Progress 09/01/08 to 08/31/11
Outputs
OUTPUTS: All plant growth and development is dependent upon the proper control of carbohydrate partitioning; however, we do not know how this process is regulated at the genetic and molecular levels. Using a multidisciplinary approach spanning molecular genetics, physiology and cell biology we are addressing this gap in our knowledge. We identified genes, termed the Tie-dyed (Tdy) loci, that when mutated result in the hyperaccumulation of carbohydrates within discrete regions of maize leaves. From previous characterizations, we proposed that these genes function as sugar or osmotic stress sensors to promote the export of sucrose from leaves. In addition to understanding the molecular functions of the Tdy genes, this proposal seeks to define the molecular functions of the Sucrose transporter1 (SUT1) gene of maize. Aim 1 will further characterize the Tdy1 expression and function in carbon partitioning. We performed RNA in situ hybridizations and determined that Tdy1 was specifically expressed in developing phloem cells. We also transiently expressed a TDY1 fusion protein to the yellow fluorescent protein (YFP) and localized the protein to the endoplasmic reticulum. To confirm the expression in vivo, we transformed a Tdy1::YFP translational fusion under the native promoter into maize. This construct has been assembled and delivered to the MU plant transformation core facility. Aim 2 proposes to characterize the contributions of SUT1 in maize to phloem function. Through expression, morphometric, physiological and biochemical investigations, we demonstrated that SUT1 has a critical function in importing sucrose into the phloem in maize leaves. Our results were the first demonstration of the importance of SUTs in phloem loading in grasses. Aim 3 proposes to characterize and clone Tdy2 and to map Tdy3. We cloned the Tdy2 gene by a combination of map-based and transposon-tagging cloning strategies. We verified we identified the correct gene by analyzing multiple, independent mutant alleles. We are currently characterizing the gene's expression. We completed our characterization of Tdy3. Because we found that the gene acts in an independent pathway from Tdy1 and Tdy2, we renamed Tdy3 as Psychedelic. PARTICIPANTS: David Braun, Project Director. During the granting period, the PD moved to accept a new position at the University of Missouri, where he will complete the research for the last year of the grant. Thomas Slewinski, graduate student. Tom completed his Ph.D. and graduated. He is currently a postdoctoral fellow working with Bob Turgeon at Cornell University. Frank Baker, postdoctoral fellow. Frank accepted a job as a science writing editor. Adam Stubert, undergraduate student. Adam is completing his last year of undergraduate studies and applying for admission to medical school. TARGET AUDIENCES: Results of supported research were presented in the form of talks and posters at national and international scientific conferences to maize geneticists and plant biologists, as well as to faculty, postdocs, graduate and undergraduate students at several universities. Additionally, the research findings were communicated to the larger scientific community in the form of publications. PROJECT MODIFICATIONS: The PD moved from Penn State to the University of Missouri. The final year of the grant will be completed at MU. A request to transfer the remaining funds on the grant will be prepared shortly and submitted to AFRI. Hence, I am submitting a final project report instead of an annual progress report.
Impacts
Our studies on the Tdy and Sut1 genes provide fundamental information on genes controlling carbohydrate partitioning in maize. Understanding how these genes regulate carbohydrate partitioning will have profound impacts on future efforts to modify the delivery of fixed carbon to roots, flowers and developing seeds, and hence improve crop yields. This knowledge will also have significant impacts on our ability to redirect carbon to the cell wall to increase cellulose deposition to improve biomass feedstocks for the production of biofuels.
Publications
- Thomas L. Slewinski, Anshu Garg, Gurmukh S. Johal and David M. Braun (2010) Maize SUT1 functions in phloem loading, Plant Signaling and Behavior, 5: 687-690
- Thomas L. Slewinski and David M. Braun (2010) The Psychedelic genes of maize redundantly promote carbohydrate export from leaves, Genetics, 185: 221-232
- Thomas L. Slewinski and David M. Braun (2010) Current perspectives on the regulation of whole-plant carbohydrate partitioning, Plant Science, 178: 341-349
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Progress 09/01/08 to 08/31/09
Outputs
OUTPUTS: All plant growth and development is dependent upon the proper control of carbohydrate partitioning; however, we do not know how this process is regulated at the genetic and molecular levels. Using a multidisciplinary approach spanning molecular genetics, physiology and cell biology we are addressing this gap in our knowledge. We identified genes, termed the Tie-dyed (Tdy) loci, that when mutated result in the hyperaccumulation of carbohydrates within discrete regions of maize leaves. From previous characterizations, we proposed that these genes function as sugar or osmotic stress sensors to promote the export of sucrose from leaves. In addition to understanding the molecular functions of the Tdy genes, this proposal seeks to define the molecular functions of the Sucrose transporter1 (SUT1) gene of maize. Aim 1 will further characterize the Tdy1 expression and function in carbon partitioning. We performed RNA in situ hybridizations and determined that Tdy1 was specifically expressed in developing phloem cells. We also transiently expressed a TDY1 fusion protein to the green fluorescent protein (GFP) and localized the protein to the endoplasmic reticulum. To confirm the expression in vivo, we are constructing stable maize transgenic plants expressing the Tdy1::GFP translational fusion under the native promoter. This construct has been assembled and will soon be transformed into plants. Aim 2 proposes to characterize the contributions of SUT1 in maize to phloem function. Through expression, morphometric, physiological and biochemical investigations, we demonstrated that SUT1 has a critical function in importing sucrose into the phloem in maize leaves. Our results were the first demonstration of the importance of SUTs in phloem loading in grasses. Aim 3 proposes to characterize and clone Tdy2 and to map Tdy3. We have map-based cloned the Tdy2 gene to a narrow interval containing approximately 35 genes. We are sequencing these genes from the mutant and progenitor backgrounds to determine which gene is responsible for the mutation. Additionally, we are screening through transposon mutant alleles to find the responsible gene. We successfully mapped and performed initial phenotypic characterizations of Tdy3. PARTICIPANTS: David Braun, PD, Thomas Slewinski, graduate student; Frank Baker, postdoctoral fellow; Adam Stubert, undergraduate researcher. TARGET AUDIENCES: Results of supported research were presented in the form of talks and posters to maize geneticists, plant biologists and faculty at several universities. PROJECT MODIFICATIONS: None
Impacts
Our studies on the Tdy and Sut1 genes provide fundamental information on genes controlling carbohydrate partitioning in maize. Understanding how these genes regulate carbohydrate partitioning will have profound impacts on future efforts to modify the delivery of fixed carbon to roots, flowers and developing seeds.
Publications
- Ma, Y., Slewinski, T.L., Baker, R.F., and Braun, D.M., 2009, Tie-dyed1 encodes a novel, phloem-expressed transmembrane protein that functions in carbohydrate partitioning. Plant Physiology 149: 181-194.
- Braun, D.M. and Slewinski, T.L, 2009, Genetic control of carbon partitioning in grasses: Roles of Sucrose Transporters and Tie-dyed loci in phloem loading. Plant Physiology 149: 71-81.
- Slewinski, T.L., Meeley, R.B., and Braun, D.M., 2009, Sucrose transporter1 functions in phloem loading in maize leaves. Journal of Experimental Botany 80: 881-892.
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