The wheat Snn7 gene confers susceptibility upon recognition of the Parastagonospora nodorum necrotrophic effector SnTox7

Authors: SHI, GONGJUN - North Dakota State University; Friesen, Timothy; SAINI, JYOTI - North Dakota State University; Xu, Steven; RASMUSSEN, JACK - North Dakota State University; Faris, Justin

Submitted to: The Plant Genome
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/18/2015
Publication Date: 7/10/2015
Publication URL: http://handle.nal.usda.gov/10113/62627
Citation: Shi, G., Friesen, T.L., Jyoti Saini, Xu, S.S., Rasmussen, J.B., Faris, J.D. 2015. The wheat Snn7 gene confers susceptibility on recognition of the Parastagonospora nodorum necrotrophic effector SnTox7. The Plant Genome. 8. doi: 10.3835/plantgenome2015.02.0007.

Interpretive Summary: The wheat disease known as Septoria nodorum blotch (SNB) is caused by a necrotophic fungus and leads to significant yield losses. Necrotrophic fungi differ from biotrophic fungi in that they kill the host tissue and live and feed on the dead tissue, whereas biotrophic fungi require living host tissue on which to live and feed. Much is known about how plants defend themselves against biotrophic pathogens, but interactions between plants and necrtrophic pathogens are less understood. However, in recent years research has shown that necrtrophic pathogens such as the fungus that causes SNB produce small proteins that are recognized by specific genes in wheat, and when a specific fungal protein is recognized by a specific wheat gene, the plant triggers the death of its own tissue allowing the pathogen to live, feed, and proliferate. This research describes the discovery and characterization of a new pathogen protein (SnTox7) and wheat gene (Snn7) involved in this system. Like other fungal protein-wheat gene pairs reported so far, the Snn7-SnTox7 interaction leads to cell death and ultimately disease. This work yields additional knowledge of how necrotrophic fungi cause disease in plants, and molecular markers generated in this work will aid breeders in selecting wheat lines lacking the Snn7 gene to improve resistance to SNB.

Technical Abstract: Parastagonospora nodorum is a necrotrophic fungal pathogen that causes the disease Septoria nodorum blotch (SNB) on wheat. The fungus produces necrotrophic effectors (NEs), that when recognized by corresponding host genes, cause cell death, which ultimately leads to disease. To date, eight host gene-NE interactions have been described in the wheat-P. nodorum system. Here, we report the identification and partial characterization of a ninth interaction involving a P. nodorum-produced NE designated SnTox7 and a wheat gene designated Snn7. SnTox7 is small protein with estimated size less than 30 kDa and largely resistant to heat and chemical treatment. The Snn7 gene governs sensitivity to SnTox7 and was delineated to a 2.7 cM interval on the long arm of wheat chromosome 2D. The Snn7-SnTox7 interaction explained 33% of the variation in disease among 406 segregating F2 plants indicating the interaction plays a prominent role in the development of SNB. The Snn7 sensitivity allele was identified in the hexaploid wheat cultivar Timstein, but evaluation of a set of 52 hexaploid of diverse origin indicated that few genotypes harbored a functional Snn7 allele, thus indicating that Snn7 is relatively rare. The identification of the Snn7-SnTox7 interaction adds to our knowledge of the wheat-P. nodorum pathosystem, which is becoming a model for necrotrophic specialist fungal pathogens and their interactions with plants leading to necrtrophic effector-triggered susceptibility (NETS).