Robust olfactory responses in the absence of odorant binding proteins

Odorant binding proteins (Obps) are expressed at extremely high levels in the antennae of insects,

and have long been believed essential for

carrying hydrophobic odorants to odor receptors

through the aqueous sensillar lymph. Previously

we constructed a map of the Drosophila antenna,

in which the abundant Obps are mapped to

olfactory sensilla with defined functions. Here we

have deleted all the Obp genes that are

abundantly expressed in the antennal basiconic

sensilla, which respond to fruit odors. We then

tested six functional types of sensilla

systematically in the mutants and found that all

respond robustly. Odors that are diverse in

chemical and temporal structures all elicited

strong responses. One sensillum that responds to

an odorant that affects oviposition gives a greater

physiological response following deletion

of Obp genes. Moreover, this mutant shows a

greater oviposition response to the odorant. Our

results support a model in which many sensilla

can respond to odorants in the absence of Obps,

and many Obps are not essential for olfactory

response, but that some Obps can modulate

olfactory physiology and the behavior that it

drives.