A confounding effect of bacterial titer in a type III delivery-based assay of eukaryotic effector function

Authors: CARTER, MORGAN - Cornell University; BOGDANOVE, ADAM - Cornell University; INNES, ROGER - Indiana University; Wise, Roger

Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Research Technical Update
Publication Acceptance Date: 5/14/2018
Publication Date: 5/16/2018
Citation: Carter, M., Bogdanove, A., Innes, R., Wise, R.P. 2018. A confounding effect of bacterial titer in a type III delivery-based assay of eukaryotic effector function. Molecular Plant-Microbe Interactions. 31(11):1115-1116. https://doi.org/10.1094/MPMI-05-18-0128-LE.
DOI: https://doi.org/10.1094/MPMI-05-18-0128-LE

Interpretive Summary:

Technical Abstract: Powdery mildews infect over 9,500 plant species, causing critical yield loss. Powdery mildew disease of barley is caused by the Ascomycete fungus, Blumeria graminis f. sp. hordei (Bgh) and has become a model for the interactions among obligate biotrophs and their cereal hosts. Delivery by bacterial type III secretion is a powerful and increasingly commonly used approach for screening fungal and other eukaryotic candidate effectors in planta (Yin and Hulbert, 2010; Sharma et al., 2013; Upadhyaya et al., 2013; Ittig et al., 2015), especially those of genetically intractable organisms like obligate biotrophs. We used such an approach in Whigham et al., 2015, Broadly Conserved Fungal Effector BEC1019 Suppresses Host Cell Death and Enhances Pathogen Virulence in Powdery Mildew of Barley (Hordeum vulgare L.) (Mol Plant Microbe Interact. 28(9):968-83, doi: 10.1094/MPMI-02-15-0027-FI). In revisiting some of the results of that study, however, a new investigator in our group discovered a confounding effect of the titer of the bacterium that we had not controlled for, rendering some of the experimental results presented in the paper inconclusive. We are writing this letter to provide details, including a tabulation of affected and unaffected figures and conclusions in the paper, and a brief reflection on potential pitfalls to bear in mind when designing experiments that use a bacterial type III secretion-based delivery assay to characterize eukaryotic effectors. Knowledge from this research will impact how plant breeders select for disease resistance, one of the most important traits that affect crop yield, and thus food security.