[show abstract][hide abstract] ABSTRACT: The molecular mechanisms underlying the trade-off between plant innate immunity and steroid-mediated growth are controversial. Here, we report that activation of the transcription factor BZR1 is required and sufficient for suppression of immune signaling by brassinosteroids (BR). BZR1 induces the expression of several WRKY transcription factors that negatively control early immune responses. In addition, BZR1 associates with WRKY40 to mediate the antagonism between BR and immune signaling. We reveal that BZR1-mediated inhibition of immunity is particularly relevant when plant fast growth is required, such as during etiolation. Thus, BZR1 acts as an important regulator mediating the trade-off between growth and immunity upon integration of environmental cues. DOI: http://dx.doi.org/10.7554/eLife.00983.001.
[show abstract][hide abstract] ABSTRACT: The Arabidopsis thaliana leucine-rich repeat receptor kinase FLAGELLIN SENSING2 (FLS2) is required for the recognition of bacterial flagellin in innate immunity. Recently, FLS2 was proposed to act as a multispecific receptor recognizing unrelated exogenous and endogenous peptide ligands, including CLAVATA3 (CLV3), a key regulator of shoot meristem stem cell production. Here, we report experimental evidence demonstrating that FLS2 does not recognize CLV3 and that the shoot apical meristem is immune to bacteria independently of CLV3 perception.
The Plant Cell 08/2012; 24(8):3186-92. · 9.25 Impact Factor
[show abstract][hide abstract] ABSTRACT: Detailed phenotypic characterization reveals that several BAK1 fusion proteins with C-terminal tags strongly impair complementation of bak1 null mutants with respect to responsiveness to the bacterial pathogen-associated molecular patterns flagellin and EF-Tu. This raises concerns about the widespread use of such protein variants of this important regulatory Leu-rich repeat receptor-like kinase (RLK) for functional analyses of RLK-based signaling.
The Plant Cell 11/2011; 23(11):3871-8. · 9.25 Impact Factor
[show abstract][hide abstract] ABSTRACT: Plants and animals use innate immunity as a first defense against pathogens, a costly yet necessary tradeoff between growth and immunity. In Arabidopsis, the regulatory leucine-rich repeat receptor-like kinase (LRR-RLK) BAK1 combines with the LRR-RLKs FLS2 and EFR in pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) and the LRR-RLK BRI1 in brassinosteroid (BR)-mediated growth. Therefore, a potential tradeoff between these pathways mediated by BAK1 is often postulated. Here, we show a unidirectional inhibition of FLS2-mediated immune signaling by BR perception. Unexpectedly, this effect occurred downstream or independently of complex formation with BAK1 and associated downstream phosphorylation. Thus, BAK1 is not rate-limiting in these pathways. BRs also inhibited signaling triggered by the BAK1-independent recognition of the fungal PAMP chitin. Our results suggest a general mechanism operative in plants in which BR-mediated growth directly antagonizes innate immune signaling.
Proceedings of the National Academy of Sciences 11/2011; 109(1):303-8. · 9.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: Our current understanding of pathogen-associated molecular pattern (PAMP)-triggered immunity signaling pathways in plants is limited due to the redundancy of several components or the lethality of mutants in Arabidopsis (Arabidopsis thaliana). To overcome this, we used a virus-induced gene silencing-based approach in combination with pharmacological studies to decipher links between early PAMP-triggered immunity events and their roles in immunity following PAMP perception in Nicotiana benthamiana. Two different calcium influx inhibitors suppressed the reactive oxygen species (ROS) burst: activation of the mitogen-activated protein kinases (MAPKs) and PAMP-induced gene expression. The calcium burst was unaffected in plants specifically silenced for components involved in ROS generation or for MAPKs activated by PAMP treatment. Importantly, the ROS burst still occurred in plants silenced for the two major defense-associated MAPK genes NbSIPK (for salicylic acid-induced protein kinase) and NbWIPK (for wound-induced protein kinase) or for both genes simultaneously, demonstrating that these MAPKs are dispensable for ROS production. We further show that NbSIPK silencing is sufficient to prevent PAMP-induced gene expression but that both MAPKs are required for bacterial immunity against two virulent strains of Pseudomonas syringae and their respective nonpathogenic mutants. These results suggest that the PAMP-triggered calcium burst is upstream of separate signaling branches, one leading to MAPK activation and then gene expression and the other to ROS production. In addition, this study highlights the essential roles of NbSIPK and NbWIPK in antibacterial immunity. Unexpectedly, negative regulatory mechanisms controlling the intensity of the PAMP-triggered calcium and ROS bursts were also revealed by this work.
[show abstract][hide abstract] ABSTRACT: The plant cell wall is a dynamic and complex structure whose functional integrity is constantly being monitored and maintained during development and interactions with the environment. In response to cell wall damage (CWD), putatively compensatory responses, such as lignin production, are initiated. In this context, lignin deposition could reinforce the cell wall to maintain functional integrity. Lignin is important for the plant's response to environmental stress, for reinforcement during secondary cell wall formation, and for long-distance water transport. Here, we identify two stages and several components of a genetic network that regulate CWD-induced lignin production in Arabidopsis (Arabidopsis thaliana). During the early stage, calcium and diphenyleneiodonium-sensitive reactive oxygen species (ROS) production are required to induce a secondary ROS burst and jasmonic acid (JA) accumulation. During the second stage, ROS derived from the NADPH oxidase RESPIRATORY BURST OXIDASE HOMOLOG D and JA-isoleucine generated by JASMONIC ACID RESISTANT1, form a negative feedback loop that can repress each other's production. This feedback loop in turn seems to influence lignin accumulation. Our results characterize a genetic network enabling plants to regulate lignin biosynthesis in response to CWD through dynamic interactions between JA and ROS.
[show abstract][hide abstract] ABSTRACT: The first active layer of plant innate immunity relies on the recognition by surface receptors of molecules indicative of non-self or modified-self. The activation of pattern-recognition receptors (PRRs) by pathogen-associated molecular patterns (PAMPs) is in essence sufficient to stop pathogen invasion through transcriptional reprogramming and production of anti-microbials. The few PRR/PAMP pairs that are characterised provide useful models to study the specificity of ligand-binding and likely activation mechanisms. Both classical and new approaches are still required to identify new bacterial PAMPs. Current genetic screens, functional genomics and biochemical analyses have identified the regulation mechanisms of PRR transcription and biogenesis, provided insights into the composition of PRR complexes at the plasma membrane and highlighted the roles of long-known signalling components in PAMP-triggered immunity (PTI).
Current opinion in microbiology 02/2011; 14(1):54-61. · 7.87 Impact Factor
[show abstract][hide abstract] ABSTRACT: In plant innate immunity, the leucine-rich repeat receptor kinase FLS2 recognizes the bacterial pathogen-associated molecular pattern (PAMP) flagellin. The molecular mechanisms underlying PAMP perception are not fully understood. Here, we reveal that the gaseous phytohormone ethylene is an integral part of PAMP-triggered immunity. Plants mutated in the key ethylene-signaling protein EIN2 are impaired in all FLS2-mediated responses, correlating with reduced FLS2 transcription and protein accumulation. The EIN3 and EIN3-like transcription factors, which depend on EIN2 activity for their accumulation, directly control FLS2 expression. Our results reveal a direct role for ethylene in regulation of an innate immune receptor.
Proceedings of the National Academy of Sciences 08/2010; 107(32):14502-7. · 9.74 Impact Factor