Stripe rust effector Pst21674 compromises wheat resistance by targeting transcription factor TaASR3.

Pathogens compromise host defense responses by strategically secreting effector proteins. However, the molecular mechanisms by which effectors manipulate disease-resistance factors to evade host surveillance remain poorly understood. In this study, we characterized a Puccinia striiformis f. sp. tritici (Pst) effector Pst21674 with a signal peptide. Pst21674 was significantly upregulated during Pst infections in wheat (Triticum aestivum L.) and knocking down Pst21674 by host-induced gene silencing led to reduced Pst pathogenicity and restricted hyphal spread in wheat. Pst21674 interaction with the abscisic acid-, stress-, and ripening-induced protein TaASR3 was validated mainly in the nucleus. Size exclusion chromatography, bimolecular fluorescence complementation, and luciferase complementation imaging assays confirmed that TaASR3 could form a functional tetramer. Virus-induced gene silencing and overexpression demonstrated that TaASR3 contributes to wheat resistance to stripe rust by promoting accumulation of reactive oxygen species and cell death. Additionally, transcriptome analysis revealed that the expression of defense-related genes was regulated in transgenic wheat plants overexpressing TaASR3. Interaction between Pst21674 and TaASR3 interfered with the polymerization of TaASR3 and suppressed TaASR3-mediated transcriptional activation of defense-related genes. These results indicate that Pst21674 serves as an important virulence factor secreted into the host nucleus to impede wheat resistance to Pst, possibly by targeting and preventing polymerization of TaASR3.

A novel citrate synthase isoform contributes infection and stress resistance of the stripe rust fungus.

The early development of a rust fungus is dependent on the endogenous lipids stored in the urediniospores. After it establishes a parasitic relationship with the host, sugars absorbed from the host cells by haustoria become the primary nutrients. The tricarboxylic acid (TCA) cycle is essential to oxidize these nutrients. However, few studies have addressed the role of citrate synthase (CS), a rate-limiting enzyme of the TCA cycle, during the infection process of rust fungi. In this study, a CS gene from Puccinia striiformis f. sp. tritici (Pst), PsCS1, was cloned and characterized. Transcripts of PsCS1 and the enzyme activity of the CS were increased in the early Pst infection stage. Biochemical features and subcellular localization revealed that PsCS1 encoded a mitochondrial CS. Size exclusion chromatography, yeast two-hybrid and bimolecular fluorescence complementation experiments confirmed that PsCS1 could form a functional homo-octamer. The overexpression of PsCS1 enhanced the resistance of Escherichia coli to salt stress. The knockdown of PsCS1 using a host-induced gene silencing (HIGS) system blocked Pst growth in wheat. These results indicate that PsCS1 is required for nutrient metabolism in Pst and contributes to Pst infection by regulating ATP production and the supply of carbon sources.