Increasing Rice Yield Via Leaf Starch Specific Transcription Factors.

Starch is an important contributor to plant growth as excess photosynthate is stored in leaves as starch during the day to be remobilized at night to support plant growth, and is the principal constituent of cereal seeds causing it to greatly influence crop yields.  Leaf starch is regulated in part by ADP-glucose pyrophosphorylase (AGPase), the rate limiting step of starch biosynthesis.   Transgenic rice with increased leaf AGP activity and plant biomass was subjected to RNA-sequencing.   The results indicate that the AGP transgene which increased leaf starch also caused the upregulation of several transcription factors (TFs).   The current study examines the potential of increasing starch biosynthesis in leaves via leaf-specific upregulation of selected TFs responsive to leaf starch levels.   Five TFs were chosen and used to create transgenic rice with leaf specific TF overexpression.    The preliminary results indicate that overexpression of three of the TFs significantly increase leaf starch.    This study will examine whole plant growth, photosynthesis, and gene expression in lines homozygous positive or negative for the presence of these three transcription factors.  We hypothesize that starch biosynthesis and plant biomass will be increased to a greater extent than with AGP overexpression alone since the TFs used should result in broad upregulation of carbohydrate metabolism.   Ultimately this project hopes to increase knowledge of the biological factors limiting plant growth associated with leaf starch biosynthesis, identify key TFs mediating the process, and increase plant productivity and agronomic yield.