GENOMIC AND BIOCHEMICAL ANALYSIS OF ONION (ALLIUM CEPA L.) SULFUR METABOLISM
The wide variation in onion bulb sulfur compounds associated with flavour and health attributes is well documented but poorly understood at the molecular level. We are using a combination of genomic, agronomic and biochemical methods to dissect key factors underlying this variation. EST sequencing and homology-based cloning have permitted identification of cDNAs for most structural genes in the pathway of sulfate assimilation. We have used these to develop markers for candidate gene mapping and measure gene expression at mRNA and protein level. Since earlier studies revealed significant differences in sulfur partitioning among onion varieties we compared the expression of the sulphur assimilation pathway in mild and pungent varieties to determine whether sulfur uptake and flavour intensity differences are associated with differential regulation of the pathway. Results confirmed that there are significant differences in gene expression and enzyme activity between varieties and significant changes on transition to bulbing. We have optimised gas chromatographic analysis of the lachrymatory factor thiopropanal-S-oxide as a direct measure of a flavour bioactive. Our experience in field-based agronomic and mapping studies has confirmed that this is a practical and economical way to profile flavour in large-scale genetic and agronomic studies.
McCallum, J., Pither-Joyce, M., Shaw, M., Porter, N., Searle, B., McManus, M. and Havey, M.J. (2005). GENOMIC AND BIOCHEMICAL ANALYSIS OF ONION (ALLIUM CEPA L.) SULFUR METABOLISM. Acta Hortic. 688, 75-84
onions, sulfur, gene mapping, gene expression, flavour