This document discusses insect chemoreception and the role of chemoreceptor genes and proteins. It provides examples in three insect species: 1) Fruit flies (Drosophila melanogaster) have 60 odorant receptor genes that encode chemoreceptor proteins involved in smell. The Or83b protein mediates the function of other odorant receptors. 2) Honey bees (Apis mellifera) have over 165 odorant receptors that allow them to recognize diverse floral odors, important for locating flowers. 3) Tobacco budworm moths (Heliothus virescens) express chemoreceptors involved in host plant recognition, essential for finding food plants like tobacco. The chemorecept

1. Insect Chemoreception
Genomics and Plant-Environment Interaction
Jawwad Hassan Mirza
Ph.D. Scholar (Student ID# 435108485)
College of Food and Agriculture Sciences
King Saud University

2. Introduction
• Many types of Receptors
• Chemoreceptors, most important of all
• Chemosensory organ = SENSILLA
• Taste (Gustatory) and Smell (Olfactory) Receptors
• Involved in:
– Finding food
– Accessing food quality
– Identifying mates
– Searching for oviposition site
– Avoid toxins and predators
Buck and Axel 1991; Hallem et al, 2004

4. GUSTATORY RECEPTORS OLFACTORY RECEPTORS
ANTENNAE
MAXILLARY PALP
WINGS
OVIPOSITOR LEGS
MOUTH PARTS

5. Genomics of Insect
Chemoreception
Role of Genes and Receptors

6. REMEMBER!!
Chemoreceptor superfamily includes many Olfactory and
Gustatory Receptor Families
Robertson et al, 2003

7. CHEMORECEPTORS
• 60 Or and 60 Gr family genes , 130
chemoreceptor proteins in D. melanogaster
• Families of odorant and gustatory receptors are
evolutionarily related
• Four Gr genes are expressed in subsets of
neurons in the antenna and/or maxillary palp
• Antennal Grs if function as odorant receptors,
olfactory receptor function has evolved
separately several times within the superfamily
Scott et al, 2001; Dunipace et al, 2001

8. • Or83b is extremely divergent from the other
Or proteins and is expressed in most olfactory
receptor neurons
• The genes encoding these proteins are evenly
spread throughout the genome
• The amino acid differences between the Gr
and Or proteins extremely high
– Evolving need to adapt to new ecological niches
Scott et al, 2001; Dunipace et al, 2001

9. OLFACTORY RECEPTORS

10. OLFACTORY RECEPTORS
• Olfactory Receptor Neurons (ORNs) express a single Olfactory Receptor
protein (Or)
• Each ORN expressing a particular Or converges on a single glomerulus in
each antennal lobe
• Allow activation of glomeruli interpreted as a particular odor
Hallem et al, 2006

11. 1. FRUIT FLY (Drosophila melanogaster)
• 1st Insect OR discovered (62 ORs by 60 genes)
• 7 transmembrane (7TM) domains with
G-protein coupled receptors (GPCRs)
• DmOr83b mediate function of other ORs in ORN
• DmOr83b determines:
– Odor response profile
– Spontaneous firing rate
– Response dynamics
– Signaling mode
Hallem et al, 2006

12. 2. HONEY BEE (Apis mellifera)
• Locating Flower and Social Communication
• Visit the same flower with 90% success
• Use Olfactory Receptors at Antennae
• Glomeruli = 165 (far more than any other insect)
– large number of receptors
• AmOr2 = ortholog of DmOr83b

13. • Genome encodes 165 functional ORs
• Allow bees to recognize diverse floral odor
• Huge number ORs relates to co-evolution of
BEES and ANGIOSPERMS
• 16,000 ORs in Drones, 2700 ORs in workers
Brockmann and Brückner, 2001

14. 3. MOTHS (Heliothus virescens)
• Recognition of odor by specialized sensory neurons
• Transduce the chemical signal into an electrical
neuronal response
• Wire the olfactory information from the periphery to
the antennal lobes
• Transduction process via the G protein-controlled PLC
• Chemicals cause reaction of hydrolysis of
phosphatidylinositol (PIP2) and the formation of
second messengers (inositol triphosphate and
diacylglycerol)
Steinbrecht, 1999

15. • The HR5 receptor is expressed in sensory
neurons located in the vicinity of sensory hairs
comprise contact-chemoreceptors, first
presumed gustatory receptor of moth.
• All receptor types expressed in the antennae
of males and females, involved in the
detection of general odors
• High number and diversity of receptor to
perceive the broad spectrum of plant-derived
odors
• Essential for this insect to find its host plants,
such as tobacco, cotton, soybean and
sunflower
Matthews and Tunstall, 1994

16. GUSTATORY RECEPTORS
• Anterior wing margin, the chemosensory
sensilla harbour gustatory receptors in D.
melanogastor
• Group of 7TM-domain candidate GPCRs were
identified in the D. melanogaster genome.
• expressed in gustatory organs such as the mouthparts
• 68 GRs by 60 genes
• GRs sometime work as Ors
Clyne et al, 2000

17. SEM of D. melanogaster wing anterior margin

18. • IN BEES, GR family is not diverse because:
– angiosperms not evolved the pollens/nectors
– Larvae in hive fed by adults
– mostly use antenna to touch objects

19. Insect Chemoreception
Interaction with Plants and Environment

20. THEORIES OF HOST SELECTION
• Brues (1920)proposed a “BOTANICAL INSTINCT THEORY”,
“insects select host plants that meet specific
nutritional and ecological requirements for that
insect not offered by other plant species”
• Fraenkel (1959)proposed “THE TOKEN STIMULI THEORY”,
“insect host plant selection is determined by
specific secondary plant substances or
phytochemicals, i.e. glycosides, phenols, tannins,
alkaloids, terpenoids, and saponins.”
Matthews and Tunstall, 1994

21. PLANTS vs INSECTS
• Important component of an ecosystem
• Plants release chemicals for insects:
– To attract (for pollination, for predation)
– To repel (self defense)
• Honey bees vs Flowering Plants
• Tobacco Plant vs Tobacco budworm
Matthews and Tunstall, 1994

22. • Plants chemically respond differently for both
the abiotic and biotic injuries
• Plant release chemical when under attack by
phytophagous pests warning neighboring
plants.
Matthews and Tunstall, 1994

23. WHAT WE LEARNED!
• Chemoreception is vital for insect survival
• Manipulation for pest control
• Better Bio-agents and Enhanced crop productivity

24. References
• Hallem E.A., Dahanukar A., Carlson J.R., Dahanukar A., Carlson J.R., Carlson J.R., 2006. Insect
odor and taste receptors. Annu. Rev. Entomol. 51: 113–135.
• Hallem EA, Nicole Fox A, Zwiebel LJ, Carlson JR, 2004. Olfaction: mosquito receptor for
human-sweat odorant. Nature. 427:212-213.
• Clyne P.J., Warr C.G., Carlson J.R., Warr C.G., Carlson J.R., Carlson J.R., 2000. Candidate taste
receptors in Drosophila. Science. 287:1830–1834.
• Robertson H.M., Warr C.G., Carlson J.R., Warr C.G., Carlson J.R., Carlson J.R., 2003. Molecular
evolution of the insect chemoreceptor superfamily in Drosophila melanogaster . Proc. Natl.
Acad. Sci. 100:14537–14542.
• Brockmann A., Brückner D., 2001. Structural differences in the drone olfactory system of two
phylogenetically distant Apis species, A. florea and A. mellifera. Naturwissenschaften. 88:78–
81.
• Buck L, Axel R, 1991. A novel multigene family may encode odorant receptors: a molecular
basis for odor recognition. Cell, 65, 175–187.
• Scott, K., Brady, R., Jr., Cravchik, A., Morozov, P., Rzhetsky, A., Zuker, C. & Axel, R., 2001. Cell
104, 661–673.
• Dunipace, L., Meister, S., McNealy, C. & Amrein, H., 2001 Curr. Biol. 11, 821–835.
• Matthews, G.A. & Tunstall, J.P., 1994. Insect Pests of Cotton. CAB International, Wallingford,
UK.
• Steinbrecht, R., 1999. Olfactory receptors. In Eguchi, E. & Tominaga, Y. (eds), Atlas of
Arthropod Sensory Receptors. V. Springer, Tokyo.

25. THANK YOU FOR YOUR TIME
QUESTIONS ARE INVITED