Search

Effectors are considered to be virulence factors secreted by pathogens, which play an important role during host-pathogen interactions. In this study, the candidate effector Pt9226 was cloned from genomic DNA of Puccinia triticina (Pt) pathotype THTT, and there were six exons and five introns in the 877 bp sequence, with the corresponding open reading frame of 447 bp in length, encoding a protein of 148 amino acids. There was only one polymorphic locus of I142V among the six Pt pathotypes analyzed. Bioinformatics analysis showed that Pt9226 had 96.46% homology with the hypothetical putative protein PTTG_26361 (OAV96349.1) in the Pt pathotype BBBD. RT-qPCR analyses showed that the expression of Pt9226 was induced after Pt inoculation, with a peak at 36 hpi, which was 20 times higher than the initial expression at 0 hpi, and another high expression was observed at 96 hpi. No secretory function was detected for the Pt9226-predicted signal peptide. The subcellular localization of Pt9226Δsp-GFP was found to be multiple, localized in the tobacco leaves. Pt9226 could inhibit programmed cell death (PCD) induced by BAX/INF1 in tobacco as well as DC3000-induced PCD in wheat. The transient expression of Pt9226 in 26 wheat near-isogenic lines (NILs) by a bacterial type III secretion system of Pseudomonas fluorescens EtHAn suppressed callose accumulation triggered by Ethan in wheat near-isogenic lines TcLr15, TcLr25, and TcLr30, and it also suppressed the ROS accumulation in TcLr15. RT-qPCR analysis showed that the expression of genes coded for pathogenesis-related protein TaPR1, TaPR2, and thaumatin-like protein TaTLP1, were suppressed, while the expression of PtEF-1α was induced, with 1.6 times at 72 h post inoculation, and TaSOD was induced only at 24 and 48 h compared with the control, when the Pt pathotype THTT was inoculated on a transient expression of Pt9226 in wheat TcLr15. Combining all above, Pt9226 acts as a virulence effector in the interaction between the Pt pathotype THTT and wheat.

Wheat leaf rust fungus is an obligate parasitic fungus that can absorb nutrients from its host plant through haustoria and secrete effector proteins into host cells. The effector proteins are crucial factors for pathogenesis as well as targets for host disease resistance protein recognition. Exploring the role of effector proteins in the pathogenic process of Puccinia triticina Eriks. (Pt) is of great significance for unraveling its pathogenic mechanisms. We previously found that a cysteine-rich effector protein, Pt1641, is highly expressed during the interaction between wheat and Pt, but its specific role in pathogenesis remains unclear. Therefore, this study employed techniques such as heterologous expression, qRT-PCR analysis, and host-induced gene silencing (HIGS) to investigate the role of Pt1641 in the pathogenic process of Pt. The results indicate that Pt1641 is an effector protein with a secretory function and can inhibit BAX-induced programmed cell death in Nicotiana benthamiana. qRT-PCR analyses showed that expression levels of Pt1641 were different during the interaction between the high-virulence strain THTT and low-virulence strains FGD and Thatcher, respectively. The highest expression level in the low-virulence strain FGD was four times that of the high-virulence strain THTT. The overexpression of Pt1641 in wheat near-isogenic line TcLr1 induced callose deposition and H2O2 production on TcLr1. After silencing Pt1641 in the Pt low-virulence strain FGD on wheat near-isogenic line TcLr1, the pathogenic phenotype of Pt physiological race FGD on TcLr1 changed from “;” to “3”, indicating that Pt1641 plays a non-toxic function in the pathogenicity of FGD to TcLr1. This study helps to reveal the pathogenic mechanism of wheat leaf rust and provides important guidance for the mining and application of Pt avirulent genes.

Wheat leaf rust, caused by the obligate biotrophic fungus Puccinia triticina Eriks. (Pt), is one of the most common wheat foliar diseases that continuously threatens global wheat production. Currently, the approaches used to mitigate pathogen infestation include the application of fungicides and the deployment of resistance genes or cultivars. However, the continuous deployment of selected resistant varieties causes host selection pressures that drive Pt evolution and promote the incessant emergence of new virulent races, resulting in the demise of wheat-resistant cultivars after several years of planting. Intriguingly, diploid wheat accessions were found to confer haustorium formation-based resistance to leaf rust, which involves prehaustorial and posthaustorial resistance mechanisms. The prehaustorial resistance in the interaction between einkorn and wheat leaf rust is not influenced by specific races of the pathogen. The induced defense mechanism, known as systemic acquired resistance, also confers durable resistance against a wide array of pathogens. This review summarizes the host range, pathogenic profile, and evolutionary basis of Pt; the molecular basis underlying wheat–Pt interactions; the cloning and characterization of wheat leaf rust resistance genes; prehaustorial and posthaustorial resistance; systemic acquired resistance; and the role of reactive oxygen species. The interplay between climatic factors, genetic features, planting dates, and disease dynamics in imparting resistance is also discussed.

Wheat leaf rust, caused by Puccinia triticina Eriks. (Pt), is a global wheat disease threatening wheat production. Dissecting how Pt effector proteins interact with wheat has great significance in understanding the pathogenicity mechanisms of Pt. In the study, the cDNA of Pt 13-5-72 interacting with susceptible cultivar Thatcher was used as template to amplify Pt13024 gene. The expression pattern and structure of Pt13024 were analyzed by qRT-PCR and online softwares. The secretion function of Pt13024 signal peptide was verified by the yeast system. Subcellular localization of Pt13024 was analyzed using transient expression on Nicotiana benthamiana. The verification that Pt13024 inhibited programmed cell death (PCD) was conducted on N. benthamiana and wheat. The deletion mutation of Pt13024 was used to identify the virulence function motif. The transient transformation of wheat mediated by the type III secretion system (TTSS) was used to analyze the activity of regulating the host defense response of Pt13024. Pt13024 gene silencing was performed by host-induced gene silencing (HIGS). The results showed that Pt13024 was identified as an effector and localized in the cytoplasm and nucleus on the N. benthamiana. It can inhibit PCD induced by the Bcl-2-associated X protein (BAX) from mice and infestans 1 (INF1) from Phytophthora infestans on N. benthamiana, and it can also inhibit PCD induced by DC3000 on wheat. The amino acids 22 to 41 at N-terminal of the Pt13024 are essential for the inhibition of programmed cell death (PCD) induced by BAX. The accumulation of reactive oxygen species and deposition of callose in near-isogenic line TcLr30, which is in Thatcher background with Lr30, induced by Pt13024 was higher than that in 41 wheat leaf rust-resistant near-isogenic lines (monogenic lines) with different resistance genes and Thatcher. Silencing of Pt13024 reduced the leaf rust resistance of Lr30 during the interaction between Pt and TcLr30. We can conclude that Pt13024 is avirulent to TcLr30 when Pt interacts with TcLr30. These findings lay the foundation for further investigations into the role of Pt effector proteins in pathogenesis and their regulatory mechanisms.

ABC transporters play important roles in plant growth and resistance to abiotic and biotic stresses. Here, we showed that the TaABCG36 gene positively regulates leaf rust resistance in the wheat line Thatcher + Lr19 (TcLr19) when challenged with an avirulent pathotype of Puccinia triticina (Pt). The TaABCG36 gene was cloned from genomic DNA and cDNA from wheat line TcLr19. The clone was 6730 bp in gDNA and 4365 bp in cDNA for this gene. It encoded an ABC transporter with 1454 amino acids in length. BLASTp analysis indicated a considerable identity ABC transporter G family member 36 with Aegilops tauschii subsp. strangulata, Triticum dicoccoides, and T. aestivum; thus, we named the gene TaABCG36. TaABCG36 was proved to be a plasma transmembrane protein by bioinformatic analysis and subcellular localization of the TaABCG36–GFP fusion protein. The expression of TaABCG36 in wheat leaves reached a peak at 72 h post-inoculation by Pt avirulence pathotype, and the expression was also induced by phytohormone treatments of salicylic acid (SA), abscisic acid (ABA), and methyl jasmonate (MeJA). Three fragments (V1–V3) of the TaABCG36 gene were introduced to the BSMV-VIGS vector and, thus, silenced the expression of TaABCG36 in the wheat line TcLr19. All the three BSMV:VIGS-infected plants showed reaction type “3” to Pt pathotype THTS, which was fully avirulent on TcLr19 (infection type “0”). Histopathological observation showed that silencing of TaABCG36 facilitated the formation of haustorial mother cells (HMC) and mycelial growth, implying that TaABCG36 plays a positive role in the response of TcLr19 against THTS. These results provide molecular insight into the interaction between Pt and its wheat host and identify a potential target for engineering resistance in wheat to damaging pathogen of Pt.

Wheat leaf rust caused by Puccinia triticina is one of the most common and serious diseases in wheat production. The constantly changing pathogens overcome the plant resistance to P. triticina. Plant pathogens secrete effector proteins that alter the structure of the host cell, interfere plant defenses, or modify the physiology of plant cells. Therefore, the identification of effector proteins is critical to reveal the pathogenic mechanism. We used SignalP v4.1, TargetP v1.1, TMHMM v2.0, and EffectorP v2.0 to screen the candidate effector proteins in P. triticina isolates – KHTT, JHKT, and THSN. As a result, a total of 635 candidate effector proteins were obtained. Structural analysis showed that effector proteins were small in size (50AA to 422AA) and of diverse sequences, and the conserved sequential elements or clear common elements were not involved, regardless of their secretion from the pathogen to the host. There were 427 candidate effector proteins that contain more than or equal to 4 cysteine residues, and 339 candidate effector proteins contained the known motifs. Sixteen families, 9 domains, and 53 other known functional types were found in 186 candidate effector proteins using the Pfam search. Three novel motifs were found by MEME. Heterogeneous expression system was performed to verify the functions of 30 candidate effectors by inhibiting the programmed cell death (PCD) induced by BAX (the mouse-apoptotic gene elicitor) on Nicotiana benthamiana. Hypersensitive response (HR) can be induced by the six effectors in the wheat leaf rust resistance near isogenic lines, and this would be shown by the method of transient expression through Agrobacterium tumefaciens infiltration. The quantitative reverse transcription PCR (qRT-PCR) analysis of 14 candidate effector proteins secreted after P. triticina inoculation showed that the tested effectors displayed different expression patterns in different stages, suggesting that they may be involved in the wheat–P. triticina interaction. The results showed that the prediction of P. triticina effector proteins based on transcriptomic analysis and multiple bioinformatics software is effective and more accurate, laying the foundation of revealing the pathogenic mechanism of Pt and controlling disease.

Wheat cultivar Een1, 34 near isogenic lines (NILs), and two cultivars were used as plant materials to evaluate the resistance of Een1 to leaf rust disease. Infection type identification and gene postulation were carried out by inoculation of 12 Chinese Puccinia triticina (Pt) pathotypes. Based on the unique phenotype of Een1, we speculated that Een1 might carry Lr gene(s) different from the tested ones. The chromosomal locations for resistance gene to leaf rust disease was employed using SSR primers mapping the populations derived from the cross between Een1 and susceptible Thatcher. A total of 285 plants in the F2 population were tested by inoculating Pt pathotype FHNQ during the seedling stage. Results from the segregation analysis fits a ratio of 3:1 ( ${\chi }_{3:1}^{2}=2.37$ χ 3 : 1 2 = 2 . 37 , P = 0.12), indicating the presence of a single dominant gene in Een1 conferring resistance to FHNQ. A total of 1,255 simple sequence repeat (SSR) primers were first used to identify the likely linked markers based on bulk segregation analysis (BSA), and then those likely linked markers were further genotyped in the F2 population for linkage analysis. Our linkage analysis found that the resistance gene (LrE1) was distal to seven SSR loci on the long arm of chromosome 7B, with distances from 2.6 cM (Xgwm344) to 27.1 cM (Xgwm131). The closest marker Xgwm344 was further verified with F3 lines.

Wheat leaf rust (Puccinia triticina) is one of the most important plant diseases in the world, and growing resistant cultivars is the most economical, effective and environmentally safe method for controlling this disease. With the aim of evaluating leaf rust resistance, 10 uncharacterized wheat genotypes, as well as 35 lines with known leaf rust resistance genes (Lr genes), were exposed to 12 Chinese P. triticina pathotypes at both seedling and adult stages. Two wheat genotypes, 09p205 and 09p200, showed high resistance to all the tested pathotypes at both seedling and adult stages. Three accessions, Xinmai 16, 00-225-2-1-2-2, and 21941-6, showed resistance at the adult stage. Four genotypes, 21898-3, 21924-4, 21915-3, and 21982-1, showed slow rusting resistance. In addition, 24 molecular markers were used to assess the presence of 20 known Lr genes. In the 10 genotypes analyzed Lr2c, Lr3ka, Lr9, Lr14a, Lr26, Lr34, and Lr37 were detected, either alone or in combination. [ABSTRACT FROM AUTHOR]

Wheat leaf rust, caused by Puccinia triticina ( Pt ), is one of the most severe fungal diseases on wheat globally. Rational utilization of wheat leaf rust resistance ( Lr ) genes is still the best choice for control this disease. Wheat seedlings carrying Lr19 showed a high resistance phenotype to all Pt races in China. So far, all the cloned seedling Lr genes including Lr1 , Lr10 and Lr21 , encode protein with NBS-LRR domain. In this study, a wheat gene with NBS-LRR domain from previously established Lr19 -resistance-related cDNA library was cloned and designated as TaRGA19 . Full length of this gene was amplified by rapid amplification of cDNA ends (RACE). By blast against IWGSC wheat genome database, we have noticed that TaRGA19 was located on chromosome 2DS, which was different from Lr19 located on chromosome 7DL. Compared with susceptible Thatcher line, expression level of TaRGA19 was upregulated in wheat isogenic lines carrying Lr19 (TcLr19) after inoculation of Pt race THTS. By particle bombardment, TaRGA19-GFP fused protein was localized on plasma membrane of epidermal cells. Using virus-induced gene silencing (VIGS), TaRGA19 -knockdown plants of TcLr19 showed reduced resistance and few sporulation phenotype upon Pt challenge. Further histological observation indicated that Pt hyphal growth at the infection sites was less suppressed in the TaRGA19 -knockdown plants. In conclusion, we speculate this TaRGA19 gene was involved in the Lr19- mediated resistance to wheat leaf rust along with other components. [ABSTRACT FROM AUTHOR]