• DcTm1-X2 showed high expression level in the leg of Diaphorina citri. • The expression level of DcTm1-X2 was down-regulated in C Las-infection groups. • DcTm1-X2 has interaction with CS and VAT. • The mortality rate of D. citri increased after knockdown of DcTm1-X2. • The infection rate of C Las was up-regulated after knockdown of DcTm1-X2. The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, is the transmitting vector of Candidatus Liberibacter asiaticus (C Las), which causes citrus disease Huanglongbing (HLB). In recent years, control of HLB has been achieved by reducing the vector population. In the present study, we identified an isoform of D. citri tropomyosin (herein designated as DcTm1-X1). DcTm1-X1 was down-regulated in C Las-infected ACPs compared with uninfected ACPs. Bioinformatics analysis revealed that the full-length DcTm1-X1 is 2955 bp and encodes a protein of 284 amino acids with a deduced molecular weight of 32.15 kDa. Phylogenetic tree analysis suggested that DcTm1-X1 shares a high amino acid identity with its homolog in Acyrthosiphon pisum. Higher DcTm1-X1 expression levels were found in the leg of the psyllid by reverse transcription quantitative PCR (RT-qPCR). According to Blue Native PAGE analysis and mass spectrometric analysis, DcTm1-X1 interacts with citrate synthase (CS) and V-type proton ATPase subunit B-like (VAT). In addition, knockdown of DcTm1-X1 by RNA interference (RNAi) significantly increased the mortality rate of nymphs and the infection rate of C Las at different time points. Taken together, our results show that DcTm1-X1 might play an important role in response to C Las, but also lay a foundation for further research on the functions of DcTm1-X1. [ABSTRACT FROM AUTHOR]