Purification and Characterization of an Antifungal Chitinase from Arabidopsis thaliana

Plants exhibit an altered pattern of protein synthesis in response to pathogen invasion and abiotic stress. One of these ;pathogenesis-related' proteins has been identified as chitinase, which is capable of inhibiting fungal growth in vitro. This observation has led to the suggestion that the in vivo role of chitinases is to protect plants against fungal invasion. Here, we report the purification and characterization of a basic chitinase from Arabidopsis thaliana (L.) Heynh. Columbia wild type. The purified enzyme has a molecular mass of approximately 32 kilodaltons as determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, and an apparent pl of approximately 8.7 as determined by isoelectric focusing. The purified protein is an effective inhibitor of the growth of Trichoderma reesei in vitro but does not affect the growth of several other fungi. Amino acid composition analysis of the intact protein as well as amino acid composition analysis and automatic Edman degradation of isolated tryptic fragments of the enzyme indicate that it may be identical to the product of a chitinase gene isolated from an Arabidopsis genomic library (Samac DA, Hironaka CM, Yallaly PE, Shah DM [1990] Plant Physiol 93: 907-914).