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

Abstract

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.

TaADF7, an actin‐depolymerizing factor, contributes to wheat resistance against Puccinia striiformis f. sp. tritici

“…As an important resistance pathway against biotrophs, salicylic acid (SA), which is required for mounting the HR against an invading pathogen, induces the expression of PR genes and systemic acquired resistance (Hayat et al ., ; Takatsuji et al ., ). In TaADF7 knock‐down plants, the growth of Pst hypha increased and sporadic urediniospores occurred compared with that in control plants when inoculated with avirulent Pst .…”

Propesticides and their use as agrochemicals

“…Different studies have shown that acibenzolar‐ S ‐methyl may be considered as a functional analogue of salicylic acid in the pathway leading to SAR and might act at the same binding site. Finally, acibenzolar‐ S ‐methyl‐induced resistance in rice could depend on two complementary pathways – non‐expresser of pathogenesis‐related genes (NPR1) and the transcription factor Oryza sativa WRKY45 (OsWRKY45) – with the latter being crucial for blast resistance, induced not only by acibenzolar‐ S ‐methyl but also by other products …”

“…Finally, acibenzolar-S-methyl-induced resistance in rice could depend on two complementary pathways -non-expresser of pathogenesis-related genes (NPR1) and the transcription factor Oryza sativa WRKY45 (OsWRKY45) -with the latter being crucial for blast resistance, induced not only by acibenzolar-S-methyl but also by other products. 83…”

CC-NBS-LRR-Type R Proteins for Rice Blast Commonly Interact with Specific WRKY Transcription Factors

“…However, Pb1 encodes an R protein-like CC-NB-LRR protein with atypical NB domain . Our recent studies showed that Pb1 specifically interacts with rice WRKY45 (Shimono et al 2007(Shimono et al , 2012Takatsuji et al 2010;Nakayama et al 2013;Akagi et al 2014;Takatsuji 2014), a TF that plays a major role in the salicylic acid signaling pathway, and that the blast resistance due to Pb1 is dependent on WRKY45 . Rice WRKY45 is regulated by ubiquitin-proteasome degradation in the nuclei to suppress untimely defense activation in the absence of pathogen infection .…”