The ABC transporter ABCH-9C is needed for cuticle barrier construction in Locusta migratoria.

ATP-binding cassette (ABC) transporters constitute a large superfamily of proteins that mediate transport of a diverse number of substrates including nutrients, lipids and xenobiotics across membranes serving a variety of developmental and physiological functions. Here, we report on the molecular properties and biological roles of the ABC transporter LmABCH-9C in the migratory locust Locusta migratoria. LmABCH-9C was expressed continuously during nymphal development in all tissues including the integument. Expression was highest just after molting. Suppression of LmABCH-9C transcript levels by RNA interference (RNAi) in nymphs provoked death during or soon after molting to the next stage. These nymphs lost weight within minutes after molting. Moreover, high humidity rescued the lethality of molted dsLmABCH-9C-injected nymphs. In histological experiments, we find that the amounts of inner-cuticular lipids are reduced in nymphs with suppressed LmABCH-9C expression. These data together indicate that LmABCH-9C is needed for lipid-dependent desiccation resistance, paralleling the function of ABCH-9C in Tribolium castaneum. Hence, the function of this ABC transporter seems to be conserved across insect species ranging from hemimetabolous (L. migratoria) to holometabolous (T. castaneum) species. In addition, we find that cuticle inward impermeability is compromised in nymphs with reduced LmABCH-9C function. In summary, consistent with the model that cuticular lipids are necessary to prevent desiccation and penetration of xenobiotics in insects, we hypothesize that LmABCH-9C is involved in the construction of a lipid-based barrier at the surface of the cuticle especially after molting to protect the animal against uncontrolled water loss and entry. Susceptibility of this ABC transporter to RNAi-mediated knockdown designates it as an excellent target for RNAi-based insect pest control.
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