The expression of both ZmPR-1 (Fig. 2AeB) and ZmNPR1 (Fig. 2CeD) was suppressed by inoculation and wounding at earlier time points in comparison to the levels observed during normal development in B73. In TZAR101, the expression of ZmPR-1 did not significantly vary over the time course. The expression of ZmNPR1, however, did not show suppression as observed in B73. This is interesting considering that the expression of AtPR-1 through AtNPR1 is essential to the induction of systemic required resistance (SAR) and SA-based biotrophic pathogen defense in A. thaliana [13]. Previous studies in the model species A. thaliana have demonstrated that AtNPR1 is mainly regulated at the protein level, particularly the post translational modification through salicylic acidemediated redox changes in the cells to regulate the depolymerization of the AtNPR1 oligomer and formation of functional monomers to induce appropriate defense responses in the presence of pathogen and its rapid turnover in proteasome in the absence of pathogen [61]. However, it has also beenproposed in the
literature that the NPR1 protein in maize and other monocot species may function in a different manner than that described for NPR1 in dicot species [62]. Further study will be required to fully characterize the function of NPR1 in maize and its interaction with ZmPR-1 in particular.