HAVING A DENSELY PATTERNED VASCULATURE IS CRITICAL FOR THE FUNCTION OF A TYPE OF EFFICIENT PHOTOSYNTHESIS CALLED C4. INDEED, MANY C4 PLANTS SUCH AS SORGHUM AND MAIZE ARE MORE HIGHLY VASCULARIZED THAN THEIR C3 COUNTERPARTS, INCLUDING RICE AND BARLEY. DESPITE THE CRITICAL IMPORTANCE OF HAVING HIGH DENSITY VASCULATURE IN C4 PLANTS, VIRTUALLY NOTHING IS KNOWN ABOUT HOW IT IS ACHIEVED. THE MAJOR GOAL OF THIS PROJECT IS TO UNDERSTAND HOW VASCULAR PATTERNING OCCURS IN C4 GRASS CROPS, AND TO TRY TO USE THIS KNOWLEDGE TO INCREASE VASCULARIZATION OF C3 CROP PLANTS AND IMPROVE THEIR AGRONOMIC QUALITIES. TO ADDRESS THIS, WE WILL USE A SYSTEM WE DEVELOPED BASED ON A PAIR OF FUNCTIONALLY REDUNDANT DUPLICATED TRANSCRIPTION FACTORS, BLH12 AND BLH14, KNOWN TO PLAY ROLES IN VASCULAR PATTERNING OF MAIZE. BLH12/14 DOUBLE MUTANTS ABOLISH INTERMEDIATE VEIN INITIATION IN LEAVES AND CAUSE PREMATURE VEIN FUSION IN STEMS, TWO SEEMINGLY DISTINCT PROCESSES THAT BOTH SEVERELY DECREASE VEIN DENSITY. THIS INDICATES THAT THE NORMAL FUNCTIONS OF THESE TWO GENES ARE TO INITIATE INTERMEDIATE VEINS AS WELL AS PREVENT THEIR PREMATURE FUSION. PRELIMINARY ANALYSIS INDICATED THAT GENES RELATED TO THE PLANT HORMONE AUXIN ARE DIFFERENTIALLY EXPRESSED IN THE DOUBLE MUTANTS, LINKING THESE VASCULAR PHENOTYPES TO ALTERATIONS IN AUXIN METABOLISM OR SIGNALING. WE WILL INVESTIGATE HOW BLH12 AND BLH14 ACHIEVE THEIR DIFFERENT FUNCTIONS USING EXPRESSION PROFILING OF DIFFERENT TISSUES, PROTEOMICS TO IDENTIFY INTERACTING PARTNERS, IDENTIFYING DOWNSTREAM TARGET GENES, AND THROUGH CREATING A SERIES OF TRANSGENIC PLANTS TO ASSAY THE VASCULAR EFFECTS OF EXPRESSING BLH12/14 ALONE OR WITH THEIR PARTNERS.