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1. Regulatory Divergence in Wound-Responsive Gene Expression between Domesticated and Wild Tomato

   https://doi.org/10.1105/tpc.18.00194  

   Ming-Jung Liu, Koichi Sugimoto (May 2018, The Plant cell)

   The evolution of transcriptional regulatory mechanisms is central to how stress response and tolerance differ between species. However, it remains largely unknown how divergence in cis-regulatory sites and, subsequently, transcription factor (TF) binding specificity contribute to stress-responsive expression divergence, particularly between wild and domesticated spe-cies. By profiling wound-responsive gene transcriptomes in wild Solanum pennellii and do-mesticated S. lycopersicum, we found extensive wound-response divergence and identified 493 S. lycopersicum and 278 S. pennellii putative cis-regulatory elements (pCREs) that were predictive of wound-responsive gene expression. Only 24-52% of these wound-response pCREs (depending on wound-response patterns) were consistently enriched in the putative promoter regions of wound-responsive genes across species. In addition, between these two species, their differences in pCRE site sequences were significantly and positively correlated with differences in wound-responsive gene expression. Furthermore, ~11-39% of pCREs were specific to only one of the species and likely bound by TFs from different families. These findings indicate substantial regulatory divergence in these two plant species that di-verged ~3-7 million years ago. Our study provides insights into the mechanistic basis of how the transcriptional response to wounding is regulated and, importantly, the contribution of cis-regulatory components to variation in wound-responsive gene expression between a wild and a domesticated plant species. 

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2. Modeling temporal and hormonal regulation of plant transcriptional response to wounding

   https://doi.org/10.1093/plcell/koab287  

   Moore, Bethany M.; Lee, Yun Sun; Wang, Peipei; Azodi, Christina; Grotewold, Erich; Shiu, Shin-Han (December 2021, The Plant Cell)

   Abstract Plants respond to wounding stress by changing gene expression patterns and inducing the production of hormones including jasmonic acid. This wounding transcriptional response activates specialized metabolism pathways such as the glucosinolate pathways in Arabidopsis thaliana. While the regulatory factors and sequences controlling a subset of wound-response genes are known, it remains unclear how wound response is regulated globally. Here, we how these responses are regulated by incorporating putative cis-regulatory elements, known transcription factor binding sites, in vitro DNA affinity purification sequencing, and DNase I hypersensitive sites to predict genes with different wound-response patterns using machine learning. We observed that regulatory sites and regions of open chromatin differed between genes upregulated at early and late wounding time-points as well as between genes induced by jasmonic acid and those not induced. Expanding on what we currently know, we identified cis-elements that improved model predictions of expression clusters over known binding sites. Using a combination of genome editing, in vitro DNA-binding assays, and transient expression assays using native and mutated cis-regulatory elements, we experimentally validated four of the predicted elements, three of which were not previously known to function in wound-response regulation. Our study provides a global model predictive of wound response and identifies new regulatory sequences important for wounding without requiring prior knowledge of the transcriptional regulators. 

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3. Prediction of conserved and variable heat and cold stress response in maize using cis-regulatory information

   https://doi.org/10.1093/plcell/koab267  

   Zhou, Peng; Enders, Tara A; Myers, Zachary A; Magnusson, Erika; Crisp, Peter A; Noshay, Jaclyn M; Gomez-Cano, Fabio; Liang, Zhikai; Grotewold, Erich; Greenham, Kathleen; et al (November 2021, The Plant Cell)

   Abstract Changes in gene expression are important for responses to abiotic stress. Transcriptome profiling of heat- or cold-stressed maize genotypes identifies many changes in transcript abundance. We used comparisons of expression responses in multiple genotypes to identify alleles with variable responses to heat or cold stress and to distinguish examples of cis- or trans-regulatory variation for stress-responsive expression changes. We used motifs enriched near the transcription start sites (TSSs) for thermal stress-responsive genes to develop predictive models of gene expression responses. Prediction accuracies can be improved by focusing only on motifs within unmethylated regions near the TSS and vary for genes with different dynamic responses to stress. Models trained on expression responses in a single genotype and promoter sequences provided lower performance when applied to other genotypes but this could be improved by using models trained on data from all three genotypes tested. The analysis of genes with cis-regulatory variation provides evidence for structural variants that result in presence/absence of transcription factor binding sites in creating variable responses. This study provides insights into cis-regulatory motifs for heat- and cold-responsive gene expression and defines a framework for developing models to predict expression responses across multiple genotypes. 

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4. Parallel and population-specific gene regulatory evolution in cold-adapted fly populations

   https://doi.org/10.1093/genetics/iyab077  

   Huang, Yuheng; Lack, Justin B; Hoppel, Grant T; Pool, John E (May 2021, Genetics)

   Begun, D (Ed.)

   Abstract Changes in gene regulation at multiple levels may comprise an important share of the molecular changes underlying adaptive evolution in nature. However, few studies have assayed within- and between-population variation in gene regulatory traits at a transcriptomic scale, and therefore inferences about the characteristics of adaptive regulatory changes have been elusive. Here, we assess quantitative trait differentiation in gene expression levels and alternative splicing (intron usage) between three closely related pairs of natural populations of Drosophila melanogaster from contrasting thermal environments that reflect three separate instances of cold tolerance evolution. The cold-adapted populations were known to show population genetic evidence for parallel evolution at the SNP level, and here we find evidence for parallel expression evolution between them, with stronger parallelism at larval and adult stages than for pupae. We also implement a flexible method to estimate cis- vs trans-encoded contributions to expression or splicing differences at the adult stage. The apparent contributions of cis- vs trans-regulation to adaptive evolution vary substantially among population pairs. While two of three population pairs show a greater enrichment of cis-regulatory differences among adaptation candidates, trans-regulatory differences are more likely to be implicated in parallel expression changes between population pairs. Genes with significant cis-effects are enriched for signals of elevated genetic differentiation between cold- and warm-adapted populations, suggesting that they are potential targets of local adaptation. These findings expand our knowledge of adaptive gene regulatory evolution and our ability to make inferences about this important and widespread process. 

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5. mRNA N⁶ ‐methyladenosine is critical for cold tolerance in Arabidopsis

   https://doi.org/10.1111/tpj.15872  

   Govindan, Ganesan; Sharma, Bishwas; Li, Yong‐Fang; Armstrong, Christopher D.; Merum, Pandrangaiah; Rohila, Jai S.; Gregory, Brian D.; Sunkar, Ramanjulu (July 2022, The Plant Journal)

   SUMMARY Plants respond to low temperatures by altering the mRNA abundance of thousands of genes contributing to numerous physiological and metabolic processes that allow them to adapt. At the post‐transcriptional level, these cold stress‐responsive transcripts undergo alternative splicing, microRNA‐mediated regulation and alternative polyadenylation, amongst others. Recently, m⁶A, m⁵C and other mRNA modifications that can affect the regulation and stability of RNA were discovered, thus revealing another layer of post‐transcriptional regulation that plays an important role in modulating gene expression. The importance of m⁶A in plant growth and development has been appreciated, although its significance under stress conditions is still underexplored. To assess the role of m⁶A modifications during cold stress responses, methylated RNA immunoprecipitation sequencing was performed in Arabidopsis seedlings esposed to low temperature stress (4°C) for 24 h. This transcriptome‐wide m⁶A analysis revealed large‐scale shifts in this modification in response to low temperature stress. Because m⁶A is known to affect transcript stability/degradation and translation, we investigated these possibilities. Interestingly, we found that cold‐enriched m⁶A‐containing transcripts demonstrated the largest increases in transcript abundance coupled with increased ribosome occupancy under cold stress. The significance of the m⁶A epitranscriptome on plant cold tolerance was further assessed using themtamutant in which the major m⁶A methyltransferase gene was mutated. Compared to the wild‐type, along with the differences inCBFsandCORgene expression levels, themtamutant exhibited hypersensitivity to cold treatment as determined by primary root growth, biomass, and reactive oxygen species accumulation. Furthermore, and most importantly, both non‐acclimated and cold‐acclimatedmtamutant demonstrated hypersensitivity to freezing tolerance. Taken together, these findings suggest a critical role for the epitranscriptome in cold tolerance of Arabidopsis. 

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