Plants encounter diverse pathogens and have evolved a two-layered innate immune system to detect pathogen molecules and activate defense mechanisms that restrict infection. Most cloned plant Resistance (R) genes encode NLR immune receptors. NLR genes are often found in clusters of paralogs with sequence and copy number variation; whether these NLR clusters evolve in response to single or multiple pathogens has been unclear. We report here the isolation of a Phytophthora capsici resistance gene, Rpc2, along with a novel P. infestans resistance gene, Rpi-amr5, from two Solanum americanum accessions. These orthologous genes reside in the Rpi-amr1 cluster, which has previously been associated with resistance to P. infestans. By screening RXLR effector libraries of P. infestans and P. capsici, we identified multiple effectors recognized by both NLRs. Our findings highlight the complexity of NLR clusters and evolution driven by interactions with multiple pathogens. This work will underpin efforts to elevate resistance against Phytophthora pathogens and enhances our understanding of NLR evolution.

Precise ligand recognition by closely related leucine-rich repeat receptor kinases (LRR-RKs) is essential for plants to coordinate immunity, development, and environmental adaptation. Here, we show how HAESA-LIKE 3 (HSL3) specifically recognizes the folded, disulfide-stabilized CTNIP/SCREW phytocytokines in Arabidopsis. Quantitative binding assays define a minimal CTNIP4 region required for high-affinity HSL3 interaction and signaling activation. A 2.12 Å crystal structure of the HSL3-CTNIP4 complex reveals a unique C-terminal receptor pocket that accommodates the peptide’s cyclic architecture through a combination of hydrophobic and polar contacts, a feature absent in the closely related HAE/HSL LRR-RKs. The cyclic CTNIP4 fold further establishes a largely hydrophobic interface that bridges HSL3 to the SERK co-receptor, forming a distinct activation surface. Together, these structural, biochemical and physiological insights uncover a previously unrecognised mechanism of peptide perception and receptor activation, highlighting how subtle architectural variations enable precise ligand selectivity among highly conserved plant receptor kinases.

Pattern-triggered immunity (PTI) is initiated when plants detect pathogen-associated molecular patterns (PAMPs) through pattern-recognition receptors (PRRs). How moderate increases in temperature affect this plant immune signalling remains unclear. We explored this by using flg22 and the leucine-rich repeat receptor kinase (LRR-RK) FLS2 as a model receptor-ligand system and Ca2+ signaling as a representative PTI output. A pre-treatment at 28 °C significantly impaired the flg22-induced [Ca2+]cyt influx, leading to a reduced expression of calcium-dependent defence genes, ICS1 and EDS1. This effect correlated with a temperature-dependent reduction in FLS2 abundance. A qualitatively similar inhibition of these responses was observed when membrane fluidity was artificially increased using benzyl alcohol. This suggests that the effect of elevated temperature might act through changes in membrane properties. Artificially restoring FLS2 protein levels rescued flg22-dependent Ca2+ signalling and ICS1 and EDS1 expression in seedlings pre-treated at 28°C or with benzyl alcohol. Together, these findings indicate that increased membrane fluidity reduces FLS2 protein levels, thereby compromising Ca2+ signalling, and probably other, flg22-indcued responses. This highlights a potential mechanistic link between temperature perception, membrane fluidity, and FLS2-dependent calcium signalling, providing insight into how an increase in global temperatures may compromise plant immune responses in the future.

The morphology of starch granules is a major determinant of the functional and nutritional properties of starch and is highly variable among cereal species. Much of this morphological variation stems from differences in the spatial and temporal patterns of starch granule initiation in amyloplasts during grain development. Simple granules are thought to arise from a single initiation per amyloplast (e.g., in Brachypodium distachyon), whereas compound granules develop from multiple initiations per amyloplast (e.g., in rice). Using live-cell imaging in transgenic Brachypodium lines expressing a fluorescent amyloplast reporter construct, we discovered that simple-type starch granules in Brachypodium can arise from multiple initiations per amyloplast. The amyloplasts showed dynamic changes in their structure, the formation of stromules, and the movement of both the amyloplast within the cell and the starch granules within the amyloplasts. Our results suggest complex and pleiomorphic amyloplast organisation and mobility that can influence starch granule formation and morphology. This goes beyond the existing ‘one granule, one amyloplast’ model for simple-type granules, and advances our understanding of both amyloplast biogenesis and granule formation.

Plant cells survey and modulate their cell walls to control their shape and anisotropic growth. Signaling mediated by the plant steroid hormones brassinosteroids (BR) plays a central role in coordinating cell wall status and cell growth, and alterations in the cell wall-BR feedback loop leads to life-threatening defects in tissue and cellular integrity. How the status of the cell wall is relayed to BR signaling remains largely unclear. Increasing evidence shows that RAPID ALKALANIZATION FACTORs (RALFs), a class of secreted peptides, play structural and signaling roles at the cell surface. Here, we show that loss of RALF signaling mediated by the plasma membrane-localized RALF receptor complex FERONIA (FER)-LORELEI-LIKE GPI-anchor protein 1 (LLG1) leads to defects in cell morphology, organization, and composition of the cell wall-including pectin methylation status-and to an increase in BR signaling. We observed that increase in BR signaling mitigates the cellular defects associated with the loss of FER-mediated RALF signaling. We show that perception of RALF23 promotes the formation and signaling activity of the main BR receptor complex formed by BRASSINOSTEROID INSENSITIVE 1 (BRI1) and BRI1-ASSOCIATED KINASE 1 (BAK1) and that its bioactivity relies on pectin status. Our observations suggest a model in which RALF peptides operate at the nexus between cell wall status and BR signaling, capable of inducing changes in the cell wall as well as functioning as a cell-wall-informed signaling cues initiating a feedback loop that solicits BR signaling and coordinates cell morphogenesis.

Angiosperm seed formation requires the coordinated development of the products of double fertilization, the embryo and the endosperm. The endosperm mediates efficient nutrient transfer from surrounding maternal tissues to the developing embryo. This function requires a polarized tissue organization, which manifests as early polar gene expression and polar cellularization dynamics. We show that the receptor kinase HAIKU2 acts in coordination with the transcription factor WRKY10/MINISEED3 to ensure robust endosperm polarity establishment through the activity of the homeodomain transcription factors WUSCHEL-RELATED HOMEOBOX 8 and 9. This process depends on egg cell fertilization and is mediated through the peptide PATHOGEN-INDUCED PEPTIDE-LIKE 7, which acts as a HAIKU2 ligand. Our results reveal how a molecular paracrine dialogue between the embryo and endosperm ensures optimal seed developmental coordination.

Lichens are symbiotic associations between filamentous fungi and photosynthetic micro-organisms, such as algae or cyanobacteria, that result in a single anatomically-complex structure that can thrive in environments inhospitable to most organisms, including arctic tundra, high mountains, and deserts. Recent evidence suggests that lichens may be even more complex than previously appreciated, containing multiple microbial constituents that operate as mini-ecosystems, but how genomes of the principal fungal symbiont (which provides the majority of biomass in lichen tissue) have been shaped during evolution is largely unexplored. Recently, giant transposable elements called Starships have been found in many genomes of filamentous fungi, but to which extent they occur in lichen-forming fungi is not known. In this report, we describe a Starship-like element from the lichen fungus Xanthoria parietina. This element, named Tangerine, contains several genes that have signatures of horizontal gene transfer from non-lichen-forming fungi, most likely from black yeasts of the Chaetothyriales, that are often lichen-associated. Furthermore, the “captain” gene responsible for transposition of the Starship defines a small lichen-specific clade of tyrosine recombinases within clade 1 of the tyrosine recombinase typology, suggesting a longstanding association of these elements with lichen-forming fungi. Internal repeats within Tangerine, and other sites in Xanthoria genomes, are affected by repeat-induced point mutation (RIP), a mechanism of genome defense against transposable elements, consistent with fungal sexual reproduction which always precedes new lichen formation by Xanthoria. We conclude that Starships may have played a significant, yet hitherto unrecognized role, in lichen genome evolution.

Intracellular immune receptors protect plants from microbial invasion by detecting and responding to pathogen-derived effector molecules, often triggering cell death responses. However, pathogen effectors can evolve to avoid immune recognition, resulting in devastating diseases that threaten global agriculture. Here, we show that an integrated Exo70 domain from the barley NLR RGH2 can interact with both the rice blast pathogen effector AVR-Pii and a closely related wheat blast variant. We used structure-led engineering to develop RGH2+ that shows increased binding affinity towards AVR-Pii variants and increased cell death responses on heterologous expression in Nicotiana benthamiana. Infection assays in transgenic barley lines carrying RGH2+ with the paired NLR RGH3 indicate a reduced susceptibility to blast strains expressing AVR-Pii variants. These results demonstrate the potential of engineering NLR receptors as an effective strategy for improving resistance towards one of the most destructive diseases affecting cereal production.

Effector-triggered immunity (ETI) is a major defence strategy in plants and is frequently associated with the hypersensitive response (HR), a localized form of programmed cell death long assumed to be essential for pathogen resistance. However, the causal relationship between HR and effective immunity remains unresolved. We show that the Arabidopsis cbp60g sard1 double mutant exhibits exaggerated ETI-associated HR but only partial resistance to bacterial and oomycete pathogens, thereby genetically uncoupling cell death from disease resistance without pleiotropic defects. Genome-wide transcriptome profiling reveals that the absence of CBP60g and SARD1 disrupts the balance between immune activators and suppressors, including reduced induction of the Nudix hydrolase NUDT7. Overexpression of NUDT7 diminishes but does not abolish the heightened HR phenotype in cbp60g sard1 mutant, indicating that multiple negative regulators act redundantly to restrain immune-associated cell death. These findings demonstrate that HR is not an obligatory determinant of effective resistance and provide mechanistic insight into how plants coordinate transcriptional networks to balance pathogen defence with the containment of host cell death. By refining the relationship between HR and immunity, this work challenges a long-standing paradigm in plant biology and advances our understanding of immune regulation.