Abstract
Genetic variation within and among populations provides the raw material for evolution. Although many studies describe inter- and intraspecific variation of defensive metabolites, little is known about variation among plant populations within early signaling responses elicited by herbivory or by herbivore oral secretions (OS) introduced into wounds during feeding. In this study, we compare the OS-elicited early responses as well as the antiherbivore defensive metabolites in two accessions of the wild tobacco Nicotiana attenuata and show that, compared with an accession collected from Utah, an Arizona accession has lower herbivore-elicited activity of the salicylic acid-induced protein kinase, an important mitogen-activated protein kinase involved in herbivore resistance. These differences in salicylic acid-induced protein kinase activity were associated with substantially different levels of OS-elicited jasmonic acid, jasmonic acid-isoleucine conjugate, and ethylene bursts. Gene expression level polymorphism (ELP) determines phenotypic variation among populations, and we found the two accessions to have significantly different ELPs in the genes involved in early signaling responses to herbivory. In addition, we found differences between the Utah and the Arizona accessions in the concentrations of several secondary metabolites that contribute to N. attenuata's direct and indirect defenses. This study demonstrates significant natural variation in regulatory elements that mediate plant responses to herbivore attack, highlighting the role of ELP in producing a diversity of plant defense phenotypes.
Highlights
Genetic variation within and among populations provides the raw material for evolution
The moment M. sexta begins to feed, a cascade of signaling events leads to increased defense levels (Fig. 1); N. attenuata plants recognize herbivory-specific elicitors derived from M. sexta oral secretions (OS), namely, fatty acidamino acid conjugates (FACs), and quickly activate mitogen-activated protein kinase (MAPK) signaling and, subsequently, jasmonic acid (JA)- and ethylene (ET)-mediated defense responses (Kahl et al, 2000; Halitschke and Baldwin, 2003; Wu et al, 2007a)
We examined the early herbivoreinduced responses in two N. attenuata accessions collected from Utah and Arizona
Summary
Genetic variation within and among populations provides the raw material for evolution. The moment M. sexta begins to feed, a cascade of signaling events leads to increased defense levels (Fig. 1); N. attenuata plants recognize herbivory-specific elicitors derived from M. sexta oral secretions (OS), namely, fatty acidamino acid conjugates (FACs), and quickly activate mitogen-activated protein kinase (MAPK) signaling and, subsequently, JA- and ethylene (ET)-mediated defense responses (Kahl et al, 2000; Halitschke and Baldwin, 2003; Wu et al, 2007a) These include: (1) a highly reconfigured transcriptome that encompasses changes in transcript levels of defense- and growthrelated genes; (2) the release of volatile organic compounds (VOCs) that function as an indirect defense; and (3) the accumulation of herbivore-deterrent or -damaging
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