Microscopic and Molecular Characterization of the Prehaustorial Resistance against Wheat Leaf Rust (Puccinia triticina) in Einkorn (Triticum monococcum)

Abstract

Puccinia triticina f. sp. tritici (Eriks.), the causal agent of leaf rust, causes substantial yield losses in wheat production. In wheat many major leaf rust resistance genes have been overcome by virulent races. In contrast, the prehaustorial resistance (phr) against wheat leaf rust detected in the diploid wheat Einkorn (Triticum monoccocum var. monococcum) accession PI272560 confers race-independent resistance against isolates virulent on accessions harboring resistance genes located on the A-genome of Triticum aestivum. Phr in PI272560 leads to abortion of fungal development during the formation of haustorial mother cells and to increased hydrogen peroxide concentration in comparison to the susceptible accession 36554 (Triticum boeoticum ssp. thaoudar var. reuteri). Increased peroxidase and endochitinase activity was detected in PI272560 within 6 h after inoculation (hai). Comparative transcriptome profiling using Massive Analysis of cDNA Ends (MACE) in infected and non-infected leaves detected 14220 differentially expressed tags in PI272560 and 15472 in accession 36554. Of these 2908 and 3004, respectively, could be assigned to Gene Ontology (GO) categories of which 463 were detected in both accessions and 311 were differentially expressed between the accessions. In accordance with the concept of non-host resistance in PI272560, genes with similarity to peroxidases, chitinases, β-1,3-glucanases and other pathogenesis-related genes were up-regulated within the first 8 hai, whereas up-regulation of such genes was delayed in 36554. Moreover, a Phosphoribulokinase gene contributing to non-host resistance in rice against stripe rust was exclusively expressed in the resistant accession PI272560. Gene expression underpinned physiological and phenotypic observations at the site of infection and are in accordance with the concept of non-host resistance.

Histopathological aspects of induced resistance byPseudomonas protegensCHA0 and β-aminobutyric acid in wheat againstPuccinia triticina

“…This suggests that H 2 O 2 might initiate HR-defence mechanism. Our results are in line with the observation of Serfling et al (2016) where HR was observed in mesophyll cells that were in contact with fungal haustorial mother cells at 24 hai, and the observed pre-haustorial resistance in the resistant accession PI272560 is due to an early HR of the first infected mesophyll cells. An HR accompanied by H 2 O 2 accumulation also occurs in other interactions of plants with fungal parasites and causes non-host resistance to wheat stripe rust in broad bean (Cheng et al 2012).…”

“…This could explain that accumulation of H 2 O 2 in guard cells following recognition of leaf rust structures might be involved in stomatal closure, this being supported by the fact that we observed more accumulation of ABA in plants infected with leaf rust (data no shown), It had been reported that appressoria formation of P. triticina also caused stomata closure in wheat leaves (Bolton et al 2008). Further studies shoe a correlation between H 2 O 2 generation and hypersensitive reaction (HR) in resistance mechanism against wheat rust species (Wang et al 2007; Orczyk et al 2010; Serfling et al 2016). In the current study, the accumulation of H 2 O 2 due to both resistance inducers was observed 24 hai which corresponds to the beginning of haustorium generation.…”

“…Primed plants recognize the pathogen and produce reactive oxygen species (ROS) and deposit callose at the infection sites (Balmer et al 2015). This rapid local oxydative burst generates, among other, hydrogen peroxide (H 2 O 2 ) during pre-haustorial resistance against wheat leaf rust caused by P. triticina (Wesp-Guterres et al 2013; Serfling et al 2016). Callose is an effective barrier that is induced at the sites of attack during the early stages of pathogen invasion (Luna et al 2011).…”

Exploring and exploiting the boundaries of host specificity using the cereal rust and mildew models

“…This very early detection response of nonself in plants is known as PAMPtriggered immunity (PTI) and is best characterized in model organisms such as rice and Arabidopsis (Meyers et al, 2003;Zhou et al, 2004;Chinchilla et al, 2006;Zipfel, 2008;Ayliffe et al, 2011). Pre-haustorial resistance (PHR) is where fungal growth is terminated before plant cell entry and has proven more durable against biotrophic pathogens (Rubiales & Niks, 1996;Mart ınez et al, 2001;Serfling et al, 2016). PHR led to macroscopic immunity in previous studies in wheat (Anker & Niks, 2001;Serfling et al, 2016) and barley (Hoogkamp et al, 1998;Dracatos et al, 2014Dracatos et al, , 2016, and is a feature of host, near nonhost and nonhost interactions.…”

“…Pre-haustorial resistance (PHR) is where fungal growth is terminated before plant cell entry and has proven more durable against biotrophic pathogens (Rubiales & Niks, 1996;Mart ınez et al, 2001;Serfling et al, 2016). PHR led to macroscopic immunity in previous studies in wheat (Anker & Niks, 2001;Serfling et al, 2016) and barley (Hoogkamp et al, 1998;Dracatos et al, 2014Dracatos et al, , 2016, and is a feature of host, near nonhost and nonhost interactions. The best and most widely studied examples of such resistance are mutant or naturally defective alleles of the Mlo locus in barley (Tosa & Shishiyama, 1984).…”