The control of maize northern leaf blight has always been an important problem in maize production, and understanding its pathogenic process is an important prerequisite for controlling the harm of maize northern leaf blight. The pathogenic process of maize bacterial leaf blight is the process of mutual recognition and interaction between maize bacterial leaf blight and host maize. Studying the signal transduction mechanism in this specific interaction process is of great significance for deeply understanding the pathogenic mechanism of maize leaf blight, designing new fungicides and proposing new plant disease control strategies. In this paper, the regulation of Ca2+ signal transduction pathway on the morphological structure and pathogenicity of conidia of maize leaf blight was studied. In this paper, the specific inhibitors of Ca2+ signal transduction pathway were used to determine the relationship between Ca2+ signal transduction pathway and spore germination, appressorium formation and pathogenicity of maize bacterial leaf blight. It was found that the inhibitory effects of calmodulin inhibitor TFP and calmodulin phosphatase inhibitor CsA on conidia germination and appressorium formation increased obviously with the increase of concentration. At the same concentration, the inhibitory effect of the inhibitor on the formation of appressorium is greater than that of spore germination, and the inhibitor can make appressorium obviously smaller or even unable to form. These results indicate that calcium signal transduction pathway is involved in the regulation of spore germination and appressorium formation of maize bacterial leaf blight under hydrophobic conditions. According to the conserved region of calmodulin amino acid sequence, degenerate primers were designed, and the homologous fragment of calmodulin gene was obtained by PCR technology, and the full-length cDNA sequence of calmodulin was obtained by SMART-RACE technology. According to the full-length cDNA sequence of CaM gene, gene-specific primers were designed to amplify the genomic DNA of Cercospora maydis, and the full-length DNA of CAM gene was obtained. The homology analysis between BLASTX software and the known proteins in GenBank showed that the amino acid sequence encoded by the open reading frame was 95% ~ 100% similar to the calmodulin gene of many fungi, such as rice blast fungus, wheat sheath blight fungus and rice blast fungus. Therefore, it is preliminarily speculated that the sequence is the calmodulin gene CaM of Cercospora maydis, and the obtained cDNA sequence has been submitted to GenBank (accession number: EF0 10936). Full-length DNA and cDNA of CaM gene of Xanthomonas oryzae PV. oryzae. Maydis is 776 BP and 450 bp, encoding 149 amino acids with 4 introns. All introns found in the experiment conform to GT-AG rules. The promoter sequence of CaM gene was obtained by genome walking technology, and the promoter sequence was analyzed by Proscan online software. It is found that the promoter sequence contains several conserved sequences related to transcription regulation (such as TATA-box, Sp 1, AP-2 and TFIID). Southern hybridization results showed that CaM gene of Xanthomonas campestris existed as a single copy in the genome. In order to study the regulatory effect of calmodulin gene on the pathogenicity of maize leaf blight, an antisense induced expression vector of maize leaf blight was constructed, and its correctness was verified by enzyme digestion. Using PEG-mediated transformation system, the constructed antisense expression vector containing hygromycin resistance screening marker was transformed into the protoplast of botrytis cinerea to obtain 14 resistant transformant, which can be continuously subcultured on hygromycin resistance plate. Two antisense expression mutants of CaM gene were obtained by using designed gene-specific primers and molecular hybridization technology. Under the condition of quinic acid induction, the conidia germination rate of the antisense expression mutant of CaM gene of Cercospora maydis decreased, and most of the attached cells formed after conidia germination were deformed, and the melanin deposition decreased, and the toxicity of the extracted HT- toxin to the leaves of susceptible hosts was significantly reduced. The calmodulin A subunit and calmodulin-dependent protein kinase gene downstream of calmodulin were cloned by candidate gene method. Calcineurin A subunit encodes 525 amino acids. The homology analysis between the encoded amino acid sequence and the known proteins in GenBank showed that the similarity between the encoded amino acid sequence and calcineurin genes of many fungi such as Sclerotinia sclerotiorum, Sclerotinia sclerotiorum and Botrytis cinerea was 860% ~ 94%. Therefore, it is preliminarily speculated that the sequence is the calcineurin gene CNA of Cercospora maydis, and the obtained cDNA sequence has been submitted to GenBank with accession number (EF407562). The gene contains six introns, namely 1 16bp, 47bp, 47bp, 47bp, 47bp and 49bp. There are four different subtypes of calmodulin-dependent protein kinases in maize northern leaf blight. Three calmodulin-dependent protein kinases have been cloned by RACE technology, and the fourth one only got a partial fragment. The obtained cDNA sequence has been submitted to GenBank with accession numbers (EU605885, EU605886, EU605887). Four different subtypes of calmodulin-dependent protein kinases all contain ATP binding sites and active site conserved motifs. Signal transduction pathway plays an important role in the construction of spore morphology and pathogenicity of maize leaf blight. The inhibition experiment and antisense inhibition experiment of calmodulin gene showed that calmodulin gene played an important role in the formation of normal adherent cells of maize leaf blight, and calmodulin also regulated the synthesis of toxin. Calmodulin-dependent phosphatase and kinase genes are important components of calcium signal transduction pathway of maize bacterial leaf blight, and their cloning laid a foundation for further understanding of calcium signal pathway of maize bacterial leaf blight.