Investigation of yeast genes possibly involved in mtDNA stability using the nematode Caenorhabditis elegans

Screening of Caenorhabditis elegans genes possibly involved in the mitochondrial genome maintenance was performed using our previous validated method of RNAi combined with ethidium bromide. This was to knock down C. elegans genes homologous to yeast genes known to be involved in mtDNA stability but of unknown molecular function or to identify transient components that could play important role on the stability of mtDNA in a temporal and/or spatial manner. C. elegans homologs for 11 genes among 27 yeast genes for which deletion leads to a rho0 state were found, however, only 5 genes were present in the RNAi library. Out of these 5 genes, 1 gene (homolog of GEM1) gave a clear L3 arrest on RNAi and ethidium bromide indicating its involvement on mtDNA stability. Four other genes homologs of MTG2, YER087W, AVL9 and RRG3 did not lead to L3 arrest even though their deletion in Saccharomyces cerevisiae leads to rho0 state. Although MTG2 has been reported to be important in the function and structure on mtDNA stability in yeast, our results did not support those findings in C. elegans. The human homolog of this gene (MIRO1) can be considered as a candidate gene involved in mtDNA stability and sequenced in patients with mtDNA depletion diseases.Keywords: mtDNA, Caenorhabditis elegans, nucleoid, RNAi, candidate genes, homolog, MIRO

Dissection of the Carboxyl-Terminal Domain of the Proteasomal Subunit Rpn11 in Maintenance of Mitochondrial Structure and Function

We have previously demonstrated that the C-terminal part of Rpn11, a deubiquitinating enzyme in the lid of the proteasome, is essential for maintaining a correct cell cycle and normal mitochondrial morphology and function. The two roles are apparently unlinked as the mitochondrial role is mapped to the Carboxy-terminus, whereas the catalytic deubiquitinating activity is found within the N-terminal region. The mitochondrial defects are observed in rpn11-m1 (originally termed mpr1-1), a mutation that generates Rpn11 lacking the last 31 amino acids. No mitochondrial phenotypes are recorded for mutations in the MPN/JAMM motif. In the present study, we investigated the participation of the last 31 amino acids of the Rpn11 protein by analysis of intragenic revertants and site-specific mutants. We identified a putative -helix necessary for the maintenance of a correct cell cycle and determined that a very short region at the C-terminus of Rpn11 is essential for the maintenance of tubular mitochondrial morphology. Furthermore, we show that expression of the C-terminal part of Rpn11 is able to complement in trans all of the rpn11-m1 mitochondrial phenotypes. Finally, we investigate the mechanisms by which Rpn11 controls the mitochondrial shape and show that Rpn11 may regulate the mitochondrial fission and tubulation processes

Size and Content of the Sex-Determining Region of the Y Chromosome in Dioecious <i>Mercurialis annua</i>, a Plant with Homomorphic Sex Chromosomes.

Dioecious plants vary in whether their sex chromosomes are heteromorphic or homomorphic, but even homomorphic sex chromosomes may show divergence between homologues in the non-recombining, sex-determining region (SDR). Very little is known about the SDR of these species, which might represent particularly early stages of sex-chromosome evolution. Here, we assess the size and content of the SDR of the diploid dioecious herb &lt;i&gt;Mercurialis annua&lt;/i&gt; , a species with homomorphic sex chromosomes and mild Y-chromosome degeneration. We used RNA sequencing (RNAseq) to identify new Y-linked markers for &lt;i&gt;M. annua.&lt;/i&gt; Twelve of 24 transcripts showing male-specific expression in a previous experiment could be amplified by polymerase chain reaction (PCR) only from males, and are thus likely to be Y-linked. Analysis of genome-capture data from multiple populations of &lt;i&gt;M. annua&lt;/i&gt; pointed to an additional six male-limited (and thus Y-linked) sequences. We used these markers to identify and sequence 17 sex-linked bacterial artificial chromosomes (BACs), which form 11 groups of non-overlapping sequences, covering a total sequence length of about 1.5 Mb. Content analysis of this region suggests that it is enriched for repeats, has low gene density, and contains few candidate sex-determining genes. The BACs map to a subset of the sex-linked region of the genetic map, which we estimate to be at least 14.5 Mb. This is substantially larger than estimates for other dioecious plants with homomorphic sex chromosomes, both in absolute terms and relative to their genome sizes. Our data provide a rare, high-resolution view of the homomorphic Y chromosome of a dioecious plant

A partially sex-reversed giant kelp sheds light into the mechanisms of sexual differentiation in a UV sexual system

In UV sexual systems, sex is determined during the haploid phase of the life cycle and males have a V chromosome whereas females have a U chromosome. Previous work in the brown alga Ectocarpus revealed that the V chromosome has a dominant role in male sex determination and suggested that the female developmental programme may occur by 'default'. Here, we describe the identification of a genetically male giant kelp strain presenting phenotypic features typical of a female, despite lacking the U-specific region. The conversion to the female developmental programme is however incomplete, because gametes of this feminized male are unable to produce the sperm-attracting pheromone lamoxirene. We identify the transcriptomic patterns underlying the male and female specific developmental programmes, and show that the phenotypic feminization is associated with both feminization and de-masculinization of gene expression patterns. Importantly, the feminization phenotype was associated with dramatic downregulation of two V-specific genes including a candidate male-determining gene. Our results reveal the transcriptional changes associated with sexual differentiation in a UV system, and contribute to disentangling the role of sex-linked and autosomal gene expression in the initiation of sex-specific developmental programmes. Overall, the data presented here imply that the U-specific region is not required to initiate the female developmental programme, but is critical to produce fully functional eggs, arguing against the idea that female is the 'default' sex in this species

Enhanced leaky sex expression is an adaptive plastic response to pollen limitation in the dioecious plant<i>Mercurialis annua</i>

AbstractPhenotypic plasticity is almost ubiquitous across the tree of life, but clear demonstrations that it is adaptive are rare. In dioecious plants, males and females frequently show ‘leaky’ sex expression, with individuals occasionally producing flowers of the opposite sex. Here, we demonstrate that leaky sex expression in the wind-pollinated dioecious herbMercurialis annuais plastically responsive to its mating context. We compared experimental populations of females growing either with or without males. Females growing in the absence of males were leakier in their sex expression than controls with males, producing more than twice as many male flowers. Moreover, because greater leakiness was more highly represented in the population’s progeny, we conclude that enhanced leakiness in sex expression is adaptive inM. annua. We discuss differences in the degree of plasticity between ploidal races ofMercurialis annuain terms of likely differences in the reliability of the signal plants may perceive for the presence of males in their populations. Our results provide a striking instance of adaptive plasticity in the reproductive behavior of plants and draw attention to possible constraints on plasticity when the environmental signals that individuals receive are unreliable.</jats:p

total_data_2012-2014_continuum.csv

Sex allocation data of Mercurialis annua experimental populatons grown in 1:1 sex ratio in 2012 and 201

YY males of the dioecious plant<i>Mercurialis annua</i>are fully viable but produce largely infertile pollen

SummaryThe suppression of recombination during sex-chromosome evolution is thought to be favoured by linkage between the sex-determining locus and sexually-antagonistic loci, and leads to the degeneration of the chromosome restricted to the heterogametic sex. Despite substantial evidence for genetic degeneration at the sequence level, the phenotypic effects of the earliest stages of sex-chromosome evolution are poorly known. Here, we compare the morphology, viability and fertility between XY and YY individuals produced by crossing seed-producing males in the dioecious plantMercurialis annuaL., which has young sex chromosomes with limited X-Y sequence divergence. We found no significant difference in viability or vegetative morphology between XY and YY males. However, electron microscopy revealed clear differences in pollen anatomy, and YY males were significantly poorer sires in competition with their XY counterparts. Our study suggests either that the X chromosome is required for full male fertility inM. annua, or that male fertility is sensitive to the dosage of relevant Y-linked genes. We discuss the possibility that the maintenance of male-fertility genes on the X chromosome might have been favoured in recent population expansions, which selected for the ability of females to produce pollen in the absence of males.</jats:p