Functional Analysis of Maize Genes for Sucrose Metabolism

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Sucrose is literally "the life-blood of plants" and moves from photosynthetic leaves to growing cells and tissues. The most rapidly growing organs are those that have a high capacity for sucrose metabolism.Sucrose and/or its metabolic products can also affect expression of many genes. Control of sucrose metabolism can thus have profound physiological and developmental consequences for the plant at multiple levels. There are only two known paths for sucrose cleavage, catalyzed by either invertases or the reversible sucrose synthase reaction, respectively. Dissection of the processes involved has been difficult due to multiple genes, diverse functions of their protein products, and sensitivity of the genes to environmental, metabolic, and developmental signals. New materials from our lab and elsewhere now put us in an excellent position to dissect roles and regulation of specific genes for sucrose metabolism in maize. The combination of mutants, physiology, and relevance of maize as a grain model make this an ideal species for this research project. The proposed studies involve analysis of i) "knock-out" mutants deficient in only one of the sucrose synthase genes (sus1), ii) a newly identified gene for a third sucrose synthase (Sus3), and iii) transgenic maize plants expressing an invertase gene (Ivr2-GUS) designed to generate a blue color when the gene is induced. We will use these tools in combination with specific developmental, genetic, and physiological perturbations made possible using distinctive features of the maize plant. The proposed work will provide a previously unavailable means of addressing the roles and regulation of genes for sucrose metabolism.