Antimicrobial Peptides as Part of the Arsenal of Constitutive and Inducible Seed Defences in Tomato Seed Exudates Against Pathogens

Seed immune responses are an underexplored area in host-pathogen interactions, leaving seed-pathogen interactions poorly understood despite their considerable economic impact. This study examined tomato seed defences by assessing the antimicrobial activity (AA) of seed exudates during germination. Results showed genotype-dependent and constitutive defence responses from seeds showing AA in exudates. Seed priming with a panel of elicitors such as methyl jasmonate (MeJA) enhanced AA in certain genotypes, highlighting an inducible defence response. Both constitutive and inducible (elicitor-dependent) seed defences were genotype-dependent and more effective against the non-host pathogen Alternaria brassicicola (Abra43), while host pathogens seemed resistant to exudates' AA, suggesting that they developed strategies to neutralise exudates' AA. Multi-omic analyses revealed distinct hormonal and molecular pathways involved in constitutive and inducible defences. By characterising exudates and correlating genotype- and elicitor-specific AA, candidate antimicrobial compounds were identified. As proof of concept, we functionally validated the AA of a putative defensin (Solyc07g007755) whose expression was highly correlated with the observed AA of the seed exudate against Abra43, demonstrating the potential of our dataset for the development of phytosanitary strategies to protect seeds during germination.