Pseudomonas syringae pv. tomato DC3000 induces defense responses in diverse maize inbred lines

Authors: Jaiswal, Namrata; Helm, Matthew

Submitted to: PhytoFrontiers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2024
Publication Date: 5/15/2024
Citation: Jaiswal, N., Helm, M.D. 2024. Pseudomonas syringae pv. tomato DC3000 induces defense responses in diverse maize inbred lines. PhytoFrontiers. https://doi.org/10.1094/PHYTOFR-11-23-0149-SC.
DOI: https://doi.org/10.1094/PHYTOFR-11-23-0149-SC

Interpretive Summary: Maize (corn) has a sophisticated and complex immune system capable of detecting and conferring resistance to plant pathogens. Within the corn immune system, resistance proteins recognize plant pathogens and, upon such recognition, activate a strong immune response, culminating in robust resistance responses against the pathogen. During the infection process, however, plant pathogens often use highly evolved, specialized proteins to “shut-off” the plant immune system, thereby promoting pathogen growth and disease. One such plant pathogen is the bacterium Pseudomonas syringae. In this study, we show that corn detects and mounts a robust defense response against this bacterial pathogen. The results from our work will assist in further understanding how the corn immune system is activates by a plant pathogen and opens the door for bioengineering resistance against corn pathogens.

Technical Abstract: Many phytopathogens translocate virulence (effector) proteins into plant cells to circumvent host immune responses during infection. One such pathogen is Pseudomonas syringae pv. tomato DC3000, which secretes at least thirty-six effectors into host cells, of which a subset elicit host defense responses in crop plant species such as wheat. However, it is unknown whether P. syringae pv. tomato DC3000 is capable of activating immune responses in maize inbreds. We, therefore, screened a diverse maize germplasm collection for effector-dependent recognition of this bacterial pathogen. As a control, we infiltrated Pseudomonas syringae DC3000(D36E), a derivative of P. syringae pv. tomato DC3000 that lacks all endogenous effectors. In our evaluations, we observed a variety of responses to P. syringae pv. tomato DC3000 in maize and scored the phenotypes as either no observable response (N) or as one of three responses: weak chlorosis (WC), chlorosis (C) with minimal cell death, and hypersensitive reaction (HR)-like cell death. Of the twenty-six maize inbreds screened, 13 were scored as N, 2 as WC, 2 as C, and 9 as HR-like cell death. Importantly, no maize line responded to P. syringae DC3000(D36E), demonstrating the phenotypic responses observed are likely dependent upon recognition of one or more P. syringae effectors. Consistent with the phenotypic responses, maize inbred lines that recognize P. syringae pv. tomato DC3000 accumulated detectable hydrogen peroxide within the infiltrated regions as well as an increase in transcript expression of a subset of maize defense genes. Collectively, our results reveal P. syringae induces defense responses in diverse maize inbreds. Our results, therefore, suggest that diverse maize inbred lines likely encode disease resistance proteins that recognize the activities of one or more P. syringae pv. tomato DC3000 effectors.