There are two major modes for plant recognition of biotrophic microbial pathogens. In one mode, plant pattern recognition receptors (PRRs) recognize microbe associated molecular patterns (MAMPs, also called PAMPs), which are molecules such as flg22, a fragment of bacterial flagellin. In the other mode, the products of plant resistance (R) genes recognize pathogen effectors or host proteins modified by effectors. Salicylic acid (SA) -mediated defense responses are an important part of R gene-mediated resistance. It was not clear how these two signaling mechanisms interact with each other. Recendy, we reported that treatment with flg22 triggered SA accumulation in Arabidopsis leaves. Disruptions of SA signaling components strongly affected MAMP-triggered gene expression responses. Flg22-triggered resistance to Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) was partly dependent on SA signaling. Our results demonstrated the importance of SA signaling in flg22-triggered resistance and, at the same time, the importance of some other signaling mechanism(s) in this resistance. Here we discuss potential signaling components of flg22-triggered SA accumulation and other signaling mechanisms potentially contributing to flg22-triggered resistance to Pst DC3000.
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Therefore, MAPK cascades could be upstream signaling components Our study revealed one type of interaction between MAMP-trig- for SA accumulation. MAPK3 and MAPK6 are activated by flg22, gered and SA-mediated signaling: MAMP perception triggers SA but it is not known whether they are involved in activating SA accu-accumulation. However, the interaction among signaling mecha- mulation. Supporting the idea that MAPK cascades are involved, nisms involved in the MAMP-triggered response is clearly complex, overexpression of AtMKK7, which encodes MAPKK7, leads to high and more research is needed to reveal all the relationships. levels of SA accumulation.22 Furthermore, ATMKK7 transcription is induced by flg22 treatment. However, we found that flg22-triggered Acknowledgements induction of PR-1, a good marker gene for SA accumulation,23 was Peethambaran for helpful comments. This work was supported by We thank Raka Mitra, Chris Botanga, Masanao Sato and Bela that MAPKK7 is not required for flg22-induced SA accumulation grant IOS-0419648 from the NSF Arabidopsis not compromised in atmkk7antisense transgenic plants, suggesting distribute.2010 program to
- Expression profiling
- Salicylic acid (SA)