Hence, Empoasca feeding damage to individual plants in native plant populations could be an indicator of natural genetic variation in defense responses. Therefore, the scientists studied three different naturally grown Nicotiana attenuata populations − a total of about 700 plants − over a period of two field seasons. They examined Empoasca damage in every single plant and found six infested plants. These plants were treated with oral secretions of the tobacco specialist Manduca sexta (tobacco hornworm), a treatment which triggers jasmonate-signaling. As a result, these plants showed a significantly lower jasmonate accumulation than uninfested control plants. Seeds of these plants were germinated and the offspring were again tested − with the same result. "Empoasca has identified for us valuable natural mutants for further experiments," says Ian Baldwin, leader of the study.
Because Nicotiana attenuata uses fires to synchronize its germination from long-lived seed banks to grow in dense populations characterized by intense intraspecific competition and variable herbivore pressures, the scientists hypothesize that growth-defense tradeoffs are likely severe for this plant species, and these tradeoffs likely provide the selective pressure to maintain these JA-signaling mutants occurring in native populations − despite the clear disadvantages of being defense-impaired. "Once we have completed the sequencing of the Nicotiana attenuata genome, we will characterize in greater detail these JA-
|Contact: Ian T. Baldwin|
Max Planck Institute for Chemical Ecology