relatively high-frequency QTLs (RHF-QTLs) and 18 QTL clusters (colocation of QTLs for more than two traits) were detected. Eight clusters were detected for K-, Ca-, and Mg-related traits simultaneously. This means that these traits might be controlled by the same QTL. In addition, we highlight that 4B might be an important chromosome regulating the nutrition of K, Ca, and Mg in wheat. The 4B chromosome and four hot QTL clusters, which located 45 QTLs, might be important potential targets for further investigation.

A RID-like putative cytosine methyltransferase homologue controls sexual development in the fungus Podospora anserina

DNA methyltransferases are ubiquitous enzymes conserved in bacteria, plants and opisthokonta. These enzymes, which methylate cytosines, are involved in numerous biological processes, notably development. In mammals and higher plants, methylation patterns established and maintained by the cytosine DNA methyltransferases (DMTs) are essential to zygotic development. In fungi, some members of an extensively conserved fungal-specific DNA methyltransferase class are both mediators of the Repeat Induced Point mutation (RIP) genome defense system and key players of sexual reproduction. Yet, no DNA methyltransferase activity of these purified RID (RIP deficient) proteins could be detected in vitro. These observations led us to explore how RID-like DNA methyltransferase encoding genes would play a role during sexual development of fungi showing very little genomic DNA methylation, if any. To do so, we used the model ascomycete fungus Podospora anserina. We identified the PaRid gene, encoding a RID-like DNA methyltransferase and constructed knocked-out ΔPaRid defective mutants. Crosses involving P. anserina ΔPaRid mutants are sterile. Our results show that, although gametes are readily formed and fertilization occurs in a ΔPaRid background, sexual development is blocked just before the individualization of the dikaryotic cells leading to meiocytes. Complementation of ΔPaRid mutants with ectopic alleles of PaRid, including GFP-tagged, point-mutated and chimeric alleles, demonstrated that the catalytic motif of the putative PaRid methyltransferase is essential to ensure proper sexual development and that the expression of PaRid is spatially and temporally restricted. A transcriptomic analysis performed on mutant crosses revealed an overlap of the PaRid-controlled genetic network with the well-known mating-types gene developmental pathway common to an important group of fungi, the Pezizomycotina.

Genes that bias Mendelian segregation

Mendel laws of inheritance can be cheated by Meiotic Drive Elements (MDs), complex nuclear genetic loci found in various eukaryotic genomes and distorting segregation in their favor. Here, we identify and characterize in the model fungus Podospora anserina Spok1 and Spok2, two MDs known as Spore Killers. We show that they are related genes with both spore-killing distorter and spore-protecting responder activities carried out by the same allele. These alleles act as autonomous elements, exert their effects independently of their location in the genome and can act as MDs in other fungi. Additionally, Spok1 acts as a resistance factor to Spok2 killing. Genetical data and cytological analysis of Spok1 and Spok2 localization during the killing process suggest a complex mode of action for Spok proteins. Spok1 and Spok2 belong to a multigene family prevalent in the genomes of many ascomycetes. As they have no obvious cellular role, Spok1 and Spok2 Spore Killer genes represent a novel kind of selfish genetic elements prevalent in fungal genome that proliferate through meiotic distortion.

Chromosome segregation during meiosis ensures that paternal and maternal chromosomes are equally transmitted to the progeny. Meiotic Drive Elements (MDs) are known to distort this 1∶1 ratio in many animal, plant, and fungal species by killing the gametes not carrying them. Most of the known MDs are complex genetic loci with separate genes for the killing activity and the resistance to said killing. Here, we report in a model fungus on two genes endowed with MD properties previously unreported. Both genes produce a single polypeptide and confer both killing and resistance. They exert their effect irrespective of their position in the genome. They can cross species barriers and promote bias in segregation in other species. As related genes are frequently observed in fungal genomes, we propose that they are representative of a novel kind of selfish genes that propagate by distorting the Mendel laws of segregation.

Maintaining two mating types: structure of the mating type locus and its role in heterokaryosis in Podospora anserina

Pseudo-homothallism is a reproductive strategy elected by some fungi producing heterokaryotic sexual spores containing genetically different but sexually compatible nuclei. This lifestyle appears as a compromise between true homothallism (self-fertility with predominant inbreeding) and complete heterothallism (with exclusive outcrossing). However, pseudohomothallic species face the problem of maintaining heterokaryotic mycelia to fully benefit from this lifestyle, as homokaryons are self-sterile. Here, we report on the structure of chromosome 1 in mat+ and mat- isolates of strain S of the pseudohomothallic fungus Podospora anserina. Chromosome 1 contains either one of the mat+ and mat- mating types of P. anserina, which is mostly found in nature as a mat+/mat- heterokaryotic mycelium harboring sexually compatible nuclei. We identified a "mat" region ∼0.8 Mb long, devoid of meiotic recombination and containing the mating-type idiomorphs, which is a candidate to be involved in the maintenance of the heterokaryotic state, since the S mat+ and S mat- strains have different physiology that may enable hybrid-vigor-like phenomena in the heterokaryons. The mat region contains 229 coding sequences. A total of 687 polymorphisms were detected between the S mat+ and S mat- chromosomes. Importantly, the mat region is colinear between both chromosomes, which calls for an original mechanism of recombination inhibition. Microarray analyses revealed that 10% of the P. anserina genes have different transcriptional profiles in S mat+ and S mat-, in line with their different phenotypes. Finally, we show that the heterokaryotic state is faithfully maintained during mycelium growth of P. anserina, yet mat+/mat+ and mat-/mat- heterokaryons are as stable as mat+/mat- ones, evidencing a maintenance of heterokaryosis that does not rely on fitness-enhancing complementation between the S mat+ and S mat- strains.