Heritable Induced Resistance in : Tips and Tools to Improve Effect Size and Reproducibility

Over a decade ago, three independent studies reported that pathogen- and herbivore-exposed produces primed progeny with increased resistance. Since then, heritable induced resistance (h-IR) has been reported across numerous plant-biotic interactions, revealing a regulatory function of DNA (de)methylation dynamics. However, the identity of the epi-alleles controlling h-IR and the mechanisms by which they prime defense genes remain unknown, while the evolutionary significance of the response requires confirmation. Progress has been hampered by the relatively high variability, low effect size, and sometimes poor reproducibility of h-IR, as is exemplified by a recent study that failed to reproduce h-IR in by pv. (). This study aimed to improve h-IR effect size and reproducibility in the - interaction. We show that recurrent inoculations of seedlings result in stronger h-IR than repeated inoculations of older plants and that disease-related growth repression in the parents is a reliable marker for h-IR effect size in F1 progeny. Furthermore, RT-qPCR-based expression profiling of genes controlling DNA methylation maintenance revealed that the elicitation of strong h-IR upon seedling inoculations is marked by reduced expression of the chromatin remodeler DECREASE IN DNA METHYLATION 1 () gene, which is maintained in the apical meristem and transmitted to F1 progeny. Two additional genes, and CHROMOMETHYLASE3 (), displayed similar transcriptional repression in progeny from seedling-inoculated plants. Thus, reduced expression of , , and can serve as a marker of robust h-IR in F1 progeny. Our report offers valuable information and markers to improve the effect size and reproducibility of h-IR in the - model interaction.