The OsMPK15 Negatively Regulates Magnaporthe oryza and Xoo Disease Resistance via SA and JA Signaling Pathway in Rice

Abstract

Mitogen-activated protein kinase (MAPK) cascades play central roles in response to biotic and abiotic stresses. However, the mechanisms by which various MAPK members regulate the plant immune response in rice remain elusive. In this article, to characterize the mechanisms, the knock-out and overexpression mutants of OsMPK15 were constructed and the disease resistance was investigated under the various fungal and bacterial inoculations. The knock-out mutant of OsMPK15 resulted in the constitutive expression of pathogenesis-related ( PR ) genes, increased accumulation of reactive oxygen species (ROS) triggered by the pathogen-associated molecular pattern (PAMP) elicitor chitin, and significantly enhanced the disease resistance to different races of Magnaporthe oryzae and Xanthomonas oryzae pv. oryzae ( Xoo ), which cause the rice blast and bacterial blight diseases, respectively. On contrary, the expression of PR genes and ROS were down-regulated in the OsMPK15 -overexpressing (OsMPK15-OE) lines. Meanwhile, phytohormones such as salicylic acid (SA) and jasmonic acid (JA) were accumulated in the mpk15 mutant lines but decreased in the OsMPK15-OE lines. The expression of SA- and JA-pathway associated genes were significantly upregulated in the mpk15 mutant, whereas it was down regulated in the OsMPK15-OE lines. We conclude that OsMPK15 may negatively regulate the disease resistance through modulating SA- and JA-mediated signaling pathway.

Update on the Roles of Rice MAPK Cascades

“…OsMAPKKK1 acts as a positive regulator in ABA and ET signaling pathways, while as a negative regulator in JA and SA signaling pathways [12][13][14][15], implying that Os-MAPKKK1 probably interacts with different proteins or phosphorylates different downstream OsMAPKKs to play roles in diverse phytohormone signaling pathways. Similarly, OsMAPK4 positively regulates the accumulation of JA and SA, and OsMAPK17-1 positively regulates the accumulation of SA, while OsMAPK16 negatively regulates the accumulation of JA and SA, and OsMAPK20-5 negatively affects the synthesis of ET [40,43,48,49]. These data demonstrate that rice MAPK cascades regulate or involve in complex phytohormone accumulation, signaling pathways or response (Figure 4).…”

“…However, there is no direct evidence to confirm these two genes enhancing rice resistance to M. oryzae [20]. Of the four OsMAPKs to be involved in resistance to fungal pathogen, OsMAPK3 and OsMAPK16 negatively regulate resistance to M. oryzae [36,37,48], while OsMAPK20-5 positively confers resistance to M. oryzae [53]. OsMAPK6 is transcriptionally induced by sphingolipid elicitor and chitin, implying that OsMAPK6 possibly plays role in rice-M. oryzae interactions [33,34].…”

“…OsMAPKK3 also functions as a positive regulator but in response to Xoo by activating downstream OsMAPK7, with the signal transduction that the activated OsMAPK7 phosphorylates and activates the transcription factor OsWRKY30 to enhance rice resistance to Xoo [30]. Of the six OsMAPKs conferring resistance to bacterial pathogen, OsMAPK3 and OsMAPK16 play negative roles in response to Xoo [37,48], while OsMAPK7 and OsMAPK17-1 play positive roles in resistance to Xoo [30,49]. Interestingly, OsMAPK4 positively confers resistance to Xoo by promoting the accumulation of JA and SA, while it negatively influences resistance to Xoo by negatively regulating systemic acquired resistance, because both OsMAPK4 overexpressing plants and osmapk4 mutant exhibit enhanced resistance to Xoo [40,41].…”

“…The series of results suggest that different phytohormone signaling pathways can modulate OsMAPK6 function in diverse physiological processes, and OsMAPK6 could also phosphorylate different downstream substrates to regulate phytohormone homeostasis, fine-tuning rice growth and developmental responses as well as biotic and abiotic stress responses. [12][13][14][15]27,28,40,43,48,49]. The established OsMAPKKK62-Os-MAPKK3-OsMAPK7/14 cascades are regulated by ABA, while the OsMAPKKK10-OsMAPKK4-Os-MAPK6 cascade can regulate BR and CK signal transduction [17][18][19]24].…”

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“…oryzae) 40 . Similarly, the relative transcriptional level of PR genes was upregulated in OsMAPK15 (a negative regulatory gene for disease resistance in rice) knockout mutants, while chitin promoted an increase in the accumulation of ROS and significantly enhanced the resistance of rice to the two abovementioned diseases, and the opposite results were obtained in these gene overexpression lines 41 . In our study, we used DAB staining to visualize the accumulation of H 2 O 2 inside the leaf tissues (Fig.…”