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INVESTIGATOR: Slewinski, T.

PERFORMING INSTITUTION:
CORNELL UNIVERSITY
ITHACA, NEW YORK 14853

ROLE OF PHLOEM LOADING ON GROWTH RATES IN POPLAR

NON-TECHNICAL SUMMARY: Commodities production from trees represents a significant portion of agricultural, manufacturing and energy business in the United States. Despite the critical importance of tree-based products in our daily lives, very little is known about the underlying physiology and genetics that govern the growth and resource allocation traits important for agricultural production. Phloem loading and transport plays a critical function in carbon allocation throughout the plant. Recent evidence indicates that phloem loading in poplar, and in many other tree species, is passive and therefore is not regulated by sucrose transporters. Rather, we propose that the synthesis of raffinose-family oligosaccharides (RFOs) plays an important regulatory role. The primary aim of this investigation is to determine the roles of RFOs in phloem loading and carbon transport in poplar (Populus trichocarpa), an important biofuels crop. By doing so, we test a new mechanistic model for passive phloem loading and the hypothesis that upregulating RFO synthesis in the phloem will increase growth rate and biomass accumulation. Therefore, results of this study could directly impact biofuels production. This is a fundamental research project that will advance our understanding of basic plant biology and has the potential for broad application in the renewable biofuels industry. This project will also advance the scientific, technical, and professional training of the postdoctoral fellow Dr. Thomas L. Slewinski.

OBJECTIVES: Goals: To determine the specific role of raffinose family oligosaccharides in phloem loading in poplar. Specific Hypotheses and Objectives: 1) RFO synthesis plays an important and previously unrecognized role in phloem transport in poplar. 2) More specifically, downregulation of RFO synthesis will severely inhibit phloem loading in poplar leading to reduced photosynthesis and growth rates. 3) Upregulating RFO synthesis in the phloem of poplar will stimulate photosynthesis by reducing mesophyll sucrose concentrations and will also increase carbohydrate transport to growing leaves. Increasing new leaf surface area will have an additional stimulatory effect, leading to substantially higher growth rates. 4) Facilitated export in poplar by upregulation of RFO synthesis will allow plants to take better advantage of additional photosynthate in high CO2 atmospheres. (This hypothesis is long-term and will not be addressed during the grant period.) By testing this new model of phloem loading, we could potentially increase the photosynthetic, growth, and biomass accumulation rates in poplar, which is an important biofuels crop.