Using radioactive carbon and genetically modified native tobacco plants (Nicotiana attenuata), scientists at Max Planck Institutes in Jena and Golm (Potsdam) and at the Research Centre in JĂĽlich have discovered the first gene mediating tolerance to herbivore attack: GAL83, the beta-subunit of Nicotiana attenuataâ€
Ecological studies conducted in the department of Prof. Ian T. Baldwin at the Max Planck Institute for Chemical Ecology in Jena, Germany, focus on the defense of plants against attack from herbivores. Plants respond to attack by producing an arsenal of direct (toxins, digestibility reducers, etc.) and indirect defences that reduce the attackers' performance, thereby lessening the amount of damage inflicted to the plant. However, the co-evolutionary dynamics of the interaction often leads to herbivores that are adapted to the plantâ€
Wild tobacco, which is native to North America, has developed sophisticated methods to fend off Manduca sexta larvae. For example, jasmonic acid produced after insect attack elicits the emission of volatiles that attract Manduca sexta predators. These insect predators kill caterpillars (Kessler and Baldwin, 2001). Yet even such a complex defense system does not guarantee the plantsâ€
This seems to apply to carbon, too, which is assimilated from carbon dioxide during photosynthesis. As important energy source, carbon is commonly stored as sugar or starch. The scientists found that molecules in the oral secretions of Manduca sexta larvae activate the downregulation of the expression of a protein kinase activator (GAL83) in the plant tissue via a signalling cascade that remains unknown. GAL83 is not unknown in the animal kingdom and in microorganisms: it is the beta-subunit of a protein complex (SNF1 related kinases), which regulates the use of glucose or galactose in mammals and yeast - especially during times of energy deficiency. SNF1 kinases function as posttranslational modificators and can up- or downregulate the activity of metabolic enzymes by means of phosphorylation.
Prof. Baldwin and his coworkers identified GAL83 when they were examining changes in gene expression in young, photosynthetically active leaves that had been attacked by insect larvae. Using the differential RNA display method, they found remarkably few transcripts (mRNA) of GAL83 in the leaves attacked by insects. With the help of transgenic tobacco plants with constantly downregulated GAL83, they measured the same effect as in the nontransgenic, larvae-infested plants: the increased transport of carbon into the roots, and the utilization of this carbon for seed production at the end of development.
 Kessler and Baldwin, Science (2001): The enemy of my enemy is my friend, March 14, 2001
SNF-related kinases allow plants to tolerate herbivory by allocating carbon to roots. Jens Schwachtje, Peter E. H. Minchin, Sigfried Jahnke, Joost T. van Dongen, Ursula Schittko, Ian T. Baldwin PNAS (Early Edition) 2006; Vol. 103 (34), 12935-12940
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