Abstract
Medicago sativa (also known as alfalfa), a forage legume, is widely cultivated due to its high yield and high-value hay crop production. Infectious diseases are a major threat to the crops, owing to huge economic losses to the agriculture industry, worldwide. The protein-protein interactions (PPIs) between the pathogens and their hosts play a critical role in understanding the molecular basis of pathogenesis. Pseudomonas syringae pv. syringae ALF3 suppresses the plant’s innate immune response by secreting type III effector proteins into the host cell, causing bacterial stem blight in alfalfa. The alfalfa-P. syringae system has little information available for PPIs. Thus, to understand the infection mechanism, we elucidated the genome-scale host-pathogen interactions (HPIs) between alfalfa and P. syringae using two computational approaches: interolog-based and domain-based method. A total of ∼14 M putative PPIs were predicted between 50,629 alfalfa proteins and 2,932 P. syringae proteins by combining these approaches. Additionally, ∼0.7 M consensus PPIs were also predicted. The functional analysis revealed that P. syringae proteins are highly involved in nucleotide binding activity (GO:0000166), intracellular organelle (GO:0043229), and translation (GO:0006412) while alfalfa proteins are involved in cellular response to chemical stimulus (GO:0070887), oxidoreductase activity (GO:0016614), and Golgi apparatus (GO:0005794). According to subcellular localization predictions, most of the pathogen proteins targeted host proteins within the cytoplasm and nucleus. In addition, we discovered a slew of new virulence effectors in the predicted HPIs. The current research describes an integrated approach for deciphering genome-scale host-pathogen PPIs between alfalfa and P. syringae, allowing the researchers to better understand the pathogen’s infection mechanism and develop pathogen-resistant lines.
Highlights
Alfalfa (Medicago sativa L.) or lucerne, a member of the Fabaceae family, is a common forage legume in the United States and other countries
Scientists discovered that the disease-causing strain of P. syringae is a weak pathogen of crops such as sugar beet and snap bean, and a few genes that are unique to the alfalfa pathogen have been identified (Li Q. et al, 2012; Proud sponsor of Midwest Forage Association, 2017)
Since there were a high number of predicted protein-protein interactions (PPIs), we considered the consensus predictions of both approaches, which reduces the chances of false-positive host-pathogen interactions (HPIs)
Summary
Alfalfa (Medicago sativa L.) or lucerne, a member of the Fabaceae family, is a common forage legume in the United States and other countries. Syringae, a ubiquitous epiphyte, is a major disease-causing pathogen in a wide variety of cultivated plant species. It is a rod-shaped gramnegative bacterium with a well-sequenced genome. The outer membrane (Lindow et al, 1989) of P. syringae is surrounded by a unique protein, icenucleation protein (INP), that mimics the crystalline structure of ice and serves as an initiator for ice formation, linking bacterial stem blight to frost This protein is of high interest to the researchers because of its pathogenicity, and because of its other potential applications such as frozen food preparation and snowmaking. We assume that the predicted virulence factors described in this study will serve as a solid foundation for future experimental validations and provide a deeper understanding of pathogen infection in alfalfa
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