Correlation between Binding Affinity and Necrosis-Inducing Activity of Mutant AVR9 Peptide Elicitors1

The race-specific peptide elicitor AVR9 of the fungus Cladosporium fulvum induces a hypersensitive response only in tomato (Lycopersicon esculentum) plants carrying the complementary resistance gene Cf-9 (MoneyMaker-Cf9). A binding site for AVR9 is present on the plasma membranes of both resistant and susceptible tomato genotypes. We used mutant AVR9 peptides to determine the relationship between elicitor activity of these peptides and their affinity to the binding site in the membranes of tomato. Mutant AVR9 peptides were purified from tobacco (Nicotiana clevelandii) inoculated with recombinant potato virus X expressing the corresponding avirulence gene Avr9. In addition, several AVR9 peptides were synthesized chemically. Physicochemical techniques revealed that the peptides were correctly folded. Most mutant AVR9 peptides purified from potato virus X::Avr9-infected tobacco contain a single N-acetylglucosamine. These glycosylated AVR9 peptides showed a lower affinity to the binding site than the nonglycosylated AVR9 peptides, whereas their necrosis-inducing activity was hardly changed. For both the nonglycosylated and the glycosylated mutant AVR9 peptides, a positive correlation between their affinity to the membrane-localized binding site and their necrosis-inducing activity in MoneyMaker-Cf9 tomato was found. The perception of AVR9 in resistant and susceptible plants is discussed.

A Carboniferous insect gall: insight into early ecologic history of the Holometabola.

Although the prevalence or even occurrence of insect herbivory during the Late Carboniferous (Pennsylvanian) has been questioned, we present the earliest-known ecologic evidence showing that by Late Pennsylvanian times (302 million years ago) a larva of the Holometabola was galling the internal tissue of Psaronius tree-fern fronds. Several diagnostic cellular and histological features of these petiole galls have been preserved in exquisite detail, including an excavated axial lumen filled with fecal pellets and comminuted frass, plant-produced response tissue surrounding the lumen, and specificity by the larval herbivore for a particular host species and tissue type. Whereas most suggestions over-whelmingly support the evolution of such intimate and reciprocal plant-insect interactions 175 million years later, we provide documentation that before the demise of Pennsylvanian age coal-swamp forests, a highly stereotyped life cycle was already established between an insect that was consuming internal plant tissue and a vascular plant host responding to that herbivory. This and related discoveries of insect herbivore consumption of Psaronius tissues indicate that modern-style herbivores were established in Late Pennsylvanian coal-swamp forests.

Class 3 Hox genes in insects and the origin of zen.

We have cloned, from a beetle and a locust, genes that are homologous to the class 3 Hox genes of vertebrates. Outside the homeobox they share sequence motifs with the Drosophila zerknüllt (zen) and z2 genes, and like zen, are expressed only in extraembryonic membranes. We conclude that the zen genes of Drosophila derive from a Hox class 3 sequence that formed part of the common ancestral Hox cluster, but that in insects this (Hox) gene has lost its role in patterning the anterio-posterior axis of the embryo, and acquired a new function. In the lineage leading to Drosophila, the zen genes have diverged particularly rapidly.

A mechanism for inducing plant development: the genesis of a specific inhibitor.

Parasitic strategies are widely distributed in the plant kingdom and frequently involve coupling parasite organogenesis with cues from the host. In Striga asiatica, for example, the cues that initiate the development of the host attachment organ, the haustorium, originate in the host and trigger the transition from vegetative to parasitic mode in the root meristem. This system therefore offers a unique opportunity to study the signals and mechanisms that control plant cell morphogenesis. Here we establish that the biological activity of structural analogs of the natural inducer displays a marked dependence on redox potential and suggest the existence of a semiquinone intermediate. Building on chemistry that exploits the energetics of such an intermediate, cyclopropyl-p-benzoquinone (CPBQ) is shown to be a specific inhibitor of haustorial development. These data are consistent with a model where haustorial development is initiated by the completion of a redox circuit.

Vip3A, a novel Bacillus thuringiensis vegetative insecticidal protein with a wide spectrum of activities against lepidopteran insects.

A novel vegetative insecticidal gene, vip3A(a), whose gene product shows activity against lepidopteran insect larvae including black cutworm (Agrotis ipsilon), fall armyworm (Spodoptera frugiperda), beet armyworm (Spodoptera exigua), tobacco budworm (Heliothis virescens), and corn earworm (Helicoverpa zea) has been isolated from Bacillus thuringiensis strain AB88. VIP3-insecticidal gene homologues have been detected in approximately 15% of Bacillus strains analyzed. The sequence of the vip3A(b) gene, a homologue of vip3A(a) isolated from B. thuringiensis strain AB424 is also reported. Vip3A(a) and (b) proteins confer upon Escherichia coli insecticidal activity against the lepidopteran insect larvae mentioned above. The sequence of the gene predicts a 791-amino acid (88.5 kDa) protein that contains no homology with known proteins. Vip3A insecticidal proteins are secreted without N-terminal processing. Unlike the B. thuringiensis 5-endotoxins, whose expression is restricted to sporulation, Vip3A insecticidal proteins are expressed in the vegetative stage of growth starting at mid-log phase as well as during sporulation. Vip3A represents a novel class of proteins insecticidal to lepidopteran insect larvae.

Molecular cloning of a preprohormone from sea anemones containing numerous copies of a metamorphosis-inducing neuropeptide: a likely role for dipeptidyl aminopeptidase in neuropeptide precursor processing.

Neuropeptides are an important group of hormones mediating or modulating neuronal communication. Neuropeptides are especially abundant in evolutionarily "old" nervous systems, such as those of cnidarians, the lowest animal group having a nervous system. Cnidarians often have a life cycle including a polyp, a medusa, and a planula larva stage. Recently, a neuropeptide, < Glu-Gln-Pro-Gly-Leu-Trp-NH2, has been isolated from sea anemones that induces metamorphosis in a hydroid planula larva to become a hydropolyp [Leitz, T., Morand, K. & Mann, M. (1994) Dev. Biol. 163, 440-446]. Here, we have cloned the precursor protein for this metamorphosis-inducing neuropeptide from sea anemones. The precursor protein is 514-amino acid residues long and contains 10 copies of the immature, authentic neuropeptide (Gln-Gln-Pro-Gly-Leu-Trp-Gly). All neuropeptide copies are preceded by Xaa-Pro or Xaa-Ala sequences, suggesting a role for dipeptidyl aminopeptidase in neuropeptide precursor processing. In addition to these neuropeptide copies, there are 14 copies of another, closely related neuropeptide sequence (Gln-Asn-Pro-Gly-Leu-Trp-Gly). These copies are flanked by basic cleavage sites and, therefore, are likely to be released from the precursor protein. Furthermore, there are 13 other, related neuropeptide sequences having only small sequence variations (the most frequent sequence: Gln-Pro-Gly-Leu-Trp-Gly, eight copies). These variants are preceded by Lys-Arg, Xaa-Ala, or Xaa-Pro sequences, and are followed by basic cleavage sites, and therefore, are also likely to be produced from the precursor. Thus, there are at least 37 closely related neuropeptides localized on the precursor protein, making this precursor one of the most productive preprohormones known so far. This report also shows that unusual processing sites are common in cnidarian preprohormones.