Priming (also referred to as acclimation, acquired stress resistance, adaptive response, or cross-protection) is defined as an exposure of an organism to mild stress that leads to the development of a subsequent stronger and more protective response. This memory of a previously encountered stress likely provides a strong survival advantage in a rapidly shifting environment. Priming has been identified in animals, plants, fungi, and bacteria.
Figure 1. Priming is defined as a time-limited pre-exposure of an organism to a mild stress that leads to an increased adaptive response to subsequent exposures. (A) If the initial priming stress and the subsequent exposure are of the same nature, they are referred to as cis-priming. (B) If priming and exposure differ, they are termed trans-priming. Mechanisms of priming include differential RNA or protein expression and storage, histone modifications and DNA methylation. (C) Intergenerational priming occurs when the stress memory is observed in the first, stress-free offspring generation, while (D) trans-generational priming is observed after more than two stress-free offspring generations.| Organism | Species | Priming Stress | Exposure Results | Mechanism | References |
|---|---|---|---|---|---|
| Mice | Mus musculus | Infection with sub-lethal concentrations of the pathogenic mold A. fumigatus | 80% survival of primed mice, rapid and severe disease onset which cleared after 3 d | Rapid phagocytosis by neutrophiles, elevated levels of the proinflammatory cytokine IL-17 | [33] |
| Mice | Mus musculus | Vaccinate mice with liposomal L-mannose protein | Higher survival rate of vaccinated mice after re-infection with C. albicans | Elevated production of polyclonal antibodies | [34] |
| Roundworms | Caenorhabditis elegans | Exposure to different stressors: heavy metals, NaCl, fasting. | Increased resistance to fatal oxidative stress which last up to F3 | Induction of the transcription factor SKN1 for the oxidative stress response | [13] |
| Insects | Galleria mellonela | Inoculation with sub lethal doses of the pathogen C.albicans | Protection against lethal doses of re-infection with same pathogen | Upregulation of antifungal genes (e.g., gallerimycin) | [35] |
| Insects | Drosophila Melanogaster | Inoculation with sublethal doses of the Pathogen S. pneumoniae | Protection against lethal doses of re-infection with same pathogen | Higher and efficient phagocytosis | [36] |
| Plants | Arabidopsis thaliana | Exposure to secreted volatiles from a damaged neighboring plant infected with M. separata larva | Protection against future herbivores | Increased Trypsin inhibitors (TI-plant defense genes) by demethylation of the TI promoter | [23] |
| Plants | Arabidopsis thaliana | Mild osmotic stress (50 mM NaCl) |
Higher tolerance to drought stress and extreme osmotic stress (80 mM NaCl) | Histone modification, and increased NaCl transporter (HKT1) induction after second exposure to salt stress | [20] |
| Plants | Arrhenatherum elatius | Dehydration periods of 16 days |
Improved photo-protection and higher biomass in second exposure to severe drought | Not known | [21] |
| Plants | Triticum aestivum (winter wheat) | Moderate drought during the vegetative growth period of the plant | Better tolerance to post-anthesis severe drought | Regulating of hormonal levels (e.g., cytokinnines) | [18] |
| Plants | Soybean seeds |
Low to mild concentrations of melatonin | Increased salt tolerance, increased drought tolerance | Upregulation of several genes involved in photosynthesis and sugar metabolism | [24] |
| Bacteria | Bacillus subtilis | Mild heat shock stress (48 °C for 15 min) | Increased tolerance against lethal heat shock stress (53 °C) | Less protein aggregation | [26] |
| Bacteria | Escherichia coli | Subinhibitory concentrations of the antibiotic Ampicillin | Increased resistance to lethal levels of ampicillin, increased resistance to lethal oxidative stress and heat shock stress. | Upregulation of genes involved in higher energy metabolism and more ribosomal production | [31] |
| Bacteria | Escherichia coli | Sublethal doses of AMPs (pexiganan and melittin) | Increased resistance to lethal doses of AMPs (pexiganan and melittin) | Higher amount of colanic-acid capsule in pexiganan-primed cells. Elevated levels of curli fimbriae in melittin-primed cells | [32] |
| Bacteria | Listeria monocytogenes | Exposure to NaCl stress | Increased resistance to the antimicrobial food preservation molecule Nisin | Increased transcript levels of LiaR-regulated genes | [29] |
| Species | Priming Stress | Exposure Result | Mechanism | References |
|---|---|---|---|---|
| Saccharomyces cerevisiae | Heat stress (37 °C, 1 h) or osmotic stress (0.7 M, 1 h) | Better tolerance to severe heat shock (47 °C) | Induction of GPDH in osmotic stressed cells, but not in heat-shock stressed cells. Mechanism unknown. | [40] |
| Saccharomyces cerevisiae | Exposure to sub-lethal temperatures | Increased thermotolerance | Mechanism involves the ATPase proton pump | [38] |
| Saccharomyces cerevisiae | Oxidative stress (H2O2), sub-lethal ethanol stress, cold stress | Barotolerence or high hydrostatic pressure tolerance (HHP) | Upregulation of genes involved in oxidative stress defense response, cell membrane changes | [45] |
| Saccharomyces cerevisiae | Exposure to several mild stressors (acute heat, NaCl, oxidative stress, ethanol) | Resistance to same stressor * (e.g., p.heat-s.heat), resistance to some subsequent stressors (p.NaCl-s.NaCl and H2O2) | Induction of transcription factors Msn2p and/or Msn4p | [43] |
| Saccharomyces cerevisiae | Salt (NaCl) stress | Tolerance to severe oxidative stress (H2O2) | A role for the nuclear pore component Nup42p | [39] |
| Candida albicans | Mild heat, osmotic or oxidative stress | Heat stressed cells exhibited tolerance to a strong oxidative stress | Slightly increased in HSPs levels (heat shock protein) | [46] |
| Candida albicans | Different concentrations of glucose, low, mild and high | Increased resistance to the antifungal miconazole, increased resistance to osmotic stress and oxidative stress | Upregulation of genes involved in drug resistance, induction of osmotic stress related genes, | [47] |
| Metarhizium anisopliae | Sub-lethal concentrations of heat stress, oxidative stress, osmotic stress and nutritive stress | Increased resistance of p.nutritive and p.oxidative -s.UV-B and s.heat. Increased resistance of p.heat–s.UV-B and heat |
Partially established, increased levels of sugars (trehalose and mannitol) | [48] |
| Agaricus bisporus | Application of exogenous riboflavin/vitamin B2 | Increased drought resistance | Not established, but changes in transcripts levels was observed | [49] |
| Penicillium chrysogenum | Mild drought stress | Increased resistance to severe drought | Higher β-glucosidase and respiratory activity | [50] |
| Rhizopus arrhyzus | Exposure to sub-lethal concentrations of voriconazole or isavuconazole | In vivo hypervirulence observed by lower survival rate of fruit flies (D. melanogaster) | Unknown | [51] |
| Rhizopus arrhyzus | Tornadic shear stress | Hypervirulence in D. melanogaster in vivo model | Secreted metabolites and calcineurin-signaling pathway (not fully characterized) | [52] |
| Aspergillus fumigatus | Mild heat stress (37 or 45 °C) | Increased resistance to both oxidative stress and severe heat stress (60 °C) | Increased sugar content (trehalose) | [53] |
| Aspergillus fumigatus | Different environmental stressors: minimal medium, 50 °C, NaCl, +Fe and -Zn | Increased pathogenicity in D. melanogaster in vivo model | Not established | [54] |
| Aspergillus fumigatus | Osmotic stress (0.5M NaCl or KCl) Zinc-starved stress, cold (4 °C) or heat (42 °C induced stress | Increased tolerance to oxidative stress, or zinc-stress | Multiple changes in genes transcript levels: ZapA (osmotic stress), Hsp70 and ZapA (heat and zinc-starves stress), ergosterol pathway (osmotic stress), gliotoxin secretion (Zinc-starved stress) | [55] |
This entry is adapted from the peer-reviewed paper 10.3390/jof8050448