Holford, Paul

AbstractThe severe Asiatic form of huanglongbing (HLB), caused by “Candidatus Liberibacter asiaticus” (CLas), threatens global citrus production via the citrus psyllid, Diaphorina citri. Culturing challenges of CLas necessitate reducing D. citri populations for disease management. CLas boosts the fecundity of CLas‐positive (CLas+) D. citri and fosters its own proliferation by modulating the insect host's juvenile hormone (JH), but the intricate endocrine regulatory mechanisms remain elusive. Here, it is reported that the D. citri ecdysis‐triggering hormone (DcETH) and its receptor DcETHR play pivotal roles in the reciprocal benefits between CLas and D. citri within the ovaries, influencing energy metabolism and reproductive development in host insects; miR‐210, negatively regulates DcETHR expression, contributing to this symbiotic interaction. CLas infection reduces 20‐hydroxyecdysone (20E) levels and stimulates DcETH release, elevating JH production via DcETHR, enhancing fecundity and CLas proliferation. Furthermore, circulating JH levels suppress 20E production in CLas+ ovaries. Collectively, the orchestrated functional interplay involving 20E, ETH, and JH increases energy metabolism and promotes the fecundity of CLas+ D. citri and CLas proliferation. These insights not only broaden the knowledge of how plant pathogens manipulate the reproductive behavior of insect hosts but also offer novel targets and strategies for combatting HLB and D. citri.

The phloem-limited bacterium ‘Candidatus Liberibacter asiaticus’ (CLas) is the putative causal pathogen of the severe Asiatic form of huanglongbing (citrus greening) and is most commonly transmitted by the Asiatic citrus psyllid Diaphorina citri. CLas severely affects many Citrus species and hybrids and has been recorded in the Citrus relative, orange jasmine, Murraya paniculata (L.) Jack (syn. M. exotica L.). In this study, 13 accessions of three Murraya species (M. paniculata, M. sumatrana Roxb., and M. lucida [G.Forst.] Mabb.) and the Papuan form of a putative hybrid (M. omphalocarpa Hayata) were identified morphologically and molecularly based on sequence identity of the matK-5′trnK region of the chloroplast genome, and infection on these plants under field conditions was determined by PCR and quantitative real-time PCR (qPCR) on two to four occasions over 14 months. CLas was repeatedly detected in leaflet midribs by PCR and qPCR on four and three accessions of M. paniculata and M. sumatrana, respectively. It was not detected in leaflet midribs of single accessions of M. lucida and M. omphalocarpa. The species identification of the CLas-positive accessions was further confirmed using all the molecular taxonomic markers consisting of the six fragments of the maternally inherited chloroplast genome and part of the nuclear-encoded internal transcribed spacer (ITS) region. The results indicated that natural infection of M. paniculata and M. sumatrana with CLas can occur in Java. To our knowledge, this is the first demonstration of the natural infection of M. sumatrana with CLas. Further studies are required to determine whether infections persist in the absence of D. citri.

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

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

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

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

AbstractThe evolution of insect vector‐pathogen relationships has long been of interest in the field of molecular ecology. One system of special relevance, due to its economic impacts, is that between Diaphorina citri and ‘Candidatus Liberibacter asiaticus’ (CLas), the cause of the severe Asian form of huanglongbing. CLas‐positive D. citri are more fecund than their CLas‐negative counterparts, boosting opportunities for pathogens to acquire new vector hosts. The molecular mechanism behind this life‐history shift remains unclear. Here, we found that CLas promoted ovarian development and increased the expression of the vitellogenin receptor (DcVgR) in ovaries. DcVgR RNAi significantly decreased fecundity and CLas titer in ovaries, extended the preoviposition period, shortened the oviposition period and blocked ovarian development. Given their importance in gene regulation, we explored the role of miRNAs in shaping these phenotypes and their molecular triggers. Our results showed that one miRNA, miR‐275, suppressed DcVgR expression by binding to its 3' UTR. Overexpression of miR‐275 knocked down DcVgR expression and CLas titer in ovaries, causing reproductive defects that mimicked DcVgR knockdown phenotypes. We focused, further, on roles of the Juvenile Hormone (JH) pathway in shaping the observed fecundity phenotype, given its known impacts on ovarian development. After CLas infection, this pathway was upregulated, thereby increasing DcVgR expression. From these combined results, we conclude that CLas hijacks the JH signalling pathway and miR‐275, thereby targeting DcVgR to increase D. citri fecundity. These changes simultaneously increase CLas replication, suggesting a pathogen‐vector host mutualism, or a seemingly helpful, but cryptically costly life‐history manipulation.

AbstractDiaphorina citriis the primary vector of the bacterium, ‘CandidatusLiberibacter asiaticus’ (CLas) associated with the severe Asian form of huanglongbing.CLas-positiveD. citriare more fecund than theirCLas-negative counterparts and require extra energy expenditure. Therefore, understanding the molecular mechanisms linking metabolism and reproduction is of particular importance. In this present study, we found adipokinetic hormone (DcAKH) and its receptor (DcAKHR) were essential for increased lipid metabolism and fecundity in response toCLas infection inD. citri.Knockdown ofDcAKHandDcAKHRnot only resulted in triacylglycerol accumulation and a decline of glycogen, but also significantly decreased fecundity andCLas titer in ovaries. Combinedin vivoandin vitroexperiments showed that miR-34 suppressesDcAKHRexpression by binding to its 3’ untranslated region, whilst overexpression of miR-34 resulted in a decline ofDcAKHRexpression andCLas titer in ovaries and caused defects that mimickedDcAKHRknockdown phenotypes. In addition, knockdown ofDcAKHandDcAKHRsignificantly reduced juvenile hormone (JH) titer and JH signaling pathway genes in fat bodies and ovaries, including the JH receptor,methoprene-tolerant(DcMet), and the transcription factor,Krüppel homolog 1 (DcKr-h1), that acts downstream of it, as well as the egg development related genesvitellogenin 1-like(DcVg-1-like),vitellogenin A1-like(DcVg-A1-like) and the vitellogenin receptor (DcVgR). As a result,CLas hijacks AKH/AKHR-miR-34-JH signaling to improveD. citrilipid metabolism and fecundity, while simultaneously increasing the replication ofCLas, suggesting a mutualistic interaction inD. citriovaries withCLas.