SUCROSE AS A SIGNAL MOLECULE IN ASSIMILATE PARTITIONING

Authors: CHIOU, TZYY-JEN - PLANT BIOLOGY UOFI URBANA; BUSH, DANIEL

Submitted to: Proceedings of the National Academy of Sciences (PNAS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Plants leaves capture light energy from the sun and transform that energy into a useful form in the process called photosynthesis. The primary product of photosynthesis is sucrose. Generally, 50 to 80 percent of the sucrose synthesized is transported from the leaf to supply organic nutrients to many of the edible parts of the plant such as fruits, grains, and tubers. This resource allocation process is called assimilating partitioning and alterations in this system are known to significantly affect crop productivity. We have discovered that sucrose plays a second vital role in assimilating partitioning by acting as a signal molecule that regulated the activity and gene expression of the transporter that mediates long-distance sucrose transport. This discovery represents a major breakthrough in our understanding of the processes that regulate assimilate partitioning and identifies that signaling pathway as an excellent target for using biotechnology to modify crop productivity.

Technical Abstract: The proton-sucrose symporter mediates the key transport step in the resource distribution system that allows many plants to function as multicellular organisms. In the results reported here, we identify sucrose as a signaling molecule in a new transduction pathway that leads to the dynamic regulation of the proton-sucrose symporter. Sucrose symporter activity declined in plasma membrane vesicles isolated from leaves fed exogenous sucrose via the xylem transpiration stream. Symporter activity dropped to 35-50 percent of water controls when feed 100 mM sucrose and to 20-25 percent of controls in 250 mM sucrose percent. In contrast, alanine symporter and glucose transporter activities did not change in response to sucrose treatments percent Decreased sucrose symporter activity was detectable after 8 hr percent. and reached a maximum by 24 hr percent. Kinetic analyses of transport activity showed a decrease in Vmax. RNA gel blot analysis revealed a decrease in symporter message levels, suggesting a drop in transcriptional activity or a decrease in mRNA stability percent. Control experiments showed that these observations were not the result of changing osmotic conditions percent. Significantly, equal molar concentrations of hexoses did not mimic the response, thus demonstrating that this is a sucrose-specific response pathway percent. Sucrose-dependent changes in the sucrose symporter were reversible, suggesting this sucrose-sensing pathway can be modulated by environmental sucrose concentrations percent. These results have important implications for our understanding of the regulatory pathways in assimilating partitioning.