|Van Ekert, Evelien|
|Shatters, Robert - Bob|
|Rouge, Pierre - University Of Toulouse|
|Powell, Charles - University Of Florida|
|Smagghe, Guy - Ghent University|
|Borovsky, Dov - University Of Florida|
Submitted to: Science Magazine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/2015
Publication Date: N/A
Interpretive Summary: Citrus huanglongbing (HLB) disease has caused unprecedented damage to the citrus industry in the state of Florida and threatens citrus production in other states and globally. This bacterial disease is spread among citrus trees by an insect pest, the Asian citrus psyllid. To combat this threat, effective and sustainable alternatives to chemical pesticide application are being investigated for the control of this psyllid. Many such strategies focus on blocking specific biological processes in the insect pest. Research presented in this paper was performed to understand how psyllid development is controlled with the long-term objective being to transform this information into a new psyllid control strategy. One way insects control organism developmental is through the regulatory activity of a family of molecules called juvenile hormones (JHs). When synthesized and released, these molecules regulate many cellular processes involved in growth and development. Different forms of juvenile hormone function in different insects and different strategies are used by the organisms to synthesis the functional juvenile hormones. In this published work scientists at the USDA, ARS, U.S. Horticultural Research Laboratory in Fort Pierce, Florida identified an enzyme used in the biosynthesis of a functional juvenile hormone in the Asian citrus psyllid. This represents the first identification and characterization of this enzyme in any insect and identifies an important new target for the development of improved control strategies for the Asian citrus psyllid and a number of other pest insects.
Technical Abstract: The Asian citrus psyllid, Diaphorina citri, transmits a phloem-limited bacterium, Candidatus Liberibacter asiaticus that causes citrus greening disease. Because juvenile hormone (JH) plays an important role in adult and nymphal development, we studied the final steps in juvenile hormone biosynthesis in Diaphorina citri. A putative juvenile hormone acid methyltransferase ortholog gene (jmtD) and its cognate complimentary DNA were identified by searching Diaphorina citri genome database. Expression analysis shows expression in all life stages. In adults, it is expressed in the head-thorax, (containing the corpora allata), and the abdomen (containing ovaries and male accessory glands). A 3D protein model identified the catalytic groove with catalytically active amino acids and the S-adenosyl methionine (SAM)-binding loop. The complimentary DNA was expressed in Escherichia coli cells and the purified enzyme showed high preference for farnesoic acid (FA) and homo farnesoic acid (kcat of 0.752 x 10-3 and 0.217 x 10-3 s-1, respectively) as compared to juvenile hormone acid I (JHA I) (cis/trans/cis; 2Z,6E, 10cis), JHA III (2E, 6E, 10cis), and JHA I (trans/cis/cis; 2E,2Z, 10cis) (kcat of 0.081 x 10-3, 0.013 x 10-3, and 0.003 x 10-3 s-1, respectively). This suggests that this ortholog is a DcFA-o-methyl transferase gene (fmtD), not a jmtD, and that juvenile hornmone biosynthesis in Diaphorina citri proceeds from farnesoic acid to Juvenile hormone III through methyl farnesoate (MF). DcFA-o-MT does not require Ca2+, Mg2+ or Zn2+, however, Zn2+ (1 mM) completely inhibits the enzyme probably by binding H115 at the active groove. This represents the first purified FA-o-MT from Hemiptera with preferred biological activity for farnesoic acid and not juvenile hormone acid.