The Ethylene Biosynthesis-Inducing Xylanase: Its Induction inTrichoderma virideand Certain Plant Pathogens

Abstract

A protein component of Cellulysin is known to induce ethylene biosynthesis in a variety of plant tissues and harbors an endo-beta-1,4-xylanase activity. Antiserum to the native ethylene biosynthesis-inducing xylanase immunoprecipitates both the enzymatic and biological activities. However, antisera raised against either the denatured 22- or 14-kilodalton (kDa) polypeptides comprising the native protein were ineffective in precipitating either activity. All three antibodies recognized the 14- and 22-kDa antigens on immunoblots. Synthesis of a single 22-kDa extracellular polypeptide detectable on immunoblots with the three antisera against the Cellulysin polypeptides was inducible in Trichoderma viride during growth on D-xylose, xylan, or crude cell-wall preparations. Induction was not observed when the fungus was grown on L-xylose, beta-methyl-D-xylose, glucose, or several purified cell-wall polymers, including pectin, polygalacturonate, arabinogalactan, and cellulose. Production of this protein was influenced by substrate concentration and culture pH. When grown in the induction medium, several other species of Trichoderma and Gliocladium also synthesize a 22-kDa xylanase that could be detected on immunoblots and was capable of inducing ethylene biosynthesis. Isoelectric focusing demonstrated that the cross-reactive polypeptides from these fungi exist as isoforms. The primary form had a pI of 9.4, and less abundant forms focused at pI 8.4 and lower. Culture filtrates of two plant pathogens, Fusarium oxysporum f. sp. pisi and Macrophomina phaseolina, also contained ethylene biosynthesis-inducing and xylanase activities, as well as a 22-kDa cross-reactive polypeptide. M. phaseolina filtrates also contained substantial amounts of a 14-kDa polypeptide similar to that found in Cellulysin