Catabolism of l -methionine in the formation of sulfur and other volatiles in melon (Cucumis melo L.) fruit

Itay Gonda, Shery Lev, Einat Bar, Noga Sikron, Vitaly Portnoy, Rachel Davidovich-Rikanati, Joseph Burger, Arthur A. Schaffer, Ya'Akov Tadmor, James J. Giovannonni, Mingyun Huang, Zhangjun Fei, Nurit Katzir, Aaron Fait, Efraim Lewinsohn

Research output: Contribution to journalArticlepeer-review

60 Scopus citations

Abstract

Sulfur-containing aroma volatiles are important contributors to the distinctive aroma of melon and other fruits. Melon cultivars and accessions differ in the content of sulfur-containing and other volatiles. l-methionine has been postulated to serve as a precursor of these volatiles. Incubation of melon fruit cubes with 13C- and 2H-labeled l-methionine revealed two distinct catabolic routes into volatiles. One route apparently involves the action of an l-methionine aminotransferase and preserves the main carbon skeleton of l-methionine. The second route apparently involves the action of an l-methionine-γ-lyase activity, releasing methanethiol, a backbone for formation of thiol-derived aroma volatiles. Exogenous l-methionine also generated non-sulfur volatiles by further metabolism of α-ketobutyrate, a product of l-methionine-γ-lyase activity. α-Ketobutyrate was further metabolized into l-isoleucine and other important melon volatiles, including non-sulfur branched and straight-chain esters. Cell-free extracts derived from ripe melon fruit exhibited l-methionine-γ-lyase enzymatic activity. A melon gene (CmMGL) ectopically expressed in Escherichia coli, was shown to encode a protein possessing l-methionine-γ-lyase enzymatic activity. Expression of CmMGL was relatively low in early stages of melon fruit development, but increased in the flesh of ripe fruits, depending on the cultivar tested. Moreover, the levels of expression of CmMGL in recombinant inbred lines co-segregated with the levels of sulfur-containing aroma volatiles enriched with +1 m/z unit and postulated to be produced via this route. Our results indicate that l-methionine is a precursor of both sulfur and non-sulfur aroma volatiles in melon fruit.

Original languageEnglish
Pages (from-to)458-472
Number of pages15
JournalPlant Journal
Volume74
Issue number3
DOIs
StatePublished - 1 May 2013

Keywords

  • Cucumis melo
  • aroma compounds
  • l -methionine
  • melon fruit
  • methionine γ-lyase
  • stable isotope feeding
  • sulfur volatiles

ASJC Scopus subject areas

  • Genetics
  • Plant Science
  • Cell Biology

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