Engineering chromatin to encode transcriptional immune memory in Arabidopsis

Transcriptional memory is a mechanism that allows organisms to respond more swiftly to repeated stressors. In the case of Arabidopsis thaliana, a specific bacterial immune elicitor known as flg22 induces this type of memory response in certain genes. A study revealed that memory genes exhibit a preference for tissue-specific expression patterns rather than uniform spatial expression.

In their resting state, these memory genes display a distinct chromatin architecture compared to genes that do not exhibit memory. This includes a depletion of H3K4me3, an elevation of H3K27me3, and in some cases, a bivalent marking with both H3K27me3 and H3K4me3. The enzyme JMJ14 plays a crucial role in transcriptional memory, as its occupancy is found to be enriched at memory gene loci.

Upon the priming of these genes, chromatin undergoes reconfiguration, with H3K4me3 levels increasing steadily at memory gene loci. To further investigate the function of this H3K4me3 accumulation, researchers employed epigenome-engineering techniques. This involved the targeted deposition of H3K4me3 at memory gene loci, including the WRKY29 locus.

The results showed that this manipulation was sufficient to drive transcriptional memory and enhance plants' resistance to the bacterial pathogen Pseudomonas syringae. The findings demonstrate that H3K4me3 plays a causal role in transcriptional memory, mediated by JMJ14, and suggest a potential method for enhancing organismal resilience through the rational rewriting of chromatin.