The rice pattern recognition receptor, XA21, confers robust resistance to the bacterial pathogen Xanthomonas oryzae pv. oryzae (Xoo). We have generated transgenic plants that express Xa21 only in the presence of the glucocorticoid hormone, dexamethasone (DEX). DEX-mediated transcriptional induction of Xa21 is accompanied by upregulation of pathogenesis-related 1 gene expression and restriction of Xoo multiplication. The DEX-inducible system can be used to synchronize the XA21-mediated response to infection throughout the entire leaf, facilitating the study of innate immunity.