Transport of sugar from source to sink in plants

In order to meet increasing demands for energy and food as the world population grows, there is an urgent need to produce sustainable fuel and increase crop yield beyond existing yield potentials.  A better understanding of the mechanisms of fixed carbon allocation from photosynthetic tissues to non-photosynthetic ones is critical to achieving the goal of redirecting sugar flux to storage tissues. Sugar transporters are required to facilitate the carbon allocation or partitioning in multicellular organisms. We have characterized the SWEET family of sugar transporters, which are involved in different biological efflux processes: Arabidopsis AtSWEET11 and 12 export sucrose into the apoplasm from the phloem parenchyma cells prior to phloem loading. atsweet11;12 double mutant impairs sucrose export out of the leaf⁽¹⁾. Furthermore, SWEET13 is found to be an additional player in the process of sucrose efflux before phloem loading. We also demonstrated that AtSWEET11, 12 and 15 are required for seed filling. Triple mutant atsweet11;12;15 exhibits severely delayed embryo development and reduced seed yield⁽²⁾. However, overexpression expression of SWEETs leads to the unexpected results-stunted growth. Recently, the crystal structures from several SWEETs are available, which offers a valuable foundation for engineering sugar flux to increase crop yields and biofuel through the structure-guided functional study of SWEETs.

1.         LQ Chen et al., Science. 335, 207–11 (2012).

2.         LQ Chen et al., Plant Cell. 27, 607–619 (2015).

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