The results from the analysis indicated that the Arabidopsis homologs of the maize memory genes displayed a wide spectrum of responses including conserved and non-conserved memory responses, but homologs that lack memory or were not involved in the first dehydration stress response were the largest categories.
In a stark contrast with the large number of chloroplast and thylakoid membrane memory genes in Arabidopsis, only four chloroplast and two thylakoid membrane genes display memory genes in maize and none of the conserved or memory genes between the two species encodes a chloroplast/thylakoid membrane-related function (Table 2; Figure 6; Additional files 6 and 7).
In addition, homologous genes display memory responses that are of different transcription memory types in the two species.
memory genes for MYB2, MYB112, MYB13, MYB47, ATHB-7, ATHB-14, and ABF2 specifically cluster with ABA/abiotic stress responding genes but are rarely found among other hormonally responsive pathways; six putative TF genes display memory type responses and only three are shared with other response pathways.
This behavior, consistent with dehydration stress memory, allowed us to address the question of whether maize genes display transcriptional memory in a subsequent dehydration stress.
Finally, we show that memory effect and transcriptionally responsive genes display a major difference in their promoter chromatin structure, with memory effect gene promoters retaining low nucleosome occupancy in abf1 ts yeast while Abf1 binding sites of transcriptionally responsive promoters become occupied by nucleosomes.
Accordingly, these 1,963 genes display dehydration stress transcriptional memory (Table 1; Additional file 4: Table S4).
These genes display modest overlap with genes identified in GWA studies of dependence on addictive substances and memory.These results support polygenic genetics for success in abstaining from smoking, overlap with genetics of substance dependence and memory, and nominate gene variants for selective influences on therapeutic responses to bupropion vs NRT.
Three genes display this response.
Furthermore, although a smaller number of genes is implicated in the dehydration response in maize, the 816 genes displaying memory behavior constitute almost 40% of the entire Z. mays fraction responding in S1, while memory genes constitute ~30% of the dehydration response fraction of A. thaliana (Table 1).
