Co-ordinated regulation of chitinase and β-1,3-glucanase in bean leaves

Ethylene induced chitinase (EC 3.2.1.14) and β-1,3-glucanase (EC 3.2.1.29) to a similar extent in primary leaves of bean seedlings (Phaseolus vulgaris cv. Saxa). Both enzymes were purified from ethylene-treated leaves, and monospecific antibodies were raised aginst them. Ethylene treatments strongly increased the amount of immunore-active chitinase and β-1,3-glucanase. Ethylene enhanced synthesis of chitinase in vivo, as tested by immunoprecipitation after pulse-labelling with [(35)S]methionine. RNA was isolated from bean leaves and translated in a rabbit reticulocyte lysate system in vitro. The chitinase and the β-1,3-glucanase antiserum each precipitated a single polypeptide from the translation products. The precipitated polypeptides were 1500 and 4000 daltons larger, respectively, than native chitinase and native β-1,3-glucanase, indicating that the two enzymes were synthesized as precursors in vitro. The translatable mRNAs for both enzymes increased at least tenfold within 2 h in response to a treatment with ethylene. When ethylene was withdrawn after 8 h of incubation, the translatable mRNAs for both enzymes decreased somewhat more slowly, reaching the basal level about 25 h later. In all cases, there was a close correlation between the levels of translatable mRNA for chitinase and β-1,3-glucanase. A putative β-1,3-glucanase cDNA clone, pCH16, was isolated by hybrid-selected translation. The amount of β-1,3-glucanase mRNA, as measured by RNA blot analysis using pCH16 as a probe, increased rapidly in response to ethylene and decreased again after withdrawal of ethylene, indicating that the amount of hybridizable RNA and of translatable mRNA for β-1,3-glucanase were correlated. In conclusion, the results indicate that chitinase and β-1,3-glucanase are regulated co-ordinately at the level of mRNA.