CHARACTERIZATION OF A GENE ENCODING CYANIDE HYDRATASE IN LEPTOSPHAERIA MACULANS, THE CAUSAL AGENT OF BLACKLEG DISEASE OF OILSEED BRASSICAS
AC SEXTON and BJ HOWLETT
School of Botany, University of Melbourne, Parkville 3052, Australia
Background and objectives
Results and conclusions
Cyanide hydratase in L. maculans is transcribed at a very low level in complete medium, at slightly higher levels in the presence of hydrolysis products of 2-propenyl glucosinolate (1.0 mM), and at extremely high levels after 4 h in the presence of potassium cyanide (0.1 and 1.0 mM), as shown by hybridization of the cDNA to an mRNA sized 1.1 kb. The cyanide hydratase mRNA was also detected during infection of Indian mustard cotyledons. Since cyanide hydratase transcription in L. maculans is inducible by 2-propenyl glucosinolate hydrolysis and much more strongly by potassium cyanide, this suggests that cyanide may be released during glucosinolate breakdown in Indian mustard. To test this we measured the amount of hydrogen cyanide released from macerated leaves of Indian mustard and canola, and from pure 2-propenyl glucosinolate hydrolysis. No cyanide was detected from pure 2-propenyl glucosinolate or from Indian mustard leaves, however a small amount (25 nmol/g fresh weight) was released from adult canola leaves. Canola has a high content of hydroxy aliphatic glucosinolates, which yield hydroxynitriles upon hydrolysis, and in other plants hydroxynitriles are known to breakdown into hydrogen cyanide. Therefore L. maculans may need to detoxify cyanide during infection of canola. Further work will involve testing whether the cyanide hydratase gene is expressed during infection of adult canola and Indian mustard plants, and disrupting the gene to test whether a lack of cyanide hydratase causes any reduction in fungal virulence.