The plot of the first principal components of the genome-wide gene expression profile of five tissues in O. longistaminata revealed by the microarray expression analysis. PC1 is principal component 1, PC2 is principal component 2, and PC3 is principal component 3. Each type of tissue occupies a distinct location in the principal component space. PC1 separates leaves and shoot internodes from the other three organs. PC2 distinguishes among tips, internodes, and leaves. PC3 separates tips from internodes.