Novel stripe rust effector boosts the transcription of a host susceptibility factor through affecting histone modification to promote infection in wheat

A Conserved Endonuclease From Rust Fungi Suppresses Plant Extracellular DNA-Triggered Immunity

Nuclease 1 (NUC1) is a highly conserved nonspecific endonuclease present in vertebrates, fungi, and a few plant species. While the involvement of yeast NUC1p in apoptotic cell death independent of metacaspase or apoptosis-inducing factors is documented, its function in other fungi, particularly pathogenic ones, remains elusive. In this study, we identified and characterised the homologue of yeast NUC1p, termed PstNUC1, in Puccinia striiformis f. sp. tritici (Pst), the causal agent of wheat stripe rust. PstNUC1 was induced during infection and was secreted to the extracellular space of the host. Silencing of PstNUC1 significantly attenuated the virulence of Pst, suggesting its critical role in pathogenicity. Exogenous treatment of PstNUC1 diminished the extracellular DNA (exDNA)-triggered plant immune response, including cell death, oxygen peroxide production, and upregulation of Pathogenesis-related genes. Notably, overexpression of wild-type PstNUC1, but not a signal peptide-deficient mutant (PstNUC1ΔSP), in wheat compromised exDNA-triggered immunity, resulting in enhanced susceptibility to Pst infection. These finding collectively highlight the contribution of PstNUC1 to virulence through degradation of exDNA, thereby dampening the exDNA-induced plant immune response.

Epigenetic perspectives on wheat speciation, adaptation, and development

Bread wheat (Triticum aestivum) has undergone a complex evolutionary history shaped by polyploidization, domestication, and adaptation. Recent advances in multiomics approaches have shed light on the role of epigenetic mechanisms, including DNA methylation, histone modification, chromatin accessibility, and noncoding RNAs, in regulating gene expression throughout these processes. Epigenomic reprogramming contributes to genome stability and subgenome differentiation and modulates key agronomic traits by influencing flowering time, environmental responses, and developmental programs. This review synthesizes current insights into epigenetic regulation of wheat speciation, adaptation, and development, highlighting their potential applications in crop improvement. A deeper understanding of these mechanisms will facilitate targeted breeding strategies leveraging epigenetic variations to enhance wheat resilience and productivity in the face of changing environments.

Coordinated transcriptomic and metabolomic responses in rice reveal lignin-based physical barriers as key mechanisms of nonhost resistance to rust fungi

Nonhost resistance (NHR) serves as a fundamental defense response in plants against non-adapted pathogens, yet its underlying molecular mechanisms remain poorly understood. This study investigates the rice-Pst (Puccinia striiformis f. sp. tritici) interaction using integrated transcriptomic and metabolomic analyses to unravel the temporal dynamics of gene expression and metabolite changes associated with NHR. Our findings reveal a temporally coordinated activation of defense responses, with early induction of receptor-like kinases (RLKs) and hypersensitive response proteins, followed by later activation of jasmonic acid and systemic acquired resistance pathways, along with the accumulation of amino acids and other phenolic compounds. Notably, metabolic pathways related to cell wall reinforcement were significantly upregulated during Pst infection, highlighted by enhanced lignin biosynthesis (phenylpropanoid pathway), nucleotide sugar metabolism, and tryptophan pathways. Rice mutants deficient in genes involved in lignin biosynthesis (OsPAL3, Os4CL3, Os4CL5, and OsCCoAOMT) displayed reduced lignin deposition at infection sites and compromised resistance to Pst, underscoring a critical role of lignin-based physical barriers in NHR. This study provides novel insights into the molecular framework of rice NHR, emphasizing the pivotal role of structural defenses in plant immunity.

The Puccinia striiformis effector Pst11215 manipulates mitochondria to suppress host immunity by promoting TaVDIP1-mediated ubiquitination of TaVDAC1

Mitochondria-induced cell death is closely correlated with plant immune responses against pathogens. However, the molecular mechanisms by which pathogens manipulate mitochondria to suppress host resistance remain poorly understood. In this study, a haustorium-specific effector Pst11215 from the wheat stripe rust pathogen Puccinia striiformis f. sp. tritici (Pst) was characterized by host-induced gene silencing. The interaction partners regulated by Pst11215 were screened using the yeast two-hybrid system. In addition, Pst11215-mediated immune regulation modes were further determined. The results showed that Pst11215 was required for Pst virulence. Pst11215 interacted with the wheat voltage-dependent anion channel TaVDAC1, the negative regulator of wheat resistance to stripe rust, in mitochondria. Furthermore, the E3 ubiquitin ligase TaVDIP1 targeted and ubiquitinated TaVDAC1, which can be promoted by Pst11215. TaVDIP1 conferred enhanced wheat susceptibility to Pst by cooperating with TaVDAC1. Overexpression of TaVDIP1 reduced reactive oxygen species (ROS) accumulation and abnormal mitochondria. Our study revealed that Pst11215 functions as an important pathogenicity factor secreted to the host mitochondria to compromise wheat resistance to Pst possibly by facilitating TaVDIP1-mediated ubiquitination of TaVDAC1, thereby protecting mitochondria from ROS-induced impairment. This research unveils a novel regulation mode of effectors hijacking host mitochondria to contribute to pathogen infection.

Stripe Rust Effector Pst_9302 Inhibits Wheat Immunity to Promote Susceptibility

Puccinia striiformis f. sp. tritici is an obligate biotrophic fungus that causes destructive stripe rust disease in wheat. During infection, Pst secretes virulence effectors via a specific infection structure-the haustorium-inside host cells to disturb host immunity and promote fungal colonization and expansion. Hence, the identification and functional analyses of Pst effectors are of great significance in deciphering the Pst pathogenicity mechanism. Here, we identified one candidate Pst effector Pst_9302 that could suppress Bax-triggered cell death in Nicotiana benthamiana. qRT-PCR analyses showed that the transcript levels of Pst_9302 were highly increased during the early infection stages of Pst. The transient expression of Pst_9302 in wheat via the type-three secretion system (T3SS) significantly inhibited the callose deposition induced by Pseudomonas syringae EtHAn. During wheat-Pst interaction, Pst_9302 overexpression suppressed reactive oxygen species (ROS) accumulation and cell death caused by the avirulent Pst race CYR23. The host-induced gene silencing (HIGS) of Pst_9302 resulted in decreased Pst pathogenicity with reduced infection area. The results suggest that Pst_9302 plays a virulence role in suppressing plant immunity and promoting Pst pathogenicity. Moreover, wheat voltage-dependent anion channel 1 protein (TaVDAC1) was identified as candidate Pst_9302-interacting proteins by yeast two-hybrid (Y2H) screening. Pull-down assays using the His-Pst_9302 and GST-TaVDAC1 protein verified their interactions. These results suggest that Pst_9302 may modulate wheat TaVDAC1 to regulate plant immunity.