Abstract: Callose deposition is a common plant defense response to invasive pathogens and involved in plant innate immunity. In order to explore the expression of callose synthase（CalS）in citrus and the response to Huanglongbing（HLB），12 members of callose synthase genes（CsCalSs）were screened from the sweet orange（Citrus sinensis）genome and analyzed with bioinformatic tools. The coding amino acid sequences of these CsCalS genes showed high homology with callose synthase gene in Arabidopsis thaliana. The results produced by real time PCR revealed that the expression of CsCalS5 and CsCalS12 in citrus leaves were higher than that of other callose synthase genes. On the other hand，CsCalS5，CsCalS7 and CsCalS8 were all up-regulated in HLB-affected‘Shatangju’（C. reticulata）and‘Chandler’pummelo（C. grandis）comparing with the healthy control，indicated they may be involved in the response of citrus to the HLB pathogen.

Key words: citrus, Huanglongbing, callose synthase, gene；expression analysis