A single amino acid substitution in highly similar endo-PGs from Fusarium verticillioides and related Fusarium species affects PGIP inhibition

Endo-polygalacturonase (PG) may be a critical virulence factor secreted by several fungi upon plant invasion. The single-copy gene encoding PG in Fusarium verticillioides and in eight other species of the Gibberella fujikuroi complex (F. sacchari, F. fujikuroi, F. proliferatum, F. subglutinans, F. thapsinum, F. nygamai, F. circinatum, and F. anthophilum) was functionally analyzed in this paper. Both the nucleotide and amino acid sequences were highly similar among the 12 strains of F. verticillioides analyzed, as well as among those from the G. fujikuroi complex. The PGs were not inhibited by the polygalacturonase-inhibiting proteins (PGIPs) from the monocot asparagus and leek plants, but were inhibited to variable extents by bean PGIP. PGs from F. verticillioides, F. nygamai and one strain of F. proliferatum were barely inhibited. Residue 97 within PG was demonstrated to contribute to the different levels of inhibition. Together these findings provide new insights into the structural and functional relationships between the PG from the species of the G. fujikuroi complex and the plant PGIP.     

A measure of sexual selection in hermaphroditic animals: parentage skew and the opportunity for selection

The role of sexual selection in shaping the mating system of hermaphrodites is currently widely accepted. However, a quantification of the intensity of sexual selection in hermaphroditic animals has never been accomplished. We evaluated the opportunity for sexual selection for both the female and the male functions in the simultaneous outcrossing hermaphrodite Ophryotrocha diadema by measuring focal hermaphrodites' paternal and maternal offspring in experimental replicated monogamous and promiscuous populations, using genetic markers to estimate paternity. Opportunity for sexual selection for each of the two sexual functions was quantified by means of the Crow's index, i.e. the ratio of variance in progeny number to the squared mean number of progeny. In addition, the extent to which the reproductive success was shared among competing individuals was estimated by means of the Nonacs's B index. We documented that the strength of selection on the male and female function in hermaphrodites with external fertilization depends on the reproductive context. Under a promiscuous regime, hermaphrodites have higher opportunities for selection for both the male and the female function than under the monogamous regime. Moreover, the reproductive skew for the female function becomes greater than that for the male function, moving from monogamy to promiscuity. In our model system, allocation to one sexual function is opposed by any degree of allocation to the other, indicating that sex-specific patterns of selection operate in this model species.     

Inherited and somatic cytogenetic variability in Palearctic populations of Chironomus riparius Meigen 1804 (Diptera, Chironomidae).

Inter- and intracytogenetic variability was analyzed in 13 natural Palearctic populations of Chironomus riparius Meigen 1804 (syn. Chironomus thummi) by examining hereditary and somatic aberrations (mainly inversions) of the salivary gland polytene chromosomes. In total, 77 different types of inherited inversion sequences and 184 different types of somatic inversions were found. The median percent frequency of inherited inversions was 1.4% and karyotypic divergence between populations was very low. Most hereditary inversions were endemic and always in a heterozygous state. Only six inversion sequences, each of them shared by two very distant populations, may be considered a relic of very ancient ancestral inversions. Unlike inherited inversions, occurrence of somatic aberrations seems to increase with the overall rise in the level of heavy metal pollution of the sediments from which larvae were sampled. In contrast with what occurs in populations of other chironomid species, populations of C. riparius do not seem to undergo a process of cytogenetic differentiation.     

Nonrandom chromosomal distribution of spontaneous breakpoints and satellite DNA clusters in two geographically distant populations of Chironomus riparius (Diptera: Chironomidae)

Two geographically distant populations of Chironomus riparius (syn. C. thummi) from two environmentally polluted sites (Santena, Italy and Varna, Bulgaria) show numerous somatic and inherited chromosomal aberrations (inversions, deletions and deficiencies). Fifty-five percent of the observed breakpoints occurred in at least two larvae from both populations. Breakpoints occurring twice or more were considered as common structural chromosomal breakpoints. We tested whether such common breakpoints in larvae of the two polluted populations had a random chromosomal distribution or occurred preferentially in specific heterochromatic regions. Distribution of common breakpoints was not random, and proximal regions of first and third chromosome had significantly more common breakpoints than distal ones. By FISH we identified and mapped 56 chromosomal sections containing clusters of two tandem-repetitive satellite DNA families called Hinf and Alu elements. Like the common breakpoints, these repetitive DNA clusters appeared to be significantly more abundant in regions of constitutive heterochromatin such as the pericentromeric regions, while in distal sections of chromosomal arms they were rare or absent. Twenty-four out of 45 common breakpoints (i.e., 53.3%) occurred in cytogenetic sections where Alu and Hinf satellite DNA probes hybridized. The frequency of co-localization between common breakpoints and repetitive DNA hybridization signals was significantly higher than expected by chance. We hypothesize that spontaneous or induced breaks occur more frequently in sections containing blocks of repetitive DNA.     

Effect of Environmental Pollution on the Chromosomal Variability of Chironomus Riparius

Different frequencies of chromosomal alterations in salivary gland polytene chromosomes AB, CD and EF were described in larvae of Chironomus riparius (syn. Chironomus thummi) from the trace metal-polluted station of Santena on the river Banna, near Turin, and from the unpolluted station of Corio (40 Km from Turin) which was taken as a reference area. In a sample of 56 larvae from Santena, no specimen with the standard karyotype in all cells of the salivary glands was found. Different types of aberrations were found: 33 paracentric and five pericentric inversions, three deficiencies, four amplified sections and one chromatid break. Fifteen out of the 38 inversions and two amplified sections appeared to be inherited, while all the other aberrations were somatic. Most of the aberrations' breakpoints were located on both sides of the centromere regions, where constitutive heterochromatin is present. Also functional alterations were observed (mainly telomere and centromere decondensations and nine novel puffs). In a sample of 49 larvae of a population from the well-preserved area of Corio only six somatic and one inherited paracentric inversions were found. These results suggest that the strong destabilization of the genomes of C. riparius larvae from Santena could be a reaction to the activity of the toxic substances present in the polluted sediments of the river Banna. This revised version was published online in August 2006 with corrections to the Cover Date.     

The xylanase inhibitor TAXI‐III counteracts the necrotic activity of a Fusarium graminearum xylanase in vitro and in durum wheat transgenic plants

The xylanase inhibitor TAXI‐III has been proven to delay Fusarium head blight (FHB) symptoms caused by Fusarium graminearum in transgenic durum wheat plants. To elucidate the molecular mechanism underlying the capacity of the TAXI‐III transgenic plants to limit FHB symptoms, we treated wheat tissues with the xylanase FGSG_03624, hitherto shown to induce cell death and hydrogen peroxide accumulation. Experiments performed on lemmas of flowering wheat spikes and wheat cell suspension cultures demonstrated that pre‐incubation of xylanase FGSG_03624 with TAXI‐III significantly decreased cell death. Most interestingly, a reduced cell death relative to control non‐transgenic plants was also obtained by treating, with the same xylanase, lemmas of TAXI‐III transgenic plants. Molecular modelling studies predicted an interaction between the TAXI‐III residue H395 and residues E122 and E214 belonging to the active site of xylanase FGSG_03624. These results provide, for the first time, clear indications in vitro and in planta that a xylanase inhibitor can prevent the necrotic activity of a xylanase, and suggest that the reduced FHB symptoms on transgenic TAXI‐III plants may be a result not only of the direct inhibition of xylanase activity secreted by the pathogen, but also of the capacity of TAXI‐III to avoid host cell death.     

Glycerol-based sterilization bioindicator system from Bacillus atrophaeus: development, performance evaluation, and cost analysis

The development of new value-added applications for glycerol is of worldwide interest because of the environmental and economic problems that may be caused by an excess of glycerol generated from biodiesel production. A novel use of glycerol as a major substrate for production of a low-cost sterilization biological indicator system (BIS; spores on a carrier plus a recovery medium) was investigated. A sequential experimental design strategy was applied for product development and optimization. The proposed recovery medium enables germination and outgrowth of heat-damaged spores, promoting a D _160 °C value of 6.6?±?0.1 min. Bacillus atrophaeus spores production by solid-state fermentation reached a 2.3?±?1.2?×?10⁸?CFU/g dry matter. Sporulation kinetics results allowed this process to be restricted in 48 h. Germination kinetics demonstrated the visual identification of nonsterile BIS within 24 h. Performance evaluation of the proposed BIS against dry-heat and ethylene oxide sterilization showed compliance with the regulatory requirements. Cost breakdowns were from 41.8 (quality control) up to 72.8 % (feedstock). This is the first report on sterilization BIS production that uses glycerol as a sole carbon source, with significant cost reduction and the profitable use of a biodiesel byproduct.