Isolation of a citrus chitinase cDNA and characterization of its expression in response to elicitation of fruit pathogen resistance

Chitinases are well-known antifungal proteins and belong to the pathogenesis-related (PR) group of proteins. In the present study, we screened a Valencia orange flavedo cDNA expression library with an antibody raised against a purified Valencia basic chitinase polypeptide and isolated its corresponding cDNA. The Valencia flavedo chitinase cDNA, designated chi1, is 875 bp in length, with an open reading frame of 693 bp. The chi1 gene encodes a predicted polypeptide of 231 amino acids with a predicted molecular mass of 25.1 kDa and a pI of 9. 15. The CHI1 protein shares 60, 58, and 56 % identity with the basic chitinase proteins of rice, grape and maize, respectively. Southern blot analysis indicated that chi1 is present as a low-copy gene. RNA gel blot hybridizations revealed that chi1 gene expression was markedly induced by various treatments that induce fruit resistance against the green mould pathogen Penicillium digitatum (Pers.:Fr.) Sacc. These treatments included elicitation of fruit pathogen resistance by UV irradiation, hot water brushing, and application of β-aminobutyric acid (BABA) and Candida oleophila antagonist yeast cells.