Higher reproductive success for chimeras than solitary individuals in the kelp <Emphasis Type="Italic">Lessonia spicata</Emphasis> but no benefit for individual genotypes

Chimerism is a peculiar, yet widespread, type of group living in which genetically heterogeneous entities are created through fusion between conspecifics. Here we tested whether chimerism provides direct benefits to the kelp Lessonia spicata, by analyzing its consequences on reproductive investment and success, at both the genotype and thallus levels. In addition, we quantified the frequency of chimerism in two natural populations, tested if group members were close kin, and evaluated the effects of relatedness and the number of genotypes per thallus on reproduction. Chimeric thalli were frequent (>60 %) in natural populations of L. spicata. In most cases, average intragroup relatedness was not significantly different from the background population. Reproductive investment was not significantly affected by the type of thallus (chimeric versus non-chimeric), by the number of genotypes per thallus or the average relatedness within thallus. Chimerism did not result in net benefits or costs in terms of genotypic reproductive success or probability of reproducing at the genotypic level. Yet, at the thallus level, chimerism increased reproductive success and the probability of reproducing, since more than one genotype reproduced in chimeric thallus. At the population level, chimerism affects L. spicata reproductive success by allowing the coexistence of a higher density of potential reproducers and mates compared to a scenario with only non-chimeric thallus. Chimerism may then have an important effect on the effective population size and possibly in reducing selfing rates.     

Masc2, a gene from Ascobolus encoding a protein with a DNA-methyltransferase activity in vitro, is dispensable for in vivo methylation

We have shown previously that masc1 , a gene encoding a putative C5-DNA-methyltransferase (MTase), was necessary for the de novo 'Methylation Induced Premeiotically' (MIP) process and sexual reproduction in Ascobolus , whereas it was dispensable for maintenance methylation. A second MTase gene from Ascobolus , masc2 , encodes a protein, Masc2, which possesses the large amino-terminal part characteristic of eukaryotic maintenance MTases. In vitro assays have shown that Masc2 displays a methylation activity, suggesting that it might be the MTase responsible for maintenance methylation. To check its function in vivo , we engineered a disruption of the masc2 gene. The resulting mutant strains did not exhibit any particular phenotype during either vegetative growth or sexual reproduction. Neither the masc2 mutation nor the double masc1 masc2 mutation had any detectable effect upon the maintenance of the pre-existing methylation of single gene copies previously subjected to MIP, natural retroelement-like repeats and tandemly repeated rDNA. The masc2 mutation did not alter either MIP or the other de novo methylation process that operates in vegetative cells. Nor did it impair the meiotic process of methylation transfer. These results suggest that at least a third MTase gene responsible for maintenance and vegetative de novo methylation is present in Ascobolus .     

Activities of de-N-glycosylation are ubiquitously found in tomato plant

Activities of two de-N-glycosylation enzymes, PNGase (peptide N ⁴(N-acetyl-glucosaminyl)asparagine amidase) and ENGase (endo N-acetyl-β-D-glucosaminidase), involved in the release of N-glycans from N-glycoproteins, were monitored in several organs of tomato plants (Lycopersicon esculentum, Mill., cv. Dombito) with a fluorescence-HPLC procedure using a resofurin-labelled N-glycopeptide substrate. PNGase and ENGase activities were detected in every organ assayed but with quantitative differences. The highest activities were found in the youngest parts of the plant, i.e. apical buds, flowers and leaf blades. PNGase activities were consistently higher than ENGase activities (three-fold in average). Both de-N-glycosylation activities were associated with high levels of proteins and protease activities. During fruit growth and ripening, these three parameters decreased notably. The ubiquitous detection of these enzyme activities in the different organs is probably associated with the previously characterized unconjugated N-glycans in tomato. The possible role of PNGase and ENGase degradation products (i.e. unconjugated N-glycans) are discussed in relation with their biological functions in plant development.     

Development and characterization of nine polymorphic microsatellite markers in the Chilean kelp Lessonia nigrescens

A total of nine microsatellite loci were isolated and characterized in the Chilean kelp Lessonia nigrescens Bory. Using two different enriched libraries, we observed 1-14 alleles per locus in two samples of 21 kelp individuals each. The observed heterozygosities ranged from 0.05 to 0.80 and all loci are in Hardy-Weinberg equilibrium for one or both samples. Seventeen samples collected from different sites showed high allele diversity along the species distribution. The variation detected at these markers is currently being used for the study of populations of Lessonia nigrescens at different geographical scales.     

DEFENSE EVOLUTION IN THE GRACILARIACEAE (RHODOPHYTA): SUBSTRATE‐REGULATED OXIDATION OF AGAR OLIGOSACCHARIDES IS MORE ANCIENT THAN THE OLIGOAGAR‐ACTIVATED OXIDATIVE BURST1

Combined phylogenetic, physiological, and biochemical approaches revealed that differences in defense‐related responses among 17 species belonging to the Gracilariaceae were consistent with their evolutionary history. An oxidative burst response resulting from activation of NADPH oxidase was always observed in two of the subgenera of Gracilaria sensu lato (Gracilaria, Hydropuntia), but not in Gracilariopsis and in species related to Gracilaria chilensis (“chilensis” clade). On the other hand, all species examined except Gracilaria tenuistipitata var. liui and Gracilariopsis longissima responded with up‐regulation of agar oligosaccharide oxidase to an challenge with agar oligosaccharides. As indicated by pharmacological experiments conducted with Gracilaria chilensis and Gracilaria sp. “dura,” the up‐regulation of agar oligosaccharide oxidase involved an NAD(P)H‐dependent signaling pathway, but not kinase activity. By contrast, the activation of NADPH oxidase requires protein phosphorylation. Both responses are therefore independent, and the agar oligosaccharide‐activated oxidative burst evolved after the capacity to oxidize agar oligosaccharide, probably providing additional defensive capacity to the most recently differentiated clades of Gracilariaceae. As demonstrated with Gracilaria gracilis, Gracilaria dura, and Gracilariopsis longissima, the different responses to agar oligosaccharides allow for a fast and nondestructive distinction among different clades of gracilarioids that are morphologically convergent. Based upon sequences of the chloroplast‐encoded rbcL gene, this study suggests that at least some of the samples from NW America recorded as Gs. lemanaeiformis are probably Gs. chorda. Moreover, previous records of Gracilaria conferta from Israel are shown to be based upon misidentification of Gracilaria sp. “dura,” a species that belongs to the Hydropuntia subgenus.     

GENETIC VARIATION IN WILD AND CULTIVATED POPULATIONS OF THE HAPLOID– DIPLOID RED ALGA GRACILARIA CHILENSIS: HOW FARMING PRACTICES FAVOR ASEXUAL REPRODUCTION AND HETEROZYGOSITY

The extent of changes in genetic diversity and life-history traits associated with farming was investigated in the haploid–diploid red alga, Gracilaria chilensis , cultivated in Chile. This alga belongs to one of the most frequently cultivated seaweed genera around the world. Fifteen farmed populations, 11 wild populations, and two subspontaneous populations were sampled along the Chilean coast. The frequency of reproductive versus vegetative individuals and of haploid versus diploid individuals was checked in each population. In addition, the distribution of genetic variation in wild and cultivated populations was analyzed using six microsatellite markers. Our results first demonstrated that farmed populations are maintained almost exclusively by vegetative propagation. Moreover, the predominance of diploid individuals in farms showed that farming practices had significantly modified life-history traits as compared to wild populations. Second, the expected reduction in genetic diversity due to a cultivation bottleneck and subsequent clonal propagation was detected in farms. Finally, our study suggested that cultural practices in the southern part of the country contributed to the spread of selected genotypes at a local scale. Altogether, these results document for the first time that involuntary selection could operate during the first step of domestication in a marine plant.     

Response of cultured tomato cells subjected to excess zinc: role of cell wall in zinc compartmentation

The aim of this preliminary study was to evaluate the role of the cell wall in Zn accumulation and tolerance by tomato suspension-cultured cells. Growth parameters, Zn distribution and accumulation by tomato cells were determined in function of zinc concentration. A particular attention was paid to the variations of the total cell wall material (cell wall carbohydrates, proteins, and exopolymers) in relation to extracellular levels of Zn. Cells treated with 0.5–5 mM Zn showed typical symptoms of heavy metal toxicity as testified by various growth parameters. Fresh and dry weights as well as total cell volume per vial decreased with increasing Zn concentration in the culture medium. Concurrently, the cell wall biomass increased, as well as the Zn amount retained by cell wall polymers. Cell wall appeared to assume important roles in Zn fixation and could therefore limit Zn influx into the cell. Our results also suggested that zinc fixation by cell wall was not only due to an increase in cell wall biomass but also to an improvement of its binding capacity.