Mechanisms of stress memories in plants

This 2016 Australian review’s subject was plant memory mechanisms:

“Plants are adept at rapidly acclimating to stressful conditions and are able to further fortify their defenses by retaining memories of stress to enable stronger or more rapid responses should an environmental perturbation recur.

The recovery process entails a balancing act between resetting and memory formation. During recovery, RNA metabolism, posttranscriptional gene silencing, and RNA-directed DNA methylation have the potential to play key roles in resetting the epigenome and transcriptome and in altering memory.”

Many of the principles applied to animals, and several animal studies were cited for illustration. Here’s one of the graphics:

F6.large


I disagreed with the Summary statement:

“Memory, in particular epigenetic memory, is likely a relatively rare event.”

The reviewers cited a 2015 Australian study Stress induced gene expression drives transient DNA methylation changes at adjacent repetitive elements which found the opposite conclusion with rice:

“Despite 21 days of starvation, resupplying phosphate for just 1 day reversed expression of 40% of induced genes, further increasing to 80% after 3 days and corresponding with a reestablished internal root phosphate concentration. Interestingly though, 80 genes remained differentially regulated even after 31 days of resupply.”

The study’s researchers attributed their epigenetic memory finding to several factors, including their study design:

“The majority of DNA methylation analyses performed in plants to date have focused on Arabidopsis, despite being relatively depleted of TEs [transposable elements] (15–20% of the genome) and being poorly methylated compared to other plant genomes.

To date, only a limited number of studies have comprehensively investigated the involvement of DNA methylation in response to adverse environmental conditions. Several studies have reported that changes in the environment can affect the methylation status of some regions of the genome, using low resolution and non-quantitative techniques. These studies have lacked the resolution to provide the specific context and genomic location of the changes in DNA methylation, thus offering limited insights into the potential role of stress-induced changes in DNA methylation.”

So the reviewers judging “memory, in particular epigenetic memory” to be “a relatively rare event” probably had more to do with study designs rather than what actually occurs in nature.

http://advances.sciencemag.org/content/2/2/e1501340.full “Reconsidering plant memory: Intersections between stress recovery, RNA turnover, and epigenetics”

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One thought on “Mechanisms of stress memories in plants

  1. https://www.researchgate.net/publication/295241375_Reconsidering_plant_memory_Intersections_between_stress_recovery_RNA_turnover_and_epigenetics#211527

    Hi Paul,
    Thanks for the comment. I agree that study design plays a big role in scientific discovery. Also agree that there are some great examples of epigenetic memory and that the role of TEs and requisite epigenetic influences are going to be more relevant in plants with more TEs (maize comes to mind).

    If anything; however, I’d wager that there would be ascertainment bias in favour of the importance of epigenetic memory and adaptive traits vs resetting, forgetting or lack of memory. Of course ‘rare’ is also a subjective term. Ultimately, the main point of the article was to turn people’s minds to the other side of the coin from memory. There are likely processes to reset and/or circumvent memory formation and these warrant further investigation. If plants used epigenetic mechanisms to store memories of all their encounters with adverse environments, they would likely become bamboozled and accumulate maladaptive traits inhibiting growth and proliferation; hence the hypothesis that memories are relatively ‘rare’.

    cheers

    Like

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