Insect ChemoreceptionGenomics and Plant-Environment Interaction

Jawwad Hassan MirzaPh.D. Scholar (Student ID# 435108485)

College of Food and Agriculture SciencesKing Saud University

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

GUSTATORY RECEPTORS OLFACTORY RECEPTORS

ANTENNAE

MAXILLARY PALP

WINGS

OVIPOSITOR LEGS

MOUTH PARTS

Genomics of Insect Chemoreception

Role of Genes and Receptors

REMEMBER!!Chemoreceptor superfamily includes many Olfactory and

Gustatory Receptor Families

Robertson et al, 2003

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

• 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

OLFACTORY RECEPTORS

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

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

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

• 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

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

• 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

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

SEM of D. melanogaster wing anterior margin

• 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

Insect Chemoreception Interaction with Plants and Environment

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

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

• 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

WHAT WE LEARNED!

• Chemoreception is vital for insect survival

• Manipulation for pest control

• Better Bio-agents and Enhanced crop productivity

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.

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