Adipokinetic hormone signaling mediates the enhanced fecundity of <i>Diaphorina citri</i> infected by '<i>Candidatus</i> Liberibacter asiaticus'.

Abstract

<i>Diaphorina citri</i> serves as the primary vector for '<i>Candidatus</i> Liberibacter asiaticus (<i>C</i>Las),' the bacterium associated with the severe Asian form of huanglongbing. <i>C</i>Las-positive <i>D. citri</i> are more fecund than their <i>C</i>Las-negative counterparts and require extra energy expenditure. Therefore, understanding the molecular mechanisms linking metabolism and reproduction is of particular importance. In this study, we found adipokinetic hormone (<i>DcAKH</i>) and its receptor (<i>DcAKHR</i>) were essential for increasing lipid metabolism and fecundity in response to <i>C</i>Las infection in <i>D. citri</i>. Knockdown of <i>DcAKH</i> and <i>DcAKHR</i> not only resulted in the accumulation of triacylglycerol and a decline of glycogen, but also significantly decreased fecundity and <i>C</i>Las titer in ovaries. Combined in vivo and in vitro experiments showed that miR-34 suppresses <i>DcAKHR</i> expression by binding to its 3' untranslated region, whilst overexpression of miR-34 resulted in a decline of <i>DcAKHR</i> expression and <i>C</i>Las titer in ovaries and caused defects that mimicked <i>DcAKHR</i> knockdown phenotypes. Additionally, knockdown of <i>DcAKH</i> and <i>DcAKHR</i> significantly reduced juvenile hormone (JH) titer and JH signaling pathway genes in fat bodies and ovaries, including the JH receptor, <i>methoprene-tolerant</i> (<i>DcMet</i>), and the transcription factor, <i>Krüppel homolog 1 (DcKr-h1</i>), that acts downstream of it, as well as the egg development related genes <i>vitellogenin 1-like</i> (<i>DcVg-1-like</i>), <i>vitellogenin A1-like</i> (<i>DcVg-A1-like</i>) and the vitellogenin receptor (<i>DcVgR</i>). As a result, <i>C</i>Las hijacks AKH/AKHR-miR-34-JH signaling to improve <i>D. citri</i> lipid metabolism and fecundity, while simultaneously increasing the replication of <i>C</i>Las, suggesting a mutualistic interaction between <i>C</i>Las and <i>D. citri</i> ovaries.