Figure 5.

Induction, duration, and phenotypic manifestation of conifer epigenetic memory. Memory can be induced by various stimuli, such as temperature, phytohormones, and insect attack (black arrows). A) Climatic memory induced during embryogenesis is known to be very long-term (>20 years) (green forms). Different kinds of climatic stimuli may result in different epitypes being induced from a single genotype (epitype 1 to 3). These epitypes have different phenologies that may remain altered for the rest of the plants’ life. B) Biotic stress memory is manifested phenotypically in response to a triggering stimulus such as an insect attack (white arrows), seems to be attenuated over time (<4 years) (dark orange forms), and is manifested more short-term (bell-shaped curves) than climatic memory. There are still many unknowns about conifer epigenetic memory. For example, does induction during embryogenesis result in a more long-term memory resembling the climatic memory (light orange form)? Is epigenetic memory in conifers trans-generational (hashed green and orange forms)? Are there interactions between climatic and biotic stress memory?