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Schlagwörter:
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Zusammenfassung:
Optimal defense (OD) theory predicts that within a plant, tissues are defended in proportion to their fitness value and risk of
predation. The fitness value of leaves varies greatly and leaves are protected by jasmonate (JA)-inducible defenses. Flowers are
vehicles of Darwinian fitness in flowering plants and are attacked
by herbivores and pathogens, but how they are defended is rarely
investigated. We used Nicotiana attenuata, an ecological model
plant with well-characterized herbivore interactions to characterize
defense responses in flowers. Early floral stages constitutively
accumulate greater amounts of two well-characterized defensive
compounds, the volatile (E)-α-bergamotene and trypsin proteinase
inhibitors (TPIs), which are also found in herbivore-induced leaves.
Plants rendered deficient in JA biosynthesis or perception by RNA
interference had significantly attenuated floral accumulations of
defensive compounds known to be regulated by JA in leaves. By
RNA-seq, we found a JAZ gene, NaJAZi, specifically expressed in
early-stage floral tissues. Gene silencing revealed that NaJAZi functions
as a flower-specific jasmonate repressor that regulates JAs,
(E)-α-bergamotene, TPIs, and a defensin. Flowers silenced in NaJAZi
are more resistant to tobacco budworm attack, a florivore. When
the defensin was ectopically expressed in leaves, performance of
Manduca sexta larvae, a folivore, decreased. NaJAZi physically interacts
with a newly identified NINJA-like protein, but not the canonical
NINJA. This NINJA-like recruits the corepressor TOPLESS
that contributes to the suppressive function of NaJAZi on floral
defenses. This study uncovers the defensive function of JA signaling
in flowers, which includes components that tailor JA signaling
to provide flower-specific defense.
