Two linear plasmids in mitochondria of Fusarium solani f. sp. cucurbitae

Two linear plasmid-like DNAs designated pFSC1 (9.2 kbp) and pFSC2 (8.3 kbp) were found in an isolate of the plant pathogenic fungus Fusarium solani f. sp. cucurbitae race 1. The plasmids were maternally inherited and copurified with mitochondrial DNA obtained from a mitochondria-enriched cell fraction suggesting that they are located in mitochondria. The plasmids did not share extensive sequence similarity. No homology was detected between either plasmid and the nuclear or mitochondrial genome when cloned plasmids were used as probes in Southern hybridization analyses. The fungus was cured of plasmids by ethidium bromide treatment. Compared to the plasmid-containing isolate, plasmid-cured derivatives had reduced pathogenicity on a susceptible plant host, Cucurbita maxima "Pink Banana."     

Morphology of the fifth sternal glands of Neotropical social wasps (Hymenoptera,Vespidae, Polistinae)

Glands play a central role in the social behavior of insects, and comparative analysis of their structure may provide insights about their evolution and their role in insect social biology. Here, we describe the glands of the fifth metasomal sternite of ten polistine wasps with different social behaviors. The glands of foragers of these species were studied using semithin sections of Araldite‐embedded tissue, and scanning electron microscopy. The structure of the glands observed was mostly similar to what has previously been reported for independent‐founder and swarm‐founder species, respectively. Scale‐shaped modifications in the fifth sternite are reported for the first time for members of the genera Synoeca and Epipona. Two previously unreported glands in the fifth sternite are also described. A more restrictive definition of the name Richards' gland is proposed, applying to the class 3 cells associated with scale modifications of the fifth sternite, based on structural differences between the glands observed, homology requirements, and functional evidence. Previous phylogenetic reconstructions of this character suggest that it appeared early in the Vespidae and disappeared four times, with a single reappearance in the genus Vespula. The restricted definition of Richards' gland suggests that this structure is an exclusive trait of the Epiponini, with two reversals.     

Spatial variation in frequency and intensity of antibiotic interactions among Streptomycetes from prairie soil

Antibiotic interactions are believed to be significant to microbial fitness in soil, yet little is known of the frequency, intensity, and diversity of antibiotic inhibition and resistance among indigenous microbes. To begin to address these issues, we studied the abilities of streptomycete isolates from prairie soil to inhibit growth and display resistance to antibiotics produced by a test collection of 10 streptomycete isolates. Wide variations in antibiotic inhibition and resistance for prairie isolates among three locations and four soil depths within a 1-m2 plot were revealed. Fewer than 10% of 153 prairie isolates inhibited all 10 test isolates, while more than 40% of the isolates did not inhibit any of the test isolates. No field isolate was resistant to all of the test isolates, nor was any isolate susceptible to all of the test isolates. No correlation between inhibition and resistance phenotypes was found, suggesting that inhibition and resistance are under independent selection. The significant spatial variation in the frequency and intensity of antibiotic inhibition implies that the fitness benefits of antibiotic production are not the same among locations in soil. In contrast, the consistency of resistance over space indicates that its significance to fitness across locations is stable or the costs of maintaining resistance in the absence of selection are small or nonexistent. The spatial clustering of antibiotic inhibitory activity suggests a variable matrix of selection pressures and microbial responses across the soil landscape.     

Aluminum resistance mechanisms in oat (Avena sativa L.)

Background and aims

Enhanced aluminum (Al) resistance has been observed in dicots over-expressing enzymes involved in organic acid synthesis; however, this approach for improving Al resistance has not been investigated in monocots. Among the cereals, oat (Avena sativa L.) is considered to be Al resistant, but the basis of resistance is not known.

Methods

A hydroponic assay and hematoxylin staining for Al accumulation in roots were used to evaluate Al resistance in 15 oat cultivars. Malate and citrate release from roots was measured over a 24?h period. A malate dehydrogenase gene, neMDH, from alfalfa (Medicago sativa L.) was used to transform oat.

Results

Oat seedlings were highly resistant to Al, as a concentration of 325?μM AlK(SO₄)₂ was needed to cause a 50% decrease in root growth. Most oat cultivars tested are naturally resistant to high concentrations of Al and effectively excluded Al from roots. Al-dependent release of malate and Al-independent release of citrate was observed. Al resistance was enhanced in a transgenic oat line with the highest accumulation of neMDH protein. However, overall root growth of this line was reduced and expression of neMDH in transgenic oat did not enhance malate secretion.

Conclusions

Release of malate from oat roots was associated with Al resistance, which suggests that malate plays a role in Al resistance of oat. Over-expression of alfalfa neMDH enhanced Al resistance in some lines but was not effective alone for crop improvement.     

Suppression of the root-lesion nematode (Pratylenchus penetrans) in alfalfa (Medicago sativa) by Streptomyces spp.

Strains of Streptomyces were tested for their ability to reduce population densities of the root-lesion nematode (RLN), Pratylenchus penetrans, in roots of alfalfa (Medicago sativa) in growth chamber assays. Previously, these strains were shown to suppress potato scab disease, caused by Streptomyces scabies, in field experiments and to inhibit in vitrogrowth of a wide range of plant-pathogenic fungi and bacteria. Inoculation with Streptomyces at planting significantly reduced RLN population densities in roots of both susceptible and resistant alfalfa varieties grown in either heat-treated or untreated soil. Reductions in RLN population densities were observed 6 weeks after nematode inoculation. Shoot dry matter was not affected by any treatment; root dry weight was reduced in Streptomycesplus nematode treatments compared to the nematode inoculation alone in some experiments but was not affected by Streptomyces when RLN was absent. Mutant strains not producing antibiotics in vitro also reduced RLN population densities in alfalfa roots and all strains maintained high population densities after inoculation into heat-treated soil and on alfalfa roots. These strains may be useful in multi-crop, multi-pathogen management programs to augment genetic resistance to plant diseases.     

The alfalfa (Medicago sativa) TDY1 gene encodes a mitogen-activated protein kinase homolog.

Development of root nodules, specifically induction of cortical cell division for nodule initiation, requires expression of specific genes in the host and microsymbiont. A full-length cDNA clone and the corresponding genomic clone encoding a MAP (mitogen-activated protein) kinase homolog were isolated from alfalfa (Medicago sativa). The genomic clone, TDY1, encodes a 68.9-kDa protein with 47.7% identity to MMK4, a previously characterized MAP kinase homolog from alfalfa. TDY1 is unique among the known plant MAP kinases, primarily due to a 230 amino acid C-terminal domain. The putative activation motif, Thr-Asp-Tyr (TDY), also differs from the previously reported Thr-Glu-Tyr (TEY) motif in plant MAP kinases. TDY1 messages were found predominantly in root nodules, roots, and root tips. Transgenic alfalfa and Medicago truncatula containing a chimeric gene consisting of 1.8 kbp of 5' flanking sequence of the TDY1 gene fused to the beta-glucuronidase (GUS) coding sequence exhibited GUS expression primarily in the nodule parenchyma, meristem, and vascular bundles, root tips, and root vascular bundles. Stem internodes stained intensely in cortical parenchyma, cambial cells, and primary xylem. GUS activity was observed in leaf mesophyll surrounding areas of mechanical wounding and pathogen invasion. The promoter was also active in root tips and apical meristems of transgenic tobacco. Expression patterns suggest a possible role for TDY1 in initiation and development of nodules and roots, and in localized responses to wounding.