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Title: Brachypodium distachyon-Cochliobolus sativus pathosystem is a new model for studying plant-fungal interactions in cereal crops

Author
item ZHONG, SHIAOBIN - North Dakota State University
item ALI, SHAUKAT - North Dakota State University
item LENG, YUEQIANG - North Dakota State University
item WANG, RUI - North Dakota State University
item Garvin, David

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/16/2014
Publication Date: 4/1/2015
Publication URL: http://handle.nal.usda.gov/10113/61143
Citation: Zhong, S., Ali, S., Leng, Y., Wang, R., Garvin, D.F. 2015. Brachypodium distachyon-Cochliobolus sativus pathosystem is a new model for studying plant-fungal interactions in cereal crops. Phytopathology. 105:482-489.

Interpretive Summary: Diseases cause large yield losses in small grain crops. One fungal pathogen that causes damage to both wheat and barley is Cochliobolus sativus. Natural variation for resistance to C. sativus has allowed scientists to develop resistant crop varieties, but the resistance genes do not protect against all of the genetically different isolates of the pathogen. Further, the molecular basis of resistance to the pathogen has not been unraveled, in part due to the complex genomes of wheat and barley. The model grass Brachypodium distachyon, with its small genome and rapid life cycle, can serve as a surrogate for wheat and barley to explore how grasses interact with pathogens. In this study, research was undertaken to determine whether Brachypodium can serve as a host for C. sativus, to explore whether there is genetic variation for resistance in Brachypodium, and lastly to examine the genetic basis of resistance variation in Brachypodium. Results indicate that Brachypodium is infected by C. sativus in a manner similar to what has been observed in barley and wheat, and develops disease symptoms that are also comparable to what is observed on these crops. Genetic variation for resistance to C. sativus was found in Brachypodium, with resistance varying depending on the C. sativus isolate used, similar to what is observed in wheat and barley. Examination of an F2 population of Brachypodium from a cross between two lines that exhibit variation in resistance indicates that resistance is governed by a single gene. Given the simple genome and genome resources for Brachypodium, it will be possible to isolate this resistance gene, and this will provide a new tool to accelerate molecular dissection of resistance mechanisms. This information will lead to new strategies for developing resistance to C. sativus in wheat and barley, which in turn will increase yield and quality of these important grain crops and increase farm profits.

Technical Abstract: Cochliobolus sativus (anamorph: Bipolaris sorokiniana) causes three major diseases in barley and wheat, including spot blotch, common root rot and kernel blight or black point. These diseases significantly reduce the yield and quality of the two most important cereal crops in the US and other regions of the world. However, little is known about the molecular mechanisms underlying the pathogenicity and host specificity of the fungal pathogen as well as resistance or susceptibility of the hosts. This study aims to investigate the host status of the grass model plant Brachypodium distachyon to C. sativus and establish the B. distachyon – C. sativus interaction as a new model pathosystem for studying plant-fungal interactions in cereal crops. Six diploid B. distachyon lines (Bd1-1, Bd21, Bd21-3, Bd2-3, Bd3-1 and Bd18-1) were inoculated with five C. sativus strains (ND93-1, ND90Pr, ND85F, ND4008 and Cs07-47-1) that exhibited different virulence patterns on barley and wheat differential lines. The results indicated that all six B. distachyon lines were infected by the C. sativus strains and their susceptibility varied depending on the C. sativus strains used. A wide range of responses from a hypersensitive response (HR)-mediated resistance to full susceptibility were also observed in a large collection of B. distachyon accessions with diverse background when inoculated with four of the C. sativis isolate (ND90Pr, ND85F, ND4008 and Cs07-47-1). Genetic analysis of a F2 population derived from the cross between Bd1-1 and Bd3-1, which showed differential infection responses to Cs07-47-1, suggests that the resistance to C. sativus is controlled by major genes in B. distachyon. The availability of whole genome sequences of both the host (B. distachyon) and the pathogen (C. sativus) makes the pathosystem an attractive model for studying diseases in cereal crops.