Salicylic Acid Signaling Pathway in Rice and the Potential Applications of Its Regulators

The salicylic acid (SA) signaling pathway plays a crucial role in systemic acquired resistance in dicots. Several chemical inducers, which are also called plant activators, such as benzothiadiazole (BTH), protect plants from diseases by acting on the SA signaling pathway. Several studies by us and other groups have revealed that rice also has the SA signaling pathway that shares signaling components with the SA signaling pathway in dicots. OsNPR1 is a rice counterpart of NPR1, a transcriptional coactivator that plays a central role in the SA pathway in Arabidopsis. OsWRKY45 is a BTH-inducible rice-specific transcription factor. Knockdown experiments have demonstrated that both these transcriptional regulators are essential for BTH-induced blast resistance in rice. Unlike the SA pathway in Arabidopsis, wherein most of the SA/BTH-regulated genes are controlled by NPR1, the pathway in rice branches into OsNPR1- and OsWRKY45-dependent pathways. OsWRKY45 overexpression confers very high resistance to blast and leaf blight diseases in rice, and it causes only minor growth retardation through the priming effect-an action mechanism characteristic of plant activators. OsWRKY45 is a potential target for genetic manipulation of rice in order to confer broad-spectrum disease resistance; however, it is necessary to improve the construct to drive OsWRKY45 expression in rice in order to optimize the growth and disease resistance of the plants. Here, we have reviewed recent advances in the studies on the SA pathway in rice, with particular focus on the potential practical applications of the signaling components.