|DE LOS REYES, BENILDO|
Submitted to: Molecular Genetics and Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2003
Publication Date: 8/1/2003
Citation: De Los Reyes, B.G., Myers, S.J., McGrath, J.M. 2003. Differential stress-induction of glyoxylate enzymes as a marker of seedling vigour in sugar beet (Beta vulgaris). Molecular Genetics and Genomics. 269(5):682-698.
Interpretive Summary: Growth of the sugar beet crop is most critical during the first eight weeks after planting. Varieties with high seedling vigor would be expected to alleviate grower concerns about emergence and stand establishment and result in more uniform stands, which ultimately optimizes harvest and sucrose recovery at the factory. Varieties differ in seedling vigor, but the precise mechanisms have not been deduced. We used high and low vigor sugar beet commercial hybrids, to show that genes and enzymes in the glyoxylate pathway, which is involved in using stored oils and fats in germinating seedlings, are highly expressed under stress in the high but not the low emerging hybrid. This is the first report that sugar beet uses this pathway, and this process has been unappreciated until now. The impact of these findings will be that sugar beet breeders will be able to select for varieties that use this important source of energy during germination, and result in varieties with enhanced emergence for growers.
Technical Abstract: Significant differences in seedling vigour exist among sugar beet (Beta vulgaris) hybrids. The seedling vigour trait likely is complex but efficient mobilization of seed storage reserves during germination and early seedling growth and in diverse environments must be considered. The involvement of lipid metabolism during germination of sugar beet under stress conditions was suggested by a high frequency of Expressed Sequence Tags (ESTs) with high similarity to isocitrate lyase (EC 22.214.171.124). Involvement of this glyoxylate enzyme during germination and seedling emergence was deduced from nucleotide sequencing of a subtracted cDNA library constructed from a good emerging sugar beet hybrid during stress germination. Under stress, genes involved in carbohydrate and lipid catabolism were differentially expressed in a vigorously emerging hybrid relative to a weakly emerging hybrid. Submergence and salinity stresses reduced the expression of an X-amylase gene in the weakly emerging hybrid. The vigorously emerging hybrid exhibited only a moderate reduction in X-amylase gene expression under the same conditions. The vigorously emerging hybrid showed increases in the expression of genes involved in lipid metabolism, particularly glyoxylate cycle enzymes, isocitrate lyase and malate synthase. The slower rate of carbohydrate catabolism under stress condition in the more vigorous emerging hybrid may be compensated by the enhancement of lipid catabolism and carbon utilization via anapleurotic reactions in the glyoxylate cycle. Differential activity of the glyoxylate cycle is a potential physiological marker to differentiate between high- and low-vigour sugar beet cultivars, and suggests a biochemical target for selection for enhanced germination and improved emergence in sugar beet.