Water retention is critical for physiological homeostasis and survival in terres-trial insects.While deposition of hydrocarbons on insect cuticles as a key measure for wa-ter conservation has been extensively investigated,we know little about other mechanisms for preventing water loss in insects.Here,we report two fatty acid synthetic genes that are independent of hydrocarbon production but crucial for water retention in the German cockroach Blattella germanica (L.).First,an integument enriched fatty acid elongase gene(BgElo1) was identified as a critical gene for desiccation resistance in B.germanica;how-ever,knockdown of BgElo1 surprisingly failed to cause a decline in cuticular lipids.In addition,RNA interference (RNAi)-knockdown of an upstream fatty acid synthase gene(BgFas3) showed a similar phenotype,and transmission electron microscopy analysis re-vealed that BgFas3-or BgElo1-RNAi did not affect cuticle architecture.Bodyweight loss test showed that repression of BgFas3 and BgElo1 significantly increased the weight loss rate,but the difference disappeared when the respiration was closed by freeze killing the cockroaches.A water immersion test was performed,and we found that BgFas3-and BgElo1-RNAi made it difficult for cockroaches to recover from drowning,which was supported by the upregulation of hypoxia-related genes after a 10-h recovery from drown-ing.Moreover,a dyeing assay with water-soluble Eosin Y showed that this was caused by the entry of water into the respiratory system.Our research suggests that BgFas3 and BgElo1 are required for both inward and outward waterproofing of the respiratory system.This study benefits the understanding of water retention mechanisms in insects.

Xiao-Jin Pei;Tian-Tian Bai;Zhan-Feng Zhang;Nan Chen;Sheng Li;Yong-Liang Fan;Tong-Xian Liu

State Key Laboratory of Crop Stress Biology for Arid Areas and Key Laboratory of Integrated Pest Management on Crops in Northwestern Loess Plateau,Ministry of Agriculture,Northwest A &F University,Yangling,Shaanxi,712100,China;Guangdong Provincial Key Laboratory of Insect Developmental Biology and Applied Technology and Institute of Insect Science and Technology,School of Life Sciences,South China Normal University,Guangzhou,510631,China

中国昆虫科学（英文版）

[1]Xiao-Jin Pei;Tian-Tian Bai;Zhan-Feng Zhang;Nan Chen;Sheng Li;Yong-Liang Fan;Tong-Xian Liu-.Two putative fatty acid synthetic genes of BgFas3 and BgElo1 are responsible for respiratory waterproofing in Blattella germanica)[J].中国昆虫科学（英文版）,2022(01):33-50

BgFas3,BgElo1,waterproofing,Blattella,germanica,cuticles,cockroach,Bodyweight,cockroaches,drown

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