SWEETs: Mechanistic model of sucrose allocation in grains of barley and rice

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Sucrose is the main source of carbon for growth and storage product synthesis in seeds. Our previous project identified HvSWEET11b and HvSWEET15a genes as key candidates for sucrose release in developing barley grains. We also verified their sucrose transport activity in vitro and localized their expression along the main sucrose allocation route. Now, we have generated transgenic barley plants with up and down regulated expression of SWEET genes, and plan their comprehensive characterization using our unique analytical (imaging) pipeline. We will apply magnetic resonance imaging (for surveying and monitoring of sucrose allocation in the living grain), infrared-based microspectroscopy (for high resolution quantitative sucrose mapping), RNASequencing, metabolite profiling and others for the analysis of developing grains. Moreover, concurrent molecular studies on rice revealed that OsSWEET11-1 and OsSWEET15-1 show all the hallmarks of being essential for grain filling in rice. Respective single and double mutant plants became available, and will also be analysed in the proposed project. This comparative analysis will solve the long-standing debate whether barley and rice exploit similar or distinct sucrose delivery routes. The project will exploit new genetic resources to study the genetic diversity in SWEET genes in genome wide association scans. Ultimately, a mechanistic view on sucrose import in grains of two important cereal crops will be provided as well as a knowledge base required for engineering of improved grain filling in cereals.