Global warming is an ever-growing threat to ecosystems all over the world. Temperatures are continually rising, and weather patterns have become more irregular and aggressive—making it difficult for all organisms to survive.
Plants are an essential part of our ecosystem, and their survival can benefit from the rising CO2 levels, but severely high temperatures present a larger problem. Since plants can’t adjust to their climates by getting up and moving around, they must internally regulate their response to heat.
Remembering past heat stress response is a survival technique plants use and it’s called “acquired thermotolerance” or heat acclimation. Scientists have been studying it for years, but exactly how this phenomenon works on a molecular level is still unclear.
To understand more about how plants build up thermotolerance, scientists from the Nara Institute of Science and Technology in Japan conducted a study on Arabidopsis thaliana to determine how it regulates itself to intense heat. Specifically, they looked at which epigenetic mechanisms were involved in the activity. Their findings are available in the June issue of Nature Communications.
The process involves a family of histone demethylases called JUMONJI (JMJ). These proteins regulate heat shock genes, allowing the plants to recall how to deal with the extreme temperature increases.
Histone demethylases are enzymes that remove methyl groups from modified histone proteins, which could result in altered gene expression. Both JMJ and other heat shock proteins (HSPs) are consistent in plants and animals and are involved in cell development. HSPs also function in protein stabilization and help maintain homeostasis in the presence of a stressor.
“Heat stress is often repeating and changing,” says Dr. Nobutoshi Yamaguchi—lead author of the study. “Once plants have undergone mild heat stress, they become tolerant and can adapt to further heat stress. This is referred to as heat stress ‘memory’ and has been reported to be correlated to epigenetic modifications.”
To determine the changes in gene activity during heat acclimation, the team grew A.thaliana plants at 22 °C (normal conditions) and exposed them to a heat-shocked at 44°C. They found the genes JMJ30, JMJ32, ELF6, and REF6 consistent in the plants that survived the heat shock, implying that they are necessary for heat acclimation.
To establish how the A.thaliana forms heat memory, they identified regions where gene expression changed due to acclimation. Their results showed that acclimation encourages demethylation of H3K27me3 at two particular heat shock genes: HSP22 and HSP17.6C. These two genes were found to be highly expressed after the plants were exposed to 37 °C for 20 mins, but expression decreased quickly as the plants responded to the temperature.
Further analysis revealed that the acclimated plants remembered the heat exposure for at least 3 days. The team discovered that H3K27me3 was removed from the HSP22 and HSP17.6C genes by the JMJ proteins. This outcome implies that the presence of JMJ proteins helped to generate a faster heat shock response in the acclimated plants by activating HSPs.
Overall, the authors were able to successfully determine that acclimation to extreme temperatures can increase a plant’s thermotolerance. Hopefully, the findings in this study will help future research build upon the understanding of plant response and memory with the hope to improve the heat tolerance in plants and crops threatened by climate change.
Source: Yamaguchi, N., et al. (2021). H3K27me3 demethylases alter HSP22 and HSP17.6C expression in response to recurring heat in Arabidopsis. Nature Communications. 12, 3480
Reference: Nara Institute of Science and Technology. How to beat the heat: Memory mechanism allows plants to adapt to heat stress. NIST Research Achievements. 10 June 2021. Web.
