Mechanisms of Gene Regulation
Martinez, Martha , Ortega, Jose Luis , Aleman, Lorenzo , Sengupta-Gopalan, Champa .
Understanding the function and regulatory mechanism of sucrose phosphate synthase in alfalfa nodules.
Alfalfa and other legumes form specialized root nodules that harbor symbiotic bacteria, Rhizobia, able to fix atmospheric nitrogen which the plant assimilates into glutamine. In exchange, the plant provides the bacteria with phloem-supplied and photosynthesis-derived sucrose for growth and energy production. Sucrose is synthesized by the enzymes sucrose phosphate synthase (SPS) and sucrose phosphatase (SPP) via the intermediate sucrose 6-phosphate and is broken down by the enzyme Sucrose synthase (SuSy). SPS can be regulated transcriptionally and posttranslationally by covalent modification via reversible phosphorylation and allosteric regulation via metabolites, Glc-6-P and phosphate. We have identified and isolated cDNA clones for at least two SPS families (SPSA and SPSB) that are differentially expressed. SPSA is predominantly expressed in root nodules, while SPSB is almost exclusively expressed in the leaves. The nodules exhibited many fold higher level of SPS activity compared to the leaves and the activity appeared to be higher in the night than during mid day. Our data also showed that there is an inverse correlation between the N levels and the SPS transcript level in both the leaves and the nodules. Experiments are in progress to localize the SPS transcripts in the nodules at a cellular level and to relate its expression with the functional roles of the cells where they are expressed. Knowing the metabolic state with regards to N and C under which the genes are induced will allow us to understand the regulatory trigger for its expression. If the site of expression of the SPS gene coincides with that of SuSy, we can conclude that SPS and SuSy are parts of the cycle to maintain optimal levels of sucrose, hexoses and starch in the nodules.
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1 - New Mexico State University, Molecular Biology and Plant and Environmental Sciences, Skeen Hall: Room 127N, Las Cruces, NM, 88003, Dona Ana
2 - New Mexico State University, Plant and Environmental Sciences
3 - New Mexico State University, Molecular Biology
4 - New Mexico State University, Molecular Biology and Plant and Environmental Sciences
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM