Candidate Salivary Effectors Screening Of Bemisia Tabaci Q And Its Resistance Monitoring To Spirotetramat In Five Field Strains Across China

Originated from tropics and subtropics,Bemisia tabaci is now disseminated over 100 areas and countries worldwidely by virtue of its gift in surviving.To sustain its development,B.tabaci utilizes its specialized mouthpart feeding phloem sap of its host plant for nutrition.As a consequence,B.tabaci not only directly consumes host nourishment,but also indirectly secretes honeydew causing sooty mould and propagates hundreds of virus leading to serious plant diseases,which all brings huge loss to world agriculture production.However,management of B.tabaci,for the present,mainly depends on simplex chemicals which resulted in resistance of B.tabaci to kinds of insecticides,and new pathways of B.tabaci control as well as new insecticides with novel mechanisms is desiderated.Complicated mechanisms of interaction between B.tabaci and host plant were long mysterious to scientists,while knowing these interaction mechanisms at a molecular level provides us a new path of B.tabaci management and in which salivary effectors play an important role;other insecticides with novel action mode like spirotetramat also bring hope to successful management of B.tabaci.The study was carried out from the two aspects above mentioned.Firstly,based on available database of B.tabaci,predictions of its salivary effectors were done and with a combination of sequence analysis,bioassays,transient expression and analysis of expression in specific tissues of B.tabaci,preliminary function analysis of B.tabaci candidate effectors.Secondly,resistance of five B.tabaci field populations to spirotetramat in China were monitored from 2015 to 2016.1.Prediction of Q B.tabaci candidate effectors.Based on the genome and transcriptome database of Q B.tabaci,this study predicted a series of candidate effectors utilizing two pipelines.One was taking advantage of genome database to rectify coding sequence?CDS?of the previously predicted salivary proteins according to published literatures and by prediction of signal peptide and transmembrane domain,finally 4 coding sequence were kept as candidates.The other was starting directly from the 13651 unigenes of the Q B.tabaci salivary gland transcriptome.And then through blast to the genome,195 candidates with a predicted signal peptide and without a transmembrane domain were kept as candidates.Along with characteristics of polymorphism within species and up-regulated expression when feeding,14 candidate effectors were furtherly retained.Therefore,this study has screened and kept 18 candidates in total.2.Cloning of candidate genes and preliminary function analysis.After work of prediction was done,candidate genes were then cloned and part of them were analyzed.Among the 18 candidates,16of them were successfully cloned and verified by sequencing.For function analysis,plant expression vectors were constructed and by experiment of transient expressions,6200,7722 and 11666 could induced Nicotiana Benthamiana defense response but cannot suppress PCD?programed cell death?response caused by Bax.And after over-expression of candidates,candidate 3 was found to decrease the fecundity of B.tabaci while candidate 1 could improve oviposition.Besides,by real-time fluorescent quantitative PCR of candidates,significant expression discrepancy within head and thorax part and abdomen part were found.3.Resistance monitoring of five B.tabaci field populations to spirotetramat.Five field populations from five areas in China were monitored for their resistance change to spirotetramat.As results showed,spirotetramat was much more toxic to larvae than eggs.And the LC₅₀ value of larvae from Hubei strain in 2016 was less than 5 mg/L while for eggs the value was more than 250 mg/L.Among the five areas,Hubei strains exhibited the highest resistance level to spirotetramat.Although spirotetramat was still of good control effects on B.tabaci larvae,the rapidly developed resistance could not be neglected and a mixed application of spirotetramat and other insecticides with novel action modes would be recommended to slow down the resistance development of B.tabaci.