Journal of Experimental Botany, Vol. 54, No. 381, pp. 309-316,
January 2, 2003
© 2003 Oxford University Press
Malate synthase gene expression during fruit ripening of Cavendish banana (Musa acuminata cv. Williams)
Received 25 June 2002; Accepted 12 September 2002
Plant Genetic Engineering Laboratory, Department of Biological Sciences, Faculty of Science, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260, Republic of Singapore
1 To whom correspondence should be addressed. Fax: +65 6779 2486. E-mail: dbspuaec{at}nus.edu.sg
2 Present address: Department of Plant Biology, Cornell University, Ithaca, New York 14853, USA.
Malate synthase (MS) is a key enzyme responsible for malic acid synthesis in the glyoxylate cycle, which functions to convert stored lipids to carbohydrates, by catalysing the glyoxylate condensation reaction with acetyl-CoA in the peroxisome. In this study, the cloning of an MS cDNA, designated MaMS-1, from the banana fruit is reported. MaMS-1 was 1801 bp in length encoding a single polypeptide of 556 amino acid residues. Sequence analysis revealed that MaMS-1 possessed the conserved catalytic domain and a putative peroxisomal targeting signal SK(I/L) at the carboxyl terminal. MaMS-1 also shared an extensive sequence homology (79–81.3%) with other plant MS homologues. Southern analysis indicated that MS might be present as multiple members in the banana genome. In Northern analysis, MaMS-1 was expressed specifically in ripening fruit tissue and transcripts were not detected in other organs such as roots, pseudostem, leaves, ovary, male flower, and in fruit at different stages of development. However, the transcript abundance in fruit was affected by stage of ripening, during which transcript was barely detectable at the early stage of ripening (FG and TY), but the level increased markedly in MG and in other fruits at advanced ripening stages. Furthermore, MaMS-1 expression in FG fruit could be stimulated by treatment with 1 µl l–1 exogenous ethylene, but the stimulatory effect was abolished by the application of an ethylene inhibitor, norbornadiene. Results of this study clearly show that MS expression in banana fruit is temporally regulated during ripening and is ethylene-inducible.
Key words: Banana, ethylene, fruit ripening, gene expression, malate synthase, Musa acuminata.