TRANSCRIPTIONAL MEMORY AND TRANSGENERATIONAL INHERITANCE OF STRESS

As sessile organisms, plants must be able to quickly modulate their gene expression to deal with changes in the environment. Under extreme conditions such as drought or heat stress, plants modulate their gene expression through targeted changes to many genes resulting in the ability to withstand these conditions. After return to stable environmental conditions, normal gene expression programs are restored. Subsequent exposure to stress induces some genes to exhibit transcriptional memory which is characterized as directional or intensity changes in the expression of a gene when comparing across multiple repetitive stresses. The mechanisms that facilitate transcriptional memory in plants are unclear some evidence suggests that epigenetic pathways are involved. If this feature is controlled epigenetically, is it possible that some of this information is transmitted to subsequent generations? In rice, plants exposed to 11 subsequent generations of simulated drought stress showed directional changes in DNA methylation and changes in gene expression compared to the first generation under drought stress. These changes were also correlated to physiological changes associated with improved dehydration tolerance (Zheng et al., 2017). I suspect that targeted modification of gene expression is responsible for stress priming and the changes in regulation and DNA methylation over generations in a manner that fine tunes the response to stress. In plants, RNA-directed DNA methylation is a major epigenetic regulation pathway that uses 24-nt siRNA to target enzymes to specific loci for DNA methylation and chromatin modification.  Targets of RdDM are enriched in transposable elements nearby genes. Mutants of RdDM misregulate the expression of many genes including some involved in stress response. The goal of this work is to investigate the role of RdDM in transcriptional memory and transgenerational epigenetic inheritance of severe drought exposure in maize.