|DE Los Reyes, Benildo - UNIVERSITY OF ARKANSAS|
|MCGRATH, J MITCHELL|
Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 16, 2002
Publication Date: June 1, 2003
Citation: DE LOS REYES, B.G., MCGRATH, J.M. CULTIVAR-SPECIFIC SEEDLING VIGOR AND EXPRESSION OF A PUTATIVE OXALATE OXIDASE GERMIN-LIKE PROTEIN IN SUGAR BEET (BETA VULGARIS L.). JOURNAL OF THEORETICAL AND APPLIED GENETICS. 2003. v. 107(1). p. 54-61. Interpretive Summary: Field emergence and stand establishment of sugar beet is a long-standing problem for growers, because on average, 60% of the planted seed contributes to the maximum stand, and stand counts diminish during the growing season. The first eight weeks after emergence are critical to the beet's life. Improved early season seedling growth would have an economic impact by reducing the amount of seed planted to obtain adequate stands, as well as avoiding catastrophic stand failures that are costly to replant. To date, no method to select for early season seedling vigor has been available. We have developed a simple method to predict relative field emergence for varieties and seedlots. Using this method, we examined gene expression during germination in two varieties, one with high emergence and one with low emergence. We found that the high emerging variety produced an enzyme during stress that was not expressed in the low emerger. This germination specific enzyme (germin) produces hydrogen peroxide, which when added to germinating sugar beet seeds, stimulates germination. Hydrogen peroxide at low concentrations has been shown to induce expression of other stress-related genes. For the first time, a promising approach to selecting sugar beet for improved emergence is available. The impact of this work is that breeders can now select for enhanced emergence, leading to a lower cost of production for sugar beet growers.
Technical Abstract: Field emergence of sugar beet (Beta vulgaris) is an annual concern for growers, and improving emergence potential has not been amenable to selection due to developmental and environmental influences on seed quality. For genetic screening and breeding purposes, an in vitro germination system that reflects relative, field emergence potential was used to screen for germination-enhancing and stress-induced genes from germinating seedlings from two varieties. Three full-length germin-like protein (GLP) gene classes were recovered from stress-germinated seedlings of a superior emerging variety. GLP gene expression, oxalate oxidase protein activity, H2O2 content of stressed seedlings, but not catalase activity, were induced by stress germination conditions (e.g. excess water, NaCl, mannitol, or oxalate) in a good emerging hybrid, and were not induced in a poor emerging variety. Only one of the three germin-like protein genes (BvGer165) was differentially regulated, and was induced only in the good emerger. Hydrogen peroxide promoted germination and partially compensated solute-depressed germination percentages. Unlike other solute recovery by hydrogen peroxide regimes, recovery in oxalic acid plus H2O2 was cultivar-independent. A block in oxalate metabolism is postulated to contribute to lower germination under stress in the low emerging variety. Selection for stress-induced germin expression, or for down-stream targets, presents the first direct target to enable breeding for improved field emergence of sugar beet.