Abstract: 【Objective】The objective of this study is to provide a basis for understanding the important role of lysozyme genes in Bemisia tabaci infected by the fungus Beauveria bassiana , identify lysozyme genes and analyze their sequence features, evolutionary relationships and expression pattern, and to provide a theoretical foundation for charifying innate immunity in B. tabaci. 【Method】Target genes were screened from the results of the second-generation high-throughput sequencing against the redundancy nucleotide databases when the E value ＜10^-5. The open reading frame and amino acid sequence of BtLyzs were found using the ORF Finder software; the protein domains of BtLyzs were predicted using Pfam and SMART software; the signal peptide sequence of BtLyzs was predicted using SignalP 4.1 Server; the amino acid sequence alignment of BtLyzs was performed using the MEGA6.0 software; BtLyzs were characterized by using phylogenetic analysis with homologous genes of 31 other insects, a neighbor-joining of phylogenetic tree was constructed using the MEGA 6.0 software for further analysis and identification of the genes. The expression pattern of screened genes were determined at egg, nymph and adult stages of B. tabaci which were infected by the fungus Be. bassiana after 12, 24, 36, 48, 60 h using the quantitative real-time PCR (qRT-PCR). 【Result】 Four lysozyme genes were identified and designated as BtLyz1, BtLyz2, BtLyz3 and BtLyz4, which were 1 819, 1 149, 829, 928 nt, respectively. They were predicted to encode proteins of 159, 160, 148, 160 amino acids, respectively. Amino acid sequence alignment, phylogenetic analysis and protein tertiary structure prediction showed that BtLyz1 and BtLyz4 belong to i-type lysozymes, BtLyz2 and BtLyz3 belong to c-type lysozymes. BtLyz-1 formed a clade specific with Acyrthosiphon pisum of ApLyz-i1, BtLyz4 formed a clade specific with Diaphorina citri of DcLyz-i3 and Acyrthosiphon pisum of ApLyz-i2; BtLyz2 and BtLyz3 formed a clade specific with Nilaparvata lugens of NlLyz-c1 and Harmonia axyridis of HaLyz-c3. Compared to the control, the relative expression of all four genes in egg and BtLyz4 in nymph were not induced significantly by fungi-infected; the transcription of BtLyz1 nymph stage underwent the fluctuation of up-regulation, down-regulation, and second up-regulation and peaked at 24 h, it was increased 4.55 folds compared to the control; the transcription of BtLyz1 and BtLyz4 adult stage underwent the fluctuation of up-regulation, down-regulation, and second up-regulation and peaked at 60 h, they were increased 11.31 and 4.21 folds compared to the control. The transcription of BtLyz2 and BtLyz3 nymph stage underwent the fluctuation of up-regulation and down-regulation and peaked at 24 h, they were increased 5.09 and 8.31 folds compared to the control, then down-regulated obviously at 60 h, they were reduced 0.19 and 0.13 folds compared to the control. The transcription of BtLyz2 and BtLyz3 adult stage underwent the fluctuation of up-regulation and down-regulation and peaked at 24 h, they were increased 5.56 and 8.84 folds compared to the control. 【Conclusion】 Four BtLyz genes were identified in B. tabaci. Among them, two are c-type and two are i-type lysozymes. Transcriptional levels of four BtLyzs genes in B. tabaci were induced through different developmental stages and different time points in fungi-treated individuals compared to the control, they were not induced significantly in eggs, and showed different expression trends in nymphs and adults. The four BtLyzs genes probably might participated in the innate immune responses to fungus infection, and could be a new potential target for biocontrol of B. tabaci.

Key words: Bemisia tabaci, lysozymes, bioinformatic analyses, quantitative real-time PCR