Molecular elements of pheromone detection in the female moth, Heliothis virescens

Abstract

Pheromones play pivotal roles in the reproductive behavior of moths, most prominently for the mate finding of male moths. Accordingly, the molecular basis for the detection of female-released pheromones by male moths has been studied in great detail. In contrast, little is known about how females can detect pheromone components released by themselves or by conspecifics. In this study, we assessed the antenna of female Heliothis virescens for elements of pheromone detection. In accordance with previous findings that female antennae respond to the sex pheromone component (Z)-9-tetradecenal, we identified olfactory sensory neurons that express its cognate receptor, the receptor type HR6. All HR6 cells coexpressed the "sensory neuron membrane protein 1" (SNMP1) and were associated with supporting cells expressing the pheromone-binding proteins PBP1 and PBP2. These features are reminiscent to male antennae and point to congruent mechanisms for pheromone detection in the two sexes. Further analysis of the SNMP1-expressing cells revealed a higher number in females compared to males. Moreover, in females, the SNMP1 neurons were arranged in clusters, which project their dendrites into a common sensillum, whereas in males there were only solitary SNMP1-neurons and only 1 per sensillum. Not all SNMP1 positive cells in female antennae expressed HR6 but instead the putative pheromone receptors HR11 and HR18, respectively. Neurons expressing 1 of the 3 receptor types were assigned to different sensilla. Together the data indicate that on the antenna of females, sensory neurons in a subset of sensilla trichodea are equipped with molecular elements, which render them responsive to pheromones.

Insect Pheromone Receptors – Key Elements in Sensing Intraspecific Chemical Signals

“…Thus, sex pheromone information may be used by females to avoid places of high mating competition and unfavorable oviposition sites, thereby minimizing competition for ecological resources ( Harari and Steinitz, 2013 ; Holdcraft et al, 2016 ). In line with this notion, expression of PRs for female-released SPCs has been reported for the antennae of female moths ( Bengtsson et al, 2012 ; Sun et al, 2013 ; Holdcraft et al, 2016 ; Zielonka et al, 2017 ). For example, in female antennae of H. virescens that comprise trichoid sensilla tuned to the female-released SPC (Z)-9-tetradecenal ( Hillier et al, 2006 ), OSNs expressing the cognate PR type HR6 are located to this sensillum type ( Zielonka et al, 2017 ).…”

“…Furthermore, functional analysis of these ORs in heterologous expression systems confirmed their responsiveness to distinct SPCs ( Sakurai et al, 2004 ; Nakagawa et al, 2005 ; Grosse-Wilde et al, 2006 , 2007 ; Wang et al, 2011 ). Matching the predictions from single sensillum recordings of H. virescens ( Almaas and Mustaparta, 1991 ; Baker et al, 2004 ), expression of the OR types HR13 and HR6 responding to the major (HR13) and the minor (HR6) component of the female sex pheromone could be assigned to OSNs of pheromone-responsive trichoid sensilla classified as type A and type B, respectively ( Gohl and Krieger, 2006 ; Grosse-Wilde et al, 2007 ; Zielonka et al, 2017 ). Likewise, expression of the B. mori receptors BmOR1 and BmOR3 detecting the female-released SPCs bombykol and bombykal, respectively, was localized to the corresponding electrophysiologically characterized pairs of OSNs in sensilla trichodea of male silk moths ( Kaissling et al, 1978 ; Krieger et al, 2005 ; Nakagawa et al, 2005 ).…”

The role of SNMPs in insect olfaction

“…In the Drosophila antenna, DmelSNMP1 is expressed by each OSN of all trichoid sensilla with no apparent differences between sexes, whereas OSNs of sensilla basiconica or sensilla coeliconica are devoid of the protein (Benton et al 2007). In Heliothis virescens, HvirSNMP1 is present in OSNs innervating subsets of trichoid sensilla with sex-specific differences in the number of SNMP1-expressing OSNs per sensillum (Zielonka et al 2018, Blankenburg et al 2019. Remarkably, in females, all the 2-3 OSNs of the trichoid sensilla express HvirSNMP1, whereas in males, only a single cell of such a cluster possesses the protein (Zielonka et al 2018).…”

“…In Heliothis virescens, HvirSNMP1 is present in OSNs innervating subsets of trichoid sensilla with sex-specific differences in the number of SNMP1-expressing OSNs per sensillum (Zielonka et al 2018, Blankenburg et al 2019. Remarkably, in females, all the 2-3 OSNs of the trichoid sensilla express HvirSNMP1, whereas in males, only a single cell of such a cluster possesses the protein (Zielonka et al 2018). In males, the distribution of HvirSNMP1 cells matches the expression pattern of pheromone-sensitive ORs Krieger 2006, Zielonka et al 2018) and is complementary with electrophysiological recordings of male Heliothis virescens trichoid sensilla, demonstrating that only one OSN of the sensillum is tuned to pheromone components (Almaas andMustaparta 1991, Baker et al 2004).…”

“…In males, the distribution of HvirSNMP1 cells matches the expression pattern of pheromone-sensitive ORs Krieger 2006, Zielonka et al 2018) and is complementary with electrophysiological recordings of male Heliothis virescens trichoid sensilla, demonstrating that only one OSN of the sensillum is tuned to pheromone components (Almaas andMustaparta 1991, Baker et al 2004). HvirSNMP1-expressing neurons in females also express pheromone-sensitive ORs (Zielonka et al 2018), yet it is unknown whether all the SNMP1 cells of a given trichoid sensillum are tuned to pheromone components. Ultimately, these sex-specific expression patterns indicate differences in the functional impact of HvirSNMP1 between males and females of Heliothis virescens.…”