A, Yeast two-hybrid (Y2H) assay of interactions between the Gal4 DNA binding domain BD-NF-YB2/3, BD-NF-YC3/4/9 and Gal4 activation domain AD-TOC1/5X fusions. Yeast growth shown on leucine-, tryptophan-deficient plate indicates successful plasmid transformation, and yeast growth shown on leucine-, tryptophan-, histidine-deficient and 3-AT plate indicates positive protein interactions. 