Host susceptibility factors render ripe tomato fruit vulnerable to fungal disease despite active immune responses

• Published in: Journal of experimental botany Vol. 72; no. 7; pp. 2696 - 2709
• Main Authors: Silva, Christian J, van den Abeele, Casper, Ortega-Salazar, Isabel, Papin, Victor, Adaskaveg, Jaclyn A, Wang, Duoduo, Casteel, Clare L, Seymour, Graham B, Blanco-Ulate, Barbara
• Format: Journal Article
• Language: English
• Published: UK Oxford University Press 29.03.2021
• Subjects: Botrytis; Fruit - immunology; Fruit - microbiology; Gene Expression Regulation, Plant; Lycopersicon esculentum - genetics; Lycopersicon esculentum - immunology; Lycopersicon esculentum - microbiology; Plant Diseases - immunology; Plant Diseases - microbiology; Plant Immunity; Plant Proteins - genetics; Plant Proteins - metabolism; Research Papers; pectate lyase; preformed defenses; susceptibility factors; fruit–pathogen interactions; non-ripening mutants; fruit ripening; immune responses; Botrytis cinerea; Rhizopus stolonifer; Fusarium acuminatum
• ISSN: 0022-0957; 1460-2431; 1460-2431
• DOI: 10.1093/jxb/eraa601

Abstract The increased susceptibility of ripe fruit to fungal pathogens poses a substantial threat to crop production and marketability. Here, we coupled transcriptomic analyses with mutant studies to uncover critical processes associated with defense and susceptibility in tomato (Solanum lycopersicum) fruit. Using unripe and ripe fruit inoculated with three fungal pathogens, we identified common pathogen responses reliant on chitinases, WRKY transcription factors, and reactive oxygen species detoxification. We established that the magnitude and diversity of defense responses do not significantly impact the interaction outcome, as susceptible ripe fruit mounted a strong immune response to pathogen infection. Then, to distinguish features of ripening that may be responsible for susceptibility, we utilized non-ripening tomato mutants that displayed different susceptibility patterns to fungal infection. Based on transcriptional and hormone profiling, susceptible tomato genotypes had losses in the maintenance of cellular redox homeostasis, while jasmonic acid accumulation and signaling coincided with defense activation in resistant fruit. We identified and validated a susceptibility factor, pectate lyase (PL). CRISPR-based knockouts of PL, but not polygalacturonase (PG2a), reduced susceptibility of ripe fruit by >50%. This study suggests that targeting specific genes that promote susceptibility is a viable strategy to improve the resistance of tomato fruit against fungal disease. Increased susceptibility to fungal disease during tomato ripening is driven by the accumulation of susceptibility factors, particularly a pectin degrading enzyme.