Benzothiadiazole conditions the bean proteome for immunity to bean rust

Authors: Cooper, Bret; Beard, Hunter; Garrett, Wesley; Campbell, Kimberly

Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2020
Publication Date: 3/2/2020
Citation: Cooper, B., Beard, H.S., Garrett, W.M., Campbell, K. 2020. Benzothiadiazole conditions the bean proteome for immunity to bean rust. Molecular Plant-Microbe Interactions. https://doi.org/10.1094/MPMI-09-19-0250-R.
DOI: https://doi.org/10.1094/MPMI-09-19-0250-R

Interpretive Summary: Common bean rust, caused by a fungus, reduces harvests of the dry, edible common bean and reduces food security for the people who rely on beans for a primary source of nutrition. Natural resistance genes in the plant can provide protection until a strain of the fungus that breaks resistance emerges. In this study, we demonstrate that a chemical called benzothiadiazole (BTH) can be sprayed on susceptible beans to induce resistance to common bean rust. Plants sprayed with BTH showed no signs of disease 10 days after inoculation with rust spores while plants without BTH sustained heavy infections and died. To better understand the effect BTH has on the bean leaf, we measured proteins using mass spectrometry, an analytical technique. Proteins that increased accumulation included receptor-like kinases that perceive pathogens and signal downstream defense pathways. There were increases for more than 100 other proteins that likely contributed to resistance. These included enzymes that catalyze phenylpropanoid biosynthetic pathways that lead to the production of lignin that makes leaf cell walls stronger against fungal penetration and to the production of phytoalexins that are toxic to fungi. These results will be of interest to scientists in the government, at universities, and at private institutions who are interested in using BTH to protect beans from rusts by amplifying the bean plant’s natural immune system.

Technical Abstract: Common bean rust, caused by the fungus Uromyces appendiculatus, reduces harvests of the dry, edible common bean and reduces food security for the people who rely on beans for a primary source of nutrition. Natural resistance genes in the plant can provide protection until a strain of the fungus that breaks resistance emerges. In this study, we demonstrate that benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester (BTH) can be sprayed on susceptible beans to induce resistance to common bean rust. Protection occurred as soon as 72 hours after treatment and resulted in no signs of disease 10 days after inoculation with rust spores. By contrast, the susceptible control plants sustained heavy infections and died. To better understand the effect BTH has on the bean proteome, we measured the changes of accumulation for 3,973 proteins using mass spectrometry and Tandem Mass Tag methodology. The set of 409 proteins with significantly increased accumulation in BTH-treated leaves included receptor-like kinases SOBIR1, CERK1, and LYK5 that perceive pathogens and transmit a signal through EDS1, a regulator of the salicylic acid defense pathway. More than 100 other proteins likely contributed to resistance including PR-proteins, a full complement of enzymes that catalyze phenylpropanoid biosynthesis, and protein receptors, transporters, and enzymes that modulate other defense responses controlled by jasmonic acid, ethylene, brassinosteroid, abscisic acid, and auxin. Increases in the accumulation of proteins required for vesicle mediated protein secretion and RNA splicing occurred as well. By contrast, more than half of the 168 decreases belonged to chloroplast proteins and proteins involved in cell expansion. These results provide a detailed picture of the proteomic changes in beans after BTH application, reveal a set of proteins needed for rust resistance, and reaffirm the utility of BTH to control disease by amplifying the bean plant’s natural immune system.