New capabilities for Mycosphaerella graminicola research

Mycosphaerella graminicola is a major pathogen of wheat worldwide, causing Septoria leaf blotch disease. Targeted gene disruption in M. graminicola, by Agrobacterium tumefaciens‐mediated transformation, has become an established functional genomics tool for M. graminicola research in recent years. However, in order to advance research into this economically important pathogen, further functional genomics tools need to be developed. Here, we report three new capabilities for M. graminicola research: (i) two selectable markers have been shown to work robustly in M. graminicola, namely G418 and the fungicide carboxin; (ii) the generation of a strain of M. graminicola in which the KU70 (MUS‐51) homologue has been disrupted; in this strain, homologous recombination efficiencies increased to more than 95%, whilst maintaining wild‐type growth in vitro and full pathogenicity on wheat leaves; (iii) the ability to efficiently target and generate precise mutations of specific genes in the genomic context in M. graminicola. In addition, the insertion of the E198A mutation into the β‐tubulin gene (MgTUB1), conferring resistance to the fungicide benomyl, suggests that this mutant allele may provide an additional selectable marker. The collective use of these tools will permit further advancements in our knowledge of the biology and pathogenicity of this important plant pathogen.     

Revision and cladistic analysis of the eumenine wasp genus Pseudodynerus de Saussure (Hymenoptera, Vespidae, Eumeninae)

Abstract.  The eumenine genus Pseudodynerus is revised, and the phylogenetic relationships among its species are reconstructed based on adult morphology. The cladistic analyses of the 21 terminal species (15 ingroup and six outgroup species) and 48 characters, from external morphology and male genitalia, produced one cladogram under equal weights and two under implied weights. The monophyly of Pseudodynerus was corroborated in all three hypotheses, although the internal relationships varied depending on the weighting scheme. Two major clades were recovered under both equal and implied weights, one containing mostly Central and North American species and the other only South American species. The main difference between the hypotheses involves the placement of P. luctuosus , which comes out either as sister to a clade formed by P. hallinani  + ( P. maxillaris  +  P. quadrisectus  +  P. crypticus ) or as sister to a clade comprising the remaining species. Fifteen species of Pseudodynerus are recognized, of which four are described as new: P. crypticus from Costa Rica, P. carpenteri from French Guiana and Suriname, P. obesus from Rondônia, Brazil, and P. singularis from Espírito Santo, Brazil. One new synonymy is proposed: Odynerus ( Odynerus ) aztecus de Saussure, 1857  =  Pseudodynerus quadrisectus ( Say, 1837 ) syn.n. Names treated as varieties by Bequaert (1941) are not recognized at any level herein, as follows: Monobia mina-palumboi Gribodo, 1891 , stat.rev. ; Odynerus ( Leionotus ) beelzebub Zavattari, 1912 , stat.rev. ; Stenodynerus anisitsii garleppi Schrottky, 1911 , stat.rev. ; and Stenodynerus mondaiensis Bertoni, 1918, stat.rev. Lectotypes are designated for Odynerus bellone Lepeletier, 1841 , Odynerus ( Odynerus ) aztecus de Saussure, 1857 and Odynerus ( Stenodynerus ) migonei Bertoni, 1926 .     

Mandipropamid targets the cellulose synthase-like PiCesA3 to inhibit cell wall biosynthesis in the oomycete plant pathogen, Phytophthora infestans

Oomycete plant pathogens cause a wide variety of economically and environmentally important plant diseases. Mandipropamid (MPD) is a carboxylic acid amide (CAA) effective against downy mildews, such as Plasmopara viticola on grapes and potato late blight caused by Phytophthora infestans . Historically, the identification of the mode of action of oomycete-specific control agents has been problematic. Here, we describe how a combination of biochemical and genetic techniques has been utilized to identify the molecular target of MPD in P. infestans . Phytophthora infestans germinating cysts treated with MPD produced swelling symptoms typical of cell wall synthesis inhibitors, and these effects were reversible after washing with H₂O. Uptake studies with ¹⁴C-labelled MPD showed that this oomycete control agent acts on the cell wall and does not enter the cell. Furthermore, ¹⁴C glucose incorporation into cellulose was perturbed in the presence of MPD which, taken together, suggests that the inhibition of cellulose synthesis is the primary effect of MPD. Laboratory mutants, insensitive to MPD, were raised by ethyl methane sulphonate (EMS) mutagenesis, and gene sequence analysis of cellulose synthase genes in these mutants revealed two point mutations in the PiCesA3 gene, known to be involved in cellulose synthesis. Both mutations in the PiCesA3 gene result in a change to the same amino acid (glycine-1105) in the protein. The transformation and expression of a mutated PiCesA3 allele was carried out in a sensitive wild-type isolate to demonstrate that the mutations in PiCesA3 were responsible for the MPD insensitivity phenotype.     

Isolation from a marching band increases haemocyte density in wild locusts (Chortoicetes terminifera)

1. The density‐dependent prophylaxis hypothesis predicts that individuals in high‐density populations will invest more resources in immune defence than individuals at lower densities. 2. However, recent work suggests that this prediction may not apply to all situations; solitarious species may paradoxically have higher scores than crowded counterparts in certain immune assays. 3. To investigate the relationship between a key immune parameter and field population densities, the total haemocyte counts (THCs) of Australian plague locusts (Chortoicetes terminifera) from three population densities in Western Australia were compared. 4. THCs were negatively correlated with field population densities, and locusts removed from a marching band and kept in isolation had increased THCs relative to group‐housed controls. 5. These results demonstrate that immune investment can inversely relate to population density in field conditions. 6. We suggest that isolated locusts increase their haemocyte densities relative to crowded conspecifics in response to potentially greater exposure to parasitoids and nematodes.     

Lizards and termites revisited

Abstract We evaluate the hypothesis, originally proposed for arid Australia, that abundant and diverse termite assemblages can promote lizard radiation, based on a reappraisal of published data and on new data from the Cerrado biome in central Brazil. We found a positive correlation between termite and lizard richness in Cerrado. However, termite abundance and richness cannot actively drive lizard speciation, but can be important in maintaining lizard richness. Cerrado shares with arid Australia a rich and abundant termite fauna, but local Cerrado lizard assemblages are relatively impoverished. We suggest that differences in lizard richness between Cerrado and arid Australia may be explained by a combination of variations in area and latitude controlling speciation rates and present‐day ecological factors moderating extinction rates.