Plants in nature are faced with attack by potentially several hundred thousand species of herbivorous insects. Nevertheless, the world is still green, and any given plant species is resistant to attack by most insects. To a large extent, resistance to herbivory is mediated by a wide array of toxic and deterrent plant metabolites. Between- and within-species variation in the production of defensive chemicals often determines which plants a particular insect species is able to feed from. Some economically important plant toxins, e.g. nicotine in tobacco, have been studied extensively. However, the great majority of the defensive metabolites found in plants remain completely unknown. A typical leaf contains a few thousand different small molecules that can be detected by mass spectrometry, but only a few hundred of these have identified structures. It is likely that many of the as yet completely unknown plant metabolites function in defense against herbivores and/or pathogens.
The Jander lab studies the genetic and biochemical mechanisms that mediate plant interactions with insect herbivores. This includes not only the identification of novel defense-related plant metabolites, but also characterization of the genes and enzymes that are involved in their biosynthesis. Plant species that are currently being investigated include maize, Arabidopsis, and potato. Genetic mapping of natural variation in insect resistance, mass spectrometry-based screens to identify previously unknown plant defensive metabolites and characterization of biosynthetic enzymes through knockout mutations and in vitro enzyme assays have led to the discovery of novel plant defense mechanisms. On the insect side of the interaction, a major research focus is the investigation of strategies that herbivores use to avoid plant defenses or suppress them in a targeted manner.
The long-term goal of research on the chemical ecology of plant-insect interactions is to use the discoveries that are made in the laboratory to increase the natural resistance of crop plants to herbivore attack. Plants that are bred to have enhanced herbivore resistance would require fewer applications of potentially harmful pesticides, thereby providing benefits to the environment and reducing the input costs for farmers.
Examples of current research projects in the Jander lab are:
The Jander lab is collaborating with groups at the University of Bern, the Max Planck Institute for Chemical Ecology and Tel Aviv University to study the biosynthesis and function of benzoxazinoids. These indole-derived metabolites have a prominent role in the herbivore defenses of maize, wheat, rye and other grasses. Recent findings have included the discovery of previously unknown genes involved in maize benzoxazinoid biosynthesis, isolation of mutations that affect defense-induced benzoxazinoid production and evidence that there are defensive trade-offs in the production of different types of benzoxazinoids.
Although other insect herbivores are also being studied, maize-aphid interactions are a particular research emphasis of the Jander lab. Cultivated maize shows wide variation in its resistance to feeding by corn leaf aphids (Rhopalosiphum maidis). Whereas these aphids produce several progeny per day on some maize varieties, others are almost completely resistant to aphid attack. Genetic mapping of aphid progeny production on different maize inbred lines identified specific regions of the maize genome that influence this trait. In some cases, this genetic mapping approach has led to the discovery of specific maize genes and metabolites that provide aphid resistance.
The green peach aphid (Myzus persicae) is a focus of ongoing research in the Jander lab. As broad generalist herbivores, green peach aphids are exposed to a wide variety of defensive metabolites in the plant species from which they feed. Similar to the corn leaf aphid, the utilization of different host plants by the green peach aphid is often determined by the abundance of specific plant defensive metabolites. Analysis of aphid salivary proteins, which are injected into the plant as the insects are feeding, has demonstrated that some of these proteins are involved in suppressing plant defenses, whereas others are recognized by plants as signals to mount defense responses.
Plant-mediated RNA interference (RNAi), whereby double-stranded RNA targeting insect genes is produced in the plant, has potential applications as an aphid control method. Research conducted in collaboration with Angela Douglas’ lab at Cornell University showed that growth and reproduction of green peach aphids is reduced on Arabidopsis plants transformed with RNAi constructs that limited the expression of aphid osmoregulatory genes. Current research efforts are directed at identifying aphid-specific genes that can be used for RNAi-mediated control of green peach aphids, without affecting the growth and survival of beneficial insect species that might consume these aphids.
Potato metabolic changes induced by tuber moth feeding
When certain potato varieties are subjected to low-level infestation with the Guatemalan tuber moth (Tecia solanivora), there is a two-fold increase in the marketable yield of uninfested tubers on the same plants. Tuber growth changes are associated with increased dry mass of uninfested tubers on infested plants, rather than merely higher water content. Current research, in collaboration with Katja Poveda’s lab at Cornell University is focused on identifying alterations in potato photosynthesis, sugar transport and other aspects of primary metabolism that lead to increased starch deposition in the tubers of potato plants infested with the Guatemalan tuber moth.
- Now in its 16th year, BTI’s annual PGRP symposium provides a means for student interns to to present their findings in a professional, engaging setting. Read more »
- The research project, titled Viruses and Insects as Plant Enhancement Resources (VIPER), is supported by the Defense Advanced Research Projects Agency (DARPA) Insect Allies program. Read more »
- BTI’s Georg Jander is leading one of eight research groups selected to receive awards through the Enabling Discovery through Genomic Tools (EDGE) program, overseen by the National Science Foundation’s (NSF’s) Biological Science Directorate. Read more »
Genetic and biochemical mechanisms of plant defense against insects.
Plants in nature are subject to attack by wide variety of caterpillars, beetles, aphids, and other insect herbivores. Although there are a million or more species of herbivorous insects, any individual plant species is resistant to the vast majority of these. Insect feeding is inhibited by an array of chemical defenses that exhibits great variability both within and among different plant species. However, although it is known that any plant leaf contains several thousand different metabolites, most of these remain unidentified. In the Jander lab we are investigating natural variation in the herbivore resistance of maize, tomato, and potato to elucidate the molecular basis of plant defense traits. Through a combination of genetic crosses, gene expression assays, metabolite profiling, and insect growth experiments, we are able to identify specific plant genes, biosynthetic pathways, and metabolites that are required to mount an effective anti-herbivore defense.
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