Figure 11.

A model summarizing the defense responses of B73 and Mo17 against the aphid R. padi. Maize plants respond to R. padi feeding mainly by perceiving certain aphid-derived elicitors through unknown receptors, thereby transcriptionally up- or down-regulating TFs (transcription factors). In B73, more TFs are regulated than in Mo17 and most TFs are down-regulated, while in Mo17 most TFs are up-regulated. TFs and other pathways, including alternative splicing (AS), continuously shape the transcriptomes of B73 and Mo17, resulting in changes in defenses. Importantly, certain TFs, that are not regulated by R. padi herbivory, target the promoters of BX1 and BX13 and have higher activity in Mo17 than in B73, resulting in much higher expression levels of BX1 and BX13 and thus high contents of benzoxazinoids (Bxs) in Mo17. The promoters of BX1 and BX13 in Mo17 may also possess more cis-elements that allow more efficient transcription. I-3-GP: indole-3-glycerol phosphate; Red and blue arrows and circles represent B73 and Mo17, respectively. Up and down arrows in the circles indicate up-regulation or down-regulation, and the thickness of these arrows represent the numbers of genes. The sizes of the circles indicate the number of regulated TF genes and the size of letters represent activity, expression, or concentrations. Vertical lines connected with the boxes of BX1 and BX13 represent their promoters, and the horizontal bars symbolize cis-elements. Bxs are a group of metabolites produced by BX1 to BX14.