Effector proteins that modulate plant--insect interactions.

Arthropod-resistant crops provide significant ecological and economic benefits to global agriculture. Incompatible interactions involving resistant plants and avirulent pest arthropods are mediated by constitutively produced and arthropod-induced plant proteins and defense allelochemicals synthesized by resistance gene products. Cloning and molecular mapping have identified the Mi-1.2 and Vat arthropod resistance genes as CC-NBS-LRR (coiled coil-nucleotide binding site-leucine rich repeat) subfamily NBS-LRR resistance proteins, as well as several resistance gene analogs. Genetic linkage mapping has identified more than 100 plant resistance gene loci and linked molecular markers used in cultivar development. Rice and sorghum arthropod-resistant cultivars and, to a lesser extent, raspberry and wheat cultivars are components of integrated pest management (IPM) programs in Asia, Australia, Europe, and North America. Nevertheless, arthropod resistance in most food and fiber crops has not been integrated due primarily to the application of synthetic insecticides. Plant and arthropod genomics provide many opportunities to more efficiently develop arthropod-resistant plants, but integration of resistant cultivars into IPM programs will succeed only through interdisciplinary collaboration.

Molecular Bases of Plant Resistance to Arthropods

Host plant resistance to aphids in cultivated crops: genetic and molecular bases, and interactions with aphid populations.

Aphids damage major world food and fiber crops through direct feeding and transmission of plant viruses. Fortunately, the development of many aphid-resistant crop plants has provided both ecological and economic benefits to food production. Plant characters governing aphid host selection often dictate eventual plant resistance or susceptibility to aphid herbivory, and these phenotypic characters have been successfully used to map aphid resistance genes. Aphid resistance is often inherited as a dominant trait, but is also polygenic and inherited as recessive or incompletely dominant traits. Most aphid-resistant cultivars exhibit constitutively expressed defenses, but some cultivars exhibit dramatic aphid-induced responses, resulting in the overexpression of large ensembles of putative aphid resistance genes. Two aphid resistance genes have been cloned. Mi-1.2, an NBS-LRR gene from wild tomato, confers resistance to potato aphid and three Meloidogyne root-knot nematode species, and Vat, an NBS-LRR gene from melon, controls resistance to the cotton/melon aphid and to some viruses. Virulence to aphid resistance genes of plants occurs in 17 aphid species--more than half of all arthropod biotypes demonstrating virulence. The continual appearance of aphid virulence underscores the need to identify new sources of resistance of diverse sequence and function in order to delay or prevent biotype development.

Plant resistance to aphid feeding: behavioral, physiological, genetic and molecular cues regulate aphid host selection and feeding

Damage by the Russian wheat aphid (RWA), Diuraphis noxia, significantly reduces wheat and barley yields worldwide. In compatible interactions, virulent RWA populations flourish and susceptible plants suffer extensive leaf chlorophyll loss. In incompatible interactions, RWA reproduction and population growth are significantly reduced and RWA-related chlorophyll loss in resistant plants is minor. The objectives of this study were to develop an understanding of the molecular and phytochemical bases of RWA resistance in plants containing the Dnx resistance gene. Microarray, real-time polymerase chain reaction, and phytohormone assays were conducted to identify transcriptome components unique to RWA-infested Dnx plants and susceptible (Dn0) plants, and to identify and characterize putative genes involved in Dnx plant defense responses. We found that RWA-infested Dnx plants upregulated >180 genes related to reactive oxygen species, signaling, pathogen defense, and arthropod allelochemical and physical defense. The expression of several of these genes in RWA-infested Dnx plants increased significantly from 6- to 24-h post infestation (hpi), but their expression in Dn0 plants, when present, was delayed until 48- to 96 hpi. Concentrations of 16- and 18-carbon fatty acids, trans-methyl-12-oxophytodienoic acid, and abscisic acid were significantly greater in Dnx foliage than in Dn0 foliage after RWA infestation, suggesting that Dnx RWA defense and resistance genes may be regulated via the oxylipin pathway. These findings provide a foundation for the elucidation of the molecular basis for compatible- and incompatible plant-aphid interactions.

/pdf/aphid-feeding-activates-expression-of-a-transcriptome-of-5btw6fze4w.pdf

Aphid Feeding Activates Expression of a Transcriptome of Oxylipin-based Defense Signals in Wheat Involved in Resistance to Herbivory

Breeding Wheat for Resistance to Insects

A new species, Collyria catoptron, is described from Gansu Province, China. It is an egg-larval koinobiont parasitoid reared from Cephus fumipennis, a grass-mining sawfly that attacks wheat. Collyria catoptron is currently being evaluated as a possible biological control agent for Cephus cinctus in North America.

A New Species of Collyria Schiødte (Hymenoptera: Ichneumonidae: Collyriinae), a Parasitoid of Cephus Fumipennis (Hymenoptera: Cephidae) in China, and Potential Biological Control Agent for Cephus Cinctus in North America

Many pest and beneficial insects overwinter as larvae in a state of diapause, with development resuming in the spring. In these cases, rates of post-diapause development of parasitoids must be synchronised with the vulnerable life stages of their hosts. Phenological asynchrony between introduced parasitoids and their targeted hosts has limited the success of some biological control efforts. Here, we assess the potential synchrony between Collyria catoptron Wahl (Hymenoptera: Ichneumonidae), a parasitoid of the Chinese wheat stem sawfly, Cephus fumipennis Eversmann (Hymenoptera: Cephidae), which is being considered as a biological control against a novel host species, Cephus cinctus Norton, in North America. We compared development timing and emergence patterns of both native and exotic species of sawflies with that of the parasitoid. We found that the mean number of days between termination of larval diapause and adult eclosion varied by less than one day across species, and patterns of emergence were also similar. The rate of development of this egg-larval parasitoid was within the range necessary to attack C. cinctus eggs. Furthermore, the development of C. cinctus from western Montana, United States of America most closely matched that of the parasitoid, suggesting western Montana as a possible release area.

https://www.fs.fed.us/rm/pubs_journals/2016/rmrs_2016_rand_t001.pdf

Assessing phenological synchrony between the Chinese sawfly, Cephus fumipennis, its egg-larval parasitoid, Collyria catoptron, and the North American sawfly, Cephus cinctus: Implications for biological control

Thomas G. Shanower

Papers

Breeding Wheat for Resistance to Insects

A New Species of Collyria Schiødte (Hymenoptera: Ichneumonidae: Collyriinae), a Parasitoid of Cephus Fumipennis (Hymenoptera: Cephidae) in China, and Potential Biological Control Agent for Cephus Cinctus in North America

Assessing phenological synchrony between the Chinese sawfly, Cephus fumipennis, its egg-larval parasitoid, Collyria catoptron, and the North American sawfly, Cephus cinctus: Implications for biological control