Abstract
We examined ways in which the Brown planthopper induced008a (Bphi008a; AY256682) gene of rice (Oryza sativa) enhances the plant's resistance to a specialist herbivore, the brown planthopper (BPH; Nilaparvata lugens). Measurement of the expression levels of ethylene synthases and of ethylene emissions showed that BPH feeding rapidly initiated the ethylene signaling pathway and up-regulated Bphi008a transcript levels after 6 to 96 h of feeding. In contrast, blocking ethylene transduction (using 1-methylcyclopropene) reduced Bphi008a transcript levels in wild-type plants fed upon by BPH. In vitro kinase assays showed that Bphi008a can be phosphorylated by rice Mitogen-activated Protein Kinase5 (OsMPK5), and yeast two-hybrid assays demonstrated that the carboxyl-terminal proline-rich region of Bphi008a interacts directly with this kinase. Furthermore, bimolecular fluorescence complementation assays showed that this interaction occurs in the nucleus. Subsequently, we found that Bphi008a up-regulation and down-regulation were accompanied by different changes in transcription levels of OsMPK5, OsMPK12, OsMPK13, and OsMPK17 in transgenic plants. Immunoblot analysis also showed that the OsMPK5 protein level increased in overexpressing plants and decreased in RNA interference plants after BPH feeding. In transgenic lines, changes in the expression levels of several enzymes that are important components of the defenses against the BPH were also observed. Finally, yeast two-hybrid screening results showed that Bphi008a is able to interact with a b-ZIP transcription factor (OsbZIP60) and a RNA polymerase polypeptide (SDRP).
Highlights
We examined ways in which the Brown planthopper induced008a (Bphi008a; AY256682) gene of rice (Oryza sativa) enhances the plant’s resistance to a specialist herbivore, the brown planthopper (BPH; Nilaparvata lugens)
Since the endogenous expression level of Bphi008a in wild-type plants was relatively low under normal growth conditions, the effectiveness of RNA interference (RNAi) in six T0 transgenic lines was examined in plants that had been infested with the BPH for 48 h
What signaling pathway(s) activated by extracellular stress are essential for plants to turn on the appropriate defense pathways in their innate immune systems? Our results indicate that when the BPH feeds on rice, upstream genes involved in Et production are rapidly up-regulated, within 6 h, and Et emission is continuously enhanced thereafter until 72 h (Fig. 3, A–C)
Summary
We examined ways in which the Brown planthopper induced008a (Bphi008a; AY256682) gene of rice (Oryza sativa) enhances the plant’s resistance to a specialist herbivore, the brown planthopper (BPH; Nilaparvata lugens). MAPK cascades constitute a group of evolutionarily conserved Ser/Thr-specific protein kinases in eukaryotic organisms These protein kinases can transduce extracellular stimuli into intracellular responses by either phosphorylating a target protein in the cytoplasm or directly translocating into the nucleus and regulating gene expression through the phosphorylation of specific transcription factors. These kinase cascade-mediated defense mechanisms are important signaling modules that are involved in the regulation of numerous abiotic and biotic stress responses (Jonak et al, 2002; Hamel et al, 2006; Howe and Jander, 2008). The cited studies indicate that the signaling events initiated by a diverse range of stresses have converged into a conserved MAPK cascade
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