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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. [ABSTRACT FROM AUTHOR]

Summary 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. [ABSTRACT FROM AUTHOR]

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 , SWR1c and H2A.Z have been shown to control 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 understood. In this study, we analyzed the roles of the SWR1c 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 SWR1c 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 SWR1c components and H2A.Z also resulted in compromised jasmonic acid/ethylene-mediated immunity. Genome-wide expression analyses similarly reveal distinct roles for H2A.Z and SWR1c components in gene regulation, and suggest 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 SWR1c components could have non-redundant functions in plant immunity and gene regulation. [ABSTRACT FROM AUTHOR]

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., (© The Author(s) 2016. Published by Oxford University Press on behalf of Nucleic Acids Research.)

MAPK (Mitogen-Activated Protein Kinases) mutants which are active independently of phosphorylation by upstream MAPK Kinases (MAPKKs) help to clarify signal transduction processes through MAPK modules and provide a useful tool to understand MAPK roles in the cell. The identification of such mutations is tricky. In this chapter, we provide a detailed protocol for their screening, taking advantage of a functional expression assay in yeast.

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.