Zea mays Transcriptome or Gene expression
Arabidopsis thaliana plants that have experienced an initial exposure to dehydration stress (“trained plants”) have an increased ability to maintain leaf relative water content (RWC) during subsequent stresses than plants experiencing the stress for the first time and transcription of  selected dehydration response genes is altered during successive exposures to dehydration stress. This physiological and transcriptional behavior of trained plants is consistent with a “memory “of an earlier stress. It is unknown whether such memory is present in other Angiosperm lineages and whether it is an evolutionarily conserved response to stress. Here, we analyzed the behavior and transcriptomes of maize (Zea mays) plants experiencing multiple dehydration stresses and compare them with responses of the evolutionarily distant A. thaliana. We found structurally related genes in maize that displayed the same memory-type  responses as in A. thaliana, providing evidence of the conservation of function and transcriptional memory in the evolution of plants' dehydration stress response systems. Similar to A. thaliana, trained Z. mays plants retained higher RWC during dehydration stress than untrained plants, due in part to maintaining reduced stomatal conductance, despite full recovery of RWC, after the first stress. Divergent transcriptional memory responses were also expressed, suggesting diversification of function among stress memory genes. Some dehydration stress memory genes were also shared with other stress and hormone responding pathways, indicating complex and dynamic interactions between different plant signaling networks.   The results provide new insight into how plants respond to multiple dehydration stresses and provide a platform for studies of the functions of memory genes in adaptive responses to water deficit in monocot and eudicot plants .  Overall design: For each condition (water, S1, and S3) the transcriptome was sequenced for two replicates. The watered condition is considered the control.