AbstractPlants are sedentary organisms that constantly sense changes in their environment and react to various environmental cues. On a short-time scale, plants respond through alterations in their physiology, and on a long-time scale, plants alter their development and pass on the memory of stress to the progeny. The latter is controlled genetically and epigenetically and allows the progeny to be primed for future stress encounters, thus increasing the likelihood of survival. The current study intended to explore the effects of multigenerational heat stress in Arabidopsis thaliana. 25 generations of Arabidopsis (Col-0: 15d8) were propagated in the presence of heat stress. The stressed lineages F2H (the 2nd generation of the stressed progeny) and F25H (the 25th generation of the stressed progeny) have been studied to determine their response to heat stress at the stage of plant germination and maturity. Both the F2H and F25H stressed progenies did not show any significant differences from their parallel non-stressed progenies (F2C and F25C) at the germination stage but exhibited a higher tolerance at the mature-plant stage. Both stressed progenies exhibited the elevated frequency of homologous recombination (HR) as compared to their parallel control progenies. A comparison of genomic sequences revealed that F25H lineage had a three-fold higher number of mutations (SNPs and INDELs) as compared to the parallel (F25C) and parental (F2C) lineages, suggesting that heat stress induced genetic variations in the heat-stressed progeny. The F25H stressed progeny showed a 7-fold higher number of non-synonymous mutations than the parental non-stress line which might lead to biological variations subjected to natural selection at the microevolution level. Gene Ontology Analysis revealed that SNPs were enriched mostly in unknown biological processes in all lineages, although processes such as response to stress and stimulus were enriched in the stressed lineage. However, the stressed lineage was underrepresented in the developmental processes, protein metabolism, cell organization, and biogenesis. Methylome analysis revealed that the F25H stressed progeny showed a lower global methylation in the CHH context than the control progenies which suggest that the reduction of methylation in the CHH (p < 0.05) context might be a part of adaptation strategies to heat stress. The F25H lineage was different from the parental control lineage F2C by 66,491 differentially methylated positions (DMPs), but surprisingly, the parallel control (F25C) showed 80,464 DMPs compared to the parental control lineage, indicating that epigenetic variations were likely spontaneous in nature. The differentially methylated regions were enriched mostly in genes related to transcription and DNA dependent processes and DNA or RNA metabolism. Hierarchical clustering of these epimutations separated the heat stressed and control parental progenies into distinct groups which revealed the non-random nature of epimutations. Overall, our study showed that progenies derived from multigenerational heat stress displayed a notable stress memory in context to phenotypic, genotypic and epigenotypic resilience.
Primary carbohydrate metabolism genes participate in heat stress memory at the shoot apical meristem of Arabidopsis thaliana
