A non-ACC pathway for ethylene biosynthesis in Botrytis cinerea

► Botrytis cinerea produced ethylene when grown on a medium with methionine or KMBA. ► As ACC did not stimulate ethylene production in B. cinerea it is not a precursor. ► AOA inhibited ethylene synthesis in B. cinerea, suggesting a role for a pyridoxal phosphate mediated enzyme. ► [U 14C] methionine was converted to 14C-ethylene with high efficiency in B. cinerea. ► The enzyme synthesising ethylene in B. cinerea is different from ACC oxidase in higher plants. Premature softening and tissue senescence occur in kiwifruit infected with Botrytis cinerea. While ethylene production is enhanced in infected fruit and B. cinerea produces ethylene on defined media in vitro the source of ethylene in this pathosystem is unclear. Ethylene production by B. cinerea was enhanced when methionine or ∝-keto-methylthiobutyric acid (KMBA) was added to a defined (modified Pratts) medium. Although 1-aminocyclopropane-1-carboxylic acid (ACC) did not stimulate ethylene production, ∝-aminooxyacetic acid (AOA) was inhibitory suggesting a role for a pyridoxal phosphate mediated enzyme reaction down stream from the methionine/KMBA stimulated ethylene biosynthetic pathway. Cobalt chloride (Co 2+) was inhibitory, but after a 4-d lag period ethylene production from B. cinerea cultures containing methionine and Co 2+ reached the same level as those without Co 2+. [U 14C] methionine was converted to 14C-ethylene with high efficiency indicating that it is a direct precursor, while [2,3 14C]-ACC did not yield radioactively labelled ethylene. These results suggest that the ethylene biosynthetic pathway in B. cinerea does not involve ACC as a precursor and that the enzyme responsible for synthesising ethylene is similar to, but different from, ACC oxidase from higher plants. The ethylene biosynthetic pathway in B. cinerea is yet to be determined.