Incorporation of the histone variant H2A.Z into nucleosomes by the SWR1 chromatin remodeling complex is a critical step in eukaryotic gene regulation. In Arabidopsis, SWRlc and H2A.Z have been shown ...to con- trol gene expression underlying development and environmental responses. Although they have been implicated in defense, the specific roles of the complex subunits and H2A.Z in immunity are not well under- stood. In this study, we analyzed the roles of the SWRlc subunits, PHOTOPERIOD-INDEPENDENT EARLY FLOWERING1 （PIE1）, ACTIN-RELATED PROTEIN6 （ARP6）, and SWR1 COMPLEX 6 （SWC6）, as well as H2A.Z, in defense and gene regulation. We found that SWRlc components play different roles in resistance to different pathogens. Loss of PIE1 and SWC6 function as well as depletion of H2A.Z led to reduced basal resistance, while loss of ARP6 fucntion resulted in enhanced resistance. We found that mutations in PIE1 and SWC6 resulted in impaired effector-triggered immunity. Mutation in SWRlc components and H2A.Z also resulted in compromised jasmonic acid/ethylene-mediated immunity. Genome-wide expres- sion analyses similarly reveal distinct roles for H2A.Z and SWRlc components in gene regulation, and sug- gest a potential role for PIE1 in the regulation of the cross talk between defense signaling pathways. Our data show that although they are part of the same complex, Arabidopsis SWRlc components could have non-redundant functions in plant immunity and gene regulation.
Plant mitogen-activated protein kinases (MAPKs) are involved in important processes, including stress signaling and development. In a functional yeast screen, we identified mutations that render ...Arabidopsis thaliana MAPKs constitutively active (CA). Importantly, CA-MAPKs maintain their specificity toward known activators and substrates. As a proof-of-concept, Arabidopsis MAPK4 (MPK4) function in plant immunity was investigated. In agreement with the phenotype of mpk4 mutants, CA-MPK4 plants were compromised in pathogen-induced salicylic acid accumulation and disease resistance. MPK4 activity was found to negatively regulate pathogen-associated molecular pattern-induced reactive oxygen species production but had no impact on callose deposition, indicating that CA-MPK4 allows discriminating between processes regulated by MPK4 activity from processes indirectly affected by mpk4 mutation. Finally, MPK4 activity was also found to compromise effector-triggered immunity conditioned by the Toll Interleukin-1 Receptor—nucleotide binding (NB)—Leu-rich repeat (LRR) receptors RPS4 and RPP4 but not by the coiled coil—NB-LRR receptors RPM1 and RPS2. Overall, these data reveal important insights on how MPK4 regulates plant defenses and establishes that CA-MAPKs offer a powerful tool to analyze the function of plant MAPK pathways.
Plants are a tremendous source of diverse chemicals, including many natural product-derived drugs. It has recently become apparent that the genes for the biosynthesis of numerous different types of ...plant natural products are organized as metabolic gene clusters, thereby unveiling a highly unusual form of plant genome architecture and offering novel avenues for discovery and exploitation of plant specialized metabolism. Here we show that these clustered pathways are characterized by distinct chromatin signatures of histone 3 lysine trimethylation (H3K27me3) and histone 2 variant H2A.Z, associated with cluster repression and activation, respectively, and represent discrete windows of co-regulation in the genome. We further demonstrate that knowledge of these chromatin signatures along with chromatin mutants can be used to mine genomes for cluster discovery. The roles of H3K27me3 and H2A.Z in repression and activation of single genes in plants are well known. However, our discovery of highly localized operon-like co-regulated regions of chromatin modification is unprecedented in plants. Our findings raise intriguing parallels with groups of physically linked multi-gene complexes in animals and with clustered pathways for specialized metabolism in filamentous fungi.
Besides the deposition of storage reserves, seed maturation is characterized by the acquisition of functional traits including germination, desiccation tolerance, dormancy, and longevity. After seed ...filling, seed longevity increases up to 30-fold, concomitant with desiccation that brings the embryo to a quiescent state. The period that we define as late maturation phase can represent 10–78% of total seed development time, yet it remains overlooked. Its importance is underscored by the fact that in the seed production chain, the stage of maturity at harvest is the primary factor that influences seed longevity and seedling establishment. This review describes the major events and regulatory pathways underlying the acquisition of seed longevity, focusing on key indicators of maturity such as chlorophyll degradation, accumulation of raffinose family oligosaccharides, late embryogenesis abundant proteins, and heat shock proteins. We discuss how these markers are correlated with or contribute to seed longevity, and highlight questions that merit further attention. We present evidence suggesting that molecular players involved in biotic defence also have a regulatory role in seed longevity. We also explore how the concept of plasticity can help understand the acquisition of longevity.
Temperature is a key seasonal signal that shapes plant growth. Elevated ambient temperature accelerates growth and developmental transitions 1 while compromising plant defenses, leading to increased ...susceptibility 2, 3. Suppression of immunity at elevated temperature is at the interface of trade-off between growth and defense 2, 4. Climate change and the increase in average growth-season temperatures threaten biodiversity and food security 5, 6. Despite its significance, the molecular mechanisms that link thermosensory growth and defense responses are not known. Here we show that PHYTOCHROME INTERACTING FACTOR 4 (PIF4)-mediated thermosensory growth and architecture adaptations are directly linked to suppression of immunity at elevated temperature. PIF4 positively regulates growth and development and negatively regulates immunity. We also show that natural variation of PIF4-mediated temperature response underlies variation in the balance between growth and defense among Arabidopsis natural strains. Importantly, we find that modulation of PIF4 function alters temperature sensitivity of defense. Perturbation of PIF4-mediated growth has resulted in temperature-resilient disease resistance. This study reveals a molecular link between thermosensory growth and immunity in plants. Elucidation of the molecular mechanisms that define environmental signal integration is key to the development of novel strategies for breeding temperature-resilient disease resistance in crops.
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•Transcription factor PIF4 coordinates thermosensory growth and immunity•PIF4 negatively regulates immunity, while promoting growth•Natural variation of PIF4 signaling underlies growth-defense balance in the wild•Modulation of PIF4 signaling alters temperature sensitivity of disease resistance
Gangappa et al. show that the transcription factor PIF4 coordinates thermosensory growth and immunity. PIF4 acts as a negative regulator of plant immunity, and modulation of its function alters the balance between growth and defense. Importantly, natural variation of PIF4 signaling underlies growth-defense balance in Arabidopsis natural strains.
Mitogen-activated protein kinases (MAPKs) are important regulators of plant immunity. Most of the knowledge about the function of these pathways is derived from loss-of-function approaches. Using a ...gain-of-function approach, we investigated the responses controlled by a constitutively active (CA) MPK3 in Arabidopsis thaliana. CA-MPK3 plants are dwarfed and display a massive derepression of defense genes associated with spontaneous cell death as well as the accumulation of reactive oxygen species, phytoalexins, and the stress-related hormones ethylene and salicylic acid (SA). Remarkably CA-MPK3/sid2 and CA-MPK3/ein2-50 lines, which are impaired in SA synthesis and ethylene signaling, respectively, retain most of the CA-MPK3-associated phenotypes, indicating that the constitutive activity of MPK3 can bypass SA and ethylene signaling to activate defense responses. A comparative analysis of the molecular phenotypes of CA-MPK3 and mpk4 autoimmunity suggested convergence between the MPK3- and MPK4-guarding modules. In support of this model, CA-MPK3 crosses with summ1 and summ2, two known suppressors of mpk4, resulted in a partial reversion of the CA-MPK3 phenotypes. Overall, our data unravel a novel mechanism by which the MAPK signaling network contributes to a robust defense-response system.
During the later stages of seed maturation, two key adaptive traits are acquired that contribute to seed lifespan and dispersal, longevity and dormancy. The seed‐specific heat shock transcription ...factor A9 is an important hub gene in the transcriptional network of late seed maturation. Here, we demonstrate that HSFA9 plays a role in thermotolerance rather than in ex situ seed conservation. Storage of hsfa9 seeds of Medicago truncatula and Arabidopsis had comparable lifespan at moderate storage relative humidity (RH), whereas at high RH, hsfa9 seeds lost their viability much faster than wild type seeds. Furthermore, we show that in M. truncatula, Mthsfa9 seeds acquired more dormancy during late maturation than wild type. Transient expression of MtHSFA9 in hairy roots and transcriptome analysis of Mthsfa9 Tnt1 insertion mutants identified a deregulation of genes involved in ABA biosynthesis, catabolism and signalling. Consistent with these results, Mthsfa9 seeds exhibited increased ABA levels and higher sensitivity to ABA. These data suggest that in legumes, HSFA9 acts as a negative regulator of the depth of seed dormancy during seed development via the modulation of hormonal balance.
The seed specific HSFA9 regulates the depth of dormancy during maturation in Medicago truncatula seeds via ABA signaling. Its presumed role in seed longevity is limited to wet and hot storage conditions, indicating a role in thermotolerance rather than ex situ seed conservation.
Mitogen-Activated Protein Kinase (MAPK) modules are often involved in stress responses and plant developmental processes. Among these MAPKs, MPK4 has a complex role in biotic stress signaling, cell ...division control and cytoskeletal organization. mpk4 knockout (KO) plants are dwarfed and very sick, making it difficult to distinguish between cause and effect of its phenotype. To overcome this difficulty, we developed mutations triggering constitutive MPK4 activity and created transgenic lines allowing phenotypic studies on a WT-like plant. By this approach, we confirmed that MPK4 functions as a negative regulator of pathogen defense, but our work also suggests that MPK4 interferes with stress signaling pathways at several distinct steps in pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) as well as in effector-triggered immunity (ETI). This study shows that CA mutations are valuable complementary tools to study MAPK signaling pathways in planta.
The stress-activated MPK3 and the SUPPRESSOR OF MKK1 MKK2 1/2 module control a similar set of responses, which include accumulation of salicylic acid, reactive oxygen species, and phytoalexins and ...modulation of defense genes.
Mitogen-activated protein kinases (MAPKs) are important regulators of plant immunity. Most of the knowledge about the function of these pathways is derived from loss-of-function approaches. Using a gain-of-function approach, we investigated the responses controlled by a constitutively active (CA) MPK3 in
Arabidopsis thaliana
.
CA-MPK3
plants are dwarfed and display a massive derepression of defense genes associated with spontaneous cell death as well as the accumulation of reactive oxygen species, phytoalexins, and the stress-related hormones ethylene and salicylic acid (
SA
). Remarkably
CA-MPK3
/
sid2
and
CA-MPK3
/
ein2-50
lines, which are impaired in
SA
synthesis and ethylene signaling, respectively, retain most of the
CA-MPK3
-associated phenotypes, indicating that the constitutive activity of MPK3 can bypass
SA
and ethylene signaling to activate defense responses. A comparative analysis of the molecular phenotypes of
CA-MPK3
and
mpk4
autoimmunity suggested convergence between the MPK3- and MPK4-guarding modules. In support of this model,
CA-MPK3
crosses with
summ1
and
summ2
, two known suppressors of
mpk4
, resulted in a partial reversion of the
CA-MPK3
phenotypes. Overall, our data unravel a novel mechanism by which the MAPK signaling network contributes to a robust defense-response system.
Mitogen-Activated Protein Kinase (MAPK) modules are often involved in stress responses and plant developmental processes. Among these MAPKs, MPK4 has a complex role in biotic stress signaling, cell ...division control and cytoskeletal organization. mpk4 knockout (KO) plants are dwarfed and very sick, making it difficult to distinguish between cause and effect of its phenotype. To overcome this difficulty, we developed mutations triggering constitutive MPK4 activity and created transgenic lines allowing phenotypic studies on a WT-like plant. By this approach, we confirmed that MPK4 functions as a negative regulator of pathogen defense, but our work also suggests that MPK4 interferes with stress signaling pathways at several distinct steps in pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) as well as in effector-triggered immunity (ETI). This study shows that CA mutations are valuable complementary tools to study MAPK signaling pathways in planta.
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