Determining the genes of unknown function that respond to drought or ABA treatment across species. Decision tree used to determine which genes and their orthologs were regulated by drought/ABA across different species (A). For each sorghum gene, the tree was traversed 3 times; once for each non-sorghum species: rice, maize, Arabidopsis. Venn diagram displaying the overlap of drought-responsive sorghum genes of unknown function that had drought-responsive orthologs of unknown function in other species (B). Each gene is found in 2 or more species.