Making weed biological control predictable,safer and more effective: perspectives from New Zealand

A persistent problem in weed biocontrol is how to reliably predict whether a plant that supports development in laboratory host-specificity testing will be utilized in field conditions, and this is undoubtedly preventing releases of safe and effective agents. Moreover, the potential for unanticipated undesirable indirect effects of weed biocontrol on ecological networks has raised concerns by policy-makers and the general public. The key to minimizing risks of non-target impacts is prioritizing candidate agents that are both host-specific and effective, such that the number of agents required to bring the weed under control is minimized. As a consequence both the weed and its biocontrol agents become minor components of the local biota. Here we review recent attempts in New Zealand to improve the predictive ability of host-range testing, to avoid potentially safe and effective agents being rejected. Research in New Zealand aimed at predicting whether an agent is likely to experience enemy-release (i.e. reduced parasitism and predation) could assist agent prioritization, potentially making biocontrol both environmentally safer and more effective.     

Scale and direction of adaptive introgression between black cottonwood (Populus trichocarpa) and balsam poplar (P. balsamifera)

Introgression can introduce novel genetic variation at a faster rate than mutation alone and result in adaptive introgression when adaptive alleles are maintained in the recipient genome over time by natural selection. A previous study from our group demonstrated adaptive introgression from Populus balsamifera into P. trichocarpa in a target genomic region. Here we expand our local ancestry analysis to the whole genome of both parents to provide a comprehensive view of introgression patterns and to identify additional candidate regions for adaptive introgression genomewide. Populus trichocarpa is a large, fast‐growing tree of mild coastal regions of the Pacific Northwest, whereas P. balsamifera is a smaller stature tree of continental and boreal regions with intense winter cold. The species hybridize where they are parapatric. We detected asymmetric patterns of introgression across the whole genome of these two poplar species adapted to contrasting environments, with stronger introgression from P. balsamifera to P. trichocarpa than vice versa. Admixed P. trichocarpa individuals contained more genomic regions with unusually high levels of introgression (19 regions) and also the largest introgressed genome fragment (1.02 Mb) compared with admixed P. balsamifera (nine regions). Our analysis also revealed numerous candidate regions for adaptive introgression with strong signals of selection, notably related to disease resistance, and enriched for genes that may play crucial roles in survival and adaptation. Furthermore, we detected a potential overrepresentation of subtelomeric regions in P. balsamifera introgressed into P. trichocarpa and possible protection of sex‐determining regions from interspecific gene flow.     

Forum – Taxonomic Stability is Ignorance

Absolute nomenclatural stability is undesirable in phylogenetic classifications because they reflect changing hypotheses of cladistic relationships. De Queiroz and Gauthier's (1990: Syst. Zool. 39, 307–322; 1992: A. Rev. Ecol. Syst. 23, 449–480; 1994: Trends Ecol. Evol. 9, 27–31) alternative to Linnaean nomenclature is concluded to provide stable names for unstable concepts. In terms of communicating either characters shared by species of a named taxon or elements (species) included in a taxon, de Queiroz and Gauthier's system is less stable than the Linnaean system. Linnaean ranks communicate limited information about inclusivity of taxa, but abandonment of ranks results in the loss of such information. As cladistic hypotheses advance, taxa named under de Queiroz and Gauthier's system can change their level of generality radically, from being part of a group to including it, without any indicative change in its spelling. The Linnaean system has been retained by taxonomists because its hierarchic ranks are logically compatible with nested sets of species, monophyletic groups, and characters. Other authors have offered conventions to increase the cladistic information content of Linnaean names or to replace them with names that convey cladistic knowledge in greater detail; de Queiroz and Gauthier sacrifice the meaning of taxon names and categorical ranks in favor of spelling stability.     

The metabolic role and evolution of L-arabinitol 4-dehydrogenase of Hypocrea jecorina.

L-Arabinitol 4-dehydrogenase (Lad1) of the cellulolytic and hemicellulolytic fungus Hypocrea jecorina (anamorph: Trichoderma reesei) has been implicated in the catabolism of L-arabinose, and genetic evidence also shows that it is involved in the catabolism of D-xylose in xylitol dehydrogenase (xdh1) mutants and of D-galactose in galactokinase (gal1) mutants of H. jecorina. In order to identify the substrate specificity of Lad1, we have recombinantly produced the enzyme in Escherichia coli and purified it to physical homogeneity. The resulting enzyme preparation catalyzed the oxidation of pentitols (L-arabinitol) and hexitols (D-allitol, D-sorbitol, L-iditol, L-mannitol) to the same corresponding ketoses as mammalian sorbitol dehydrogenase (SDH), albeit with different catalytic efficacies, showing highest k(cat)/K(m) for L-arabinitol. However, it oxidized galactitol and D-talitol at C4 exclusively, yielding L-xylo-3-hexulose and D-arabino-3-hexulose, respectively. Phylogenetic analysis of Lad1 showed that it is a member of a terminal clade of putative fungal arabinitol dehydrogenase orthologues which separated during evolution of SDHs. Juxtapositioning of the Lad1 3D structure over that of SDH revealed major amino acid exchanges at topologies flanking the binding pocket for d-sorbitol. A lad1 gene disruptant was almost unable to grow on L-arabinose, grew extremely weakly on L-arabinitol, D-talitol and galactitol, showed reduced growth on D-sorbitol and D-galactose and a slightly reduced growth on D-glucose. The weak growth on L-arabinitol was completely eliminated in a mutant in which the xdh1 gene had also been disrupted. These data show not only that Lad1 is indeed essential for the catabolism of L-arabinose, but also that it constitutes an essential step in the catabolism of several hexoses; this emphasizes the importance of such reductive pathways of catabolism in fungi.     

Selective photoreactions in a programmable array microscope (PAM): photoinitiated polymerization, photodecaging, and photochromic conversion.

BACKGROUND: Innovative thinking and experimentation were the hallmarks of Mack Fulwyler's approach to research. This report summarizes some of the ideas and their early realizations that he pursued in the field of imaging cytometry, work that was not published before his untimely death, although he composed the initial draft of this report. METHODS: Included are related experiments implemented in the programmable array microscope (PAM) devised for patterned illumination and detection, the instrument that Mack Fulwyler employed during a sabbatical leave in G?ttingen in 1998. Despite being the originator of instrumentation for flow cytometry and sorting, Mack Fulwyler was intensely interested in imaging systems, recognizing their ability to resolve cellular details obscured by the whole cell signals generally acquired in flow. At one point, these interests merged with those of two other authors (I.T.Y. and T.M.J.), leading to the Image Cytometry and Sorting (ICAS) strategy and project. A major goal was uncomplicated rare cell detection and isolation using a sequential process of cellular labeling via suitable probes, whole field imaging, and selective area-restricted photoinduced reactions designed to encapsulate and/or chemically or physically tag cells in a manner permitting subsequent fractionation by bulk techniques. RESULTS AND CONCLUSION: This publication features photoinduced polymerization, photodecaging, photoactivation, and photochromic conversion reactions carried out by Fulwyler and/or the other authors with the PAM, employing operator designated patterns and locations in various samples. Photopolymerization of polyethylene glycol-diacrylate to a gel-like structure allowing the specific selection of objects (cells) for further analysis and processing techniques was the approach explored personally by Mack Fulwyler in relation to the ICAS concept.     

Role of Phosphorylation in Moesin Interactions with PIP2-Containing Biomimetic Membranes

Moesin, a protein of the ezrin, radixin, and moesin family, which links the plasma membrane to the cytoskeleton, is involved in multiple physiological and pathological processes, including viral budding and infection. Its interaction with the plasma membrane occurs via a key phosphoinositide, the phosphatidyl(4,5)inositol-bisphosphate (PIP₂), and phosphorylation of residue T558, which has been shown to contribute, in cellulo, to a conformationally open protein. We study the impact of a double phosphomimetic mutation of moesin (T235D, T558D), which mimics the phosphorylation state of the protein, on protein/PIP₂/microtubule interactions. Analytical ultracentrifugation in the micromolar range showed moesin in the monomer and dimer forms, with wild-type (WT) moesin containing a slightly larger fraction (～30%) of dimers than DD moesin (10–20%). Only DD moesin was responsive to PIP₂ in its micellar form. Quantitative cosedimentation assays using large unilamellar vesicles and quartz crystal microbalance on supported lipid bilayers containing PIP₂ reveal a specific cooperative interaction for DD moesin with an ability to bind two PIP₂ molecules simultaneously, whereas WT moesin was able to bind only one. In addition, DD moesin could subsequently interact with microtubules, whereas WT moesin was unable to do so. Altogether, our results point to an important role of these two phosphorylation sites in the opening of moesin: since DD moesin is intrinsically in a more open conformation than WT moesin, this intermolecular interaction is reinforced by its binding to PIP₂. We also highlight important differences between moesin and ezrin, which appear to be finely regulated and to exhibit distinct molecular behaviors.