Reprogramming of epigenetic states in gametes and embryos is essential for correct development in plants and mammals1. In plants, the germ line arises from somatic tissues of the flower necessitating erasure of chromatin modifications accumulated at specific loci during development or in response to external stimuli. If this occurs inefficiently it can lead to epigenetic states being inherited from one generation to the next2-4. However, in most cases accumulated epigenetic modifications are efficiently erased before the next generation. An important example of epigenetic reprogramming in plants is the resetting of expression of the Arabidopsis thaliana floral repressor FLC locus. FLC is epigenetically silenced by prolonged cold in a process called vernalization. However, the locus is reactivated prior to completion of seed development to ensure a vernalization requirement every generation. In contrast to our detailed understanding of the Polycomb-mediated epigenetic silencing induced by vernalization, little is known about the mechanism involved in the re-activation of FLC. Here we show that a hypomorphic mutation in the jumonji domain protein ELF6 impaired the reactivation of FLC in reproductive tissues, leading to inheritance of a partially vernalized state. ELF6 has H3K27me3 demethylase activity and the mutation reduced this enzymatic activity in planta. Consistent with this, H3K27me3 levels at the FLC locus stayed higher and FLC expression remained lower, than in the wild type in the following generation. Our data reveal an ancient role for H3K27 demethylation in the reprogramming of epigenetic states in plant and mammalian embryos5-7.

To establish infection, pathogens deploy effectors to modify or remove host proteins. Plant immune receptors with nucleotide-binding, leucine-rich repeat domains (NLRs) detect these modifications and trigger immunity. Plant NLRs thus guard host "guardees." A corollary is that autoimmunity may result from inappropriate NLR activation because mutations in plant guardees could trigger corresponding NLR guards. To explore these hypotheses, we expressed 108 dominant-negative (DN) Arabidopsis NLRs in various lesion mimic mutants, including camta3, which exhibits autoimmunity. CAMTA3 was previously described as a negative regulator of immunity, and we find that autoimmunity in camta3 is fully suppressed by expressing DNs of two NLRs, DSC1 and DSC2. Additionally, expression of either NLR triggers cell death that can be suppressed by CAMTA3 expression. These findings support a model in which DSC1 and DSC2 guard CAMTA3, and they suggest that other negative regulators of immunity may similarly represent guardees.

Receptor-like kinases (RLKs) are surface localized, transmembrane receptors comprising a large family of well-studied kinases. RLKs signal through their transmembrane and juxtamembrane domains with the aid of various interacting partners and downstream components. The N-terminal extracellular domain defines ligand specificity, and RLK families are sub-classed according to this domain. The most studied of these subfamilies include those with (1) leucine-rich repeat (LRR) domains, (2) LysM domains (LYM), and (3) the Catharanthus roseus RLK1-like (CrRLK1L) domain. These proteins recognize distinct ligands of microbial origin or ligands derived from intracellular protein/carbohydrate signals. For example, the pattern-recognition receptor (PRR) AtFLS2 recognizes flg22 from flagellin, and the PRR AtEFR recognizes elf18 from elongation factor (EF-Tu). Upon binding of their cognate ligands, the aforementioned RLKs activate generic immune responses termed pattern-triggered immunity (PTI). RLKs can form complexes with other family members and engage a variety of intracellular signaling components and regulatory pathways upon stimulation. This review focuses on interesting new data about how these receptors form protein complexes to exert their function.

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