Uniparental mitochondrial DNA inheritance is not affected in Ustilago maydis Δatg11 mutants blocked in mitophagy

Background

Maternal or uniparental inheritance (UPI) of mitochondria is generally observed in sexual eukaryotes, however, the underlying mechanisms are diverse and largely unknown. Recently, based on the use of mutants blocked in autophagy, it has been demonstrated that autophagy is required for strict maternal inheritance in the nematode Caenorhabditis elegans. Uniparental mitochondrial DNA (mtDNA) inheritance has been well documented for numerous fungal species, and in particular, has been shown to be genetically governed by the mating-type loci in the isogamous species Cryptococcus neoformans, Phycomyces blakesleeanus and Ustilago maydis. Previously, we have shown that the a2 mating-type locus gene lga2 is decisive for UPI during sexual development of U. maydis. In axenic culture, conditional overexpression of lga2 triggers efficient loss of mtDNA as well as mitophagy. To assess a functional relationship, we have investigated UPI in U. maydis Δatg11 mutants, which are blocked in mitophagy.

Results

This study has revealed that Δatg11 mutants are not affected in pathogenic development and this has allowed us to analyse UPI under comparable developmental conditions between mating-compatible wild-type and mutant strain combinations. Explicitly, we have examined two independent strain combinations that gave rise to different efficiencies of UPI. We demonstrate that in both cases UPI is atg11-independent, providing evidence that mitophagy is not critical for UPI in U. maydis, even under conditions of strict UPI.

Conclusions

Until now, analysis of a role of mitophagy in UPI has not been reported for microbial species. Our study suggests that selective autophagy does not contribute to UPI in U. maydis, but is rather a consequence of selective mtDNA elimination in response to mitochondrial damage.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-015-0358-z) contains supplementary material, which is available to authorized users.     

Gene Action of Dollar Spot Resistance in Creeping Bentgrass

The dollar spot disease, incited by Sclerotinia homoeocarpa F.T. Bennet, is one of the most important diseases of creeping bentgrass (Agrostis stolonifera L.) on golf courses. An understanding of the inheritance of dollar spot resistance could enhance genetic improvement efforts in creeping bentgrass. The objectives of this study were to evaluate the response of two creeping bentgrass crosses to two different isolates of S. homoeocarpa, determine gene action and identify number of loci involved in resistance to individual fungal isolates. Parental clones, pseudo F₂, pseudo F₃, BC₁ and BC₂ progenies from two crosses were established in a field trial in a randomized complete block split‐plot design in the fall of 2002. Progeny of each generation (subplots) were inoculated with each of two isolates of S. homoeocarpa (main plots) applied at a rate of 0.25 g/m² of prepared inoculum and evaluated for dollar spot disease. Minimum loci calculations averaged 1.0–2.6. Midparent heterosis calculations were not significant. Backcross population means were closest to the recurrent parent. Generation mean analysis supports a simple additive‐dominance model for both crosses and both isolates, although there was also some evidence of epistatic gene action depending on the cross and the isolate. These results confirm previous research that dollar spot disease is quantitatively inherited and indicate that there may be a few genes interacting in a mainly additive fashion to confer dollar spot disease resistance in creeping bentgrass.     

Property and wealth inequality as cultural niche construction

In contrast to other approaches, evolutionary perspectives on understanding the power and wealth inequalities in human societies view wealth and power not as ends in themselves but as proximate goals that contribute to the ultimate Darwinian goal of achieving reproductive success. The most successful means of achieving it in specific times and places depend on local conditions and these have changed in the course of human history, to such an extent that strategies focused on the maintenance and increase of wealth can even be more successful in reproductive terms than strategies directed at maximizing reproductive success in the short term. This paper argues that a major factor leading to such changes is a shift in the nature of inter-generational wealth transfers from relatively intangible to material property resources and the opportunities these provided for massively increased inequality. This shift can be seen as a process of niche construction related to the increasing importance of fixed and defensible resources in many societies after the end of the last Ice Age. It is suggested that, despite problems of inference, the evidence of the archaeological record can be used to throw light on these processes in specific places and times.     

HYBRIDOGENESIS AND ANDROGENESIS IN THE STICK-INSECT BACILLUS ROSSIUS-GRANDII BENAZZII (INSECTA,PHASMATODEA)

In northwestern Sicily interspecific hybrid females between Bacillus rossius and B. grandii benazzii (Insecta, Phasmatodea) are sympatric with facultatively parthenogenetic demes of the former and bisexual populations of the latter. Preliminary observations suggested that hybrid females are maintained by hybridogenetic reproduction, not by current F₁ hybrid production nor through parthenogenesis. Being hybridogens, a complex of hemiclonal lineages, we informally refer to them as B. rossius-grandii benazzii, according to Schultz's proposal. In this study B. rossius-g. benazzii females were crossed with males of B. g. benazzii, B. g. grandii, B. g. maretimi, and B. rossius. Allozyme analysis of the progeny showed that the great majority of them were actually produced by hybridogenesis with a hemiclonal inheritance of the maternal B. rossius genotype (Br^m) and actual syngamy with a sperm from the fathering male, so that Br^m-gb^p, Br^m-gg^p, Br^m-gm^p, and Br^m-r^p offspring were obtained in the respective crosses. All-paternal progeny (androgenetics) were also produced (Bgb^pgb^p, Bgm^pgm^p, Br^pr^p) and two gynogenetic descendants were observed. Cytological investigations on virgin eggs that failed to hatch revealed in most of them a haploid-diploid blocked blastoderm; this rudimentary parthenogenesis appears to be an important prerequisite for further evolution of this hybridogen. Reproductive modes of descendants were also analyzed; although Br^m-g^p hybrids are still able to reproduce by hybridogenesis, a progressive disruption of the hybridogenetic-androgenetic system takes place in synthetic B. rossius (Br^m-r^p, Br^pr^p) and abundant thelytokous parthenogenetic offspring are obtained from females of androgenetic origin. The evolutionary role of these hybridogens appears to be linked to their shift towards parthenogenesis; this has apparently occurred in the southeastern Sicilian hybrid B. whitei (=B. rossius/g. grandii), which exhibits both hybridogenesis and parthenogenesis.     

Influence of metabolic stress on the inheritance of cell determination in the moss, Pottia intermedia

Epigenetically-determined apogamy in aposporous regenerants of the moss Pottia intermedia persists during vegetative propagation, the capacity of apogamy being inherited by individual aposporous protonemal cells. To test Bauer-Lazarenko's proposal that stable apogamy in mosses may be due to some self-replicating cytoplasmic factor, the effects of different metabolic stress treatments on the expression of apogamy have been tested. Chronic metabolic stress caused by long-term growth of autotrophic aposporous protonema on mineral medium with 0.25% of casamino acids and on Murashiga-Skoog (MS) medium with sucrose and phytohormones, as well as by transitory action of high kinetin concentration, have a much stronger influence on the expression of apogamy, than short-term stress treatments with RNase and Pb(2+). Apogamy has been found to be lost stably, after prolonged growth on MS medium containing kinetin and ABA. The proposal that the capacity for apogamy is related to the release of aposporous protonemal cells from a putative factor for apogamy is discussed.     

Aster self-organization at meiosis: a conserved mechanism in insect parthenogenesis?

Unfertilized eggs usually lack maternal centrosomes and cannot develop without sperm contribution. However, several insect species lay eggs that develop to adulthood as unfertilized in the absence of a preexisting centrosome. We report that the oocyte of the parthenogenetic viviparous pea aphid Acyrthosiphon pisum is able to self-organize microtubule-based asters, which in turn interact with the female chromatin to form the first mitotic spindle. This mode of reproduction provides a good system to investigate how the oocyte can assemble new centrosomes and how their number can be exactly monitored. We propose that the cooperative interaction of motor proteins and randomly nucleated surface microtubules could lead to the formation of aster-like structures in the absence of pre-existing centrosomes. Recruitment of material along the microtubules might contribute to the accumulation of pericentriolar material and centriole precursors at the focus of the asters, thus leading to the formation of true centrosomes. The appearance of microtubule asters at the surface of activated oocytes could represent a possible common mechanism for centrosome formation during insect parthenogenesis.     

Genetic analysis of diet-induced hypercholesterolemia in exogenously hypercholesterolemic rats

The exogenously hypercholesterolemic (ExHC) rat is an established strain that exhibits a polygenic syndrome of hypercholesterolemia after feeding on a cholesterol-containing diet, and the extent of this differs between male and female rats in the strain. The present study was performed to determine the genetic background of diet-induced hypercholesterolemia in ExHC rats. We used quantitative trait locus (QTL) analyses of the F2 progeny derived from ExHC and Brown-Norway rats. Rats were fed a diet containing 1% cholesterol, and a genome-wide scan was then performed. Significant QTLs for serum total cholesterol levels were revealed on chromosomes 5 and 14 in the vicinity of markers D5Rat95 and D14Rat43, having maximum logarithm of the odds scores of 6.0 and 5.8, respectively. A suggestive QTL for the trait was also detected on chromosome 3 at D3Rat140. In particular, the QTL on chromosome 5 was specific for female rats. These loci were novel QTLs for post-dietary serum total cholesterol levels. In addition, cross-mating analysis in F1 generations suggested that the responsiveness to dietary cholesterol in ExHC rats is partly attributable to X-linked inheritance. Identifying such genetic factors may be useful in predicting the risks associated with diet-induced hypercholesterolemia in humans.     

Genetic and environmental interactions determine seizure susceptibility in epileptic EL mice

Gene identification has progressed rapidly for monogenic epilepsies, but complex gene-environmental interactions have hindered progress in gene identification for multifactorial epilepsies. We analyzed the role of environmental risk factors in the inheritance of multifactorial idiopathic generalized epilepsy in the EL mouse. Seizure susceptibility was evaluated in the EL (E) and seizure-resistant ABP/LeJ (A) parental mouse strains and in their AEF1 and AEF2 hybrid offspring using a handling-induced seizure test. The seizure test was administered in three environments (environments I, II and III) that differed with respect to the number of seizure tests administered (one test or four tests) and the age of the mice when tested (young or old). The inheritance of seizure susceptibility appeared dominant after repetitive seizure testing in young or old mice, but recessive after a single test in old mice. Heritability was high (0.67-0.77) in each environment. Significant quantitative trait loci (QTL) that were associated with environments I and III (repetitive testing) were found on chromosomes 2 and 9 and colocalized with previously mapped El2 and El4, respectively. The El2 QTL found in environment I associated only with female susceptibility. A novel QTL, El-N, for age-dependent predisposition to seizures was found on proximal chromosome 9 only in environment II. The findings indicate that environmental risk factors determine the genetic architecture of seizure susceptibility in EL mice and suggest that QTL for complex epilepsies should be defined in terms of the environment in which they are expressed.     

Segregation Analysis on Genetic System of Quantitative Traits in Plants

Based on the traditional polygene inheritance model of quantitative traits,the author suggests the major gene and polygene mixed inheritance model.The model was considered as a general one,while the pure major gene and pure polygene inheritance model was a specific case of the general model.Based on the proposed theory,the author established the segregation analysis procedure to study the genetic system of quantitative traits of plants.At present,this procedure can be used to evaluate the genetic effect of individual major genes (up to two to three major genes),the collective genetic effect of polygene,and their heritability value.This paper introduces how to establish the procedure,its main achievements,and its applications.An example is given to illustrate the steps,methods,and effectiveness of the procedure.