Elevated transcription of transposable elements is accompanied by het-siRNA-driven de novo DNA methylation in grapevine embryogenic callus

Insights into plant regeneration: cellular pathways and DNA methylation dynamics

Plants, known for their immobility, employ various mechanisms against stress and damage. A prominent feature is the formation of callus tissue-a cellular growth phenomenon that remains insufficiently explored, despite its distinctive cellular plasticity compared to vertebrates. Callus formation involves dedifferentiated cells, with a subset attaining pluripotency. Calluses exhibit an extraordinary capacity to reinitiate cellular division and undergo structural transformations, generating de novo shoots and roots, thereby developing into regenerated plants-a testament to the heightened developmental plasticity inherent in plants. In this way, plant regeneration through clonal propagation is a widely employed technique for vegetative reproduction. Thus, exploration of the biological components involved in regaining pluripotency contributes to the foundation upon which methods of somatic plant propagation can be advanced. This review provides an overview of the cellular pathway involved in callus and subsequent de novo shoot formation from already differentiated plant tissue, highlighting key genes critical to this process. In addition, it explores the intricate realm of epigenetic regulatory processes, emphasizing the nuanced dynamics of DNA methylation that contribute to plant regeneration. Finally, we briefly discuss somaclonal variation, examining its relation to DNA methylation, and investigating the heritability of epigenomic changes in crops.

Assessing small RNA profiles in potato diploid hybrid and its resynthesized allopolyploid reveals conserved abundance with distinct genomic distribution

KEY MESSAGE

The shock produced by the allopolyploidization process on a potato interspecific diploid hybrid displays a non-random remobilization of the small RNAs profile on a variety of genomic features. Allopolyploidy, a complex process involving interspecific hybridization and whole genome duplication, significantly impacts plant evolution, leading to the emergence of novel phenotypes. Polyploids often present phenotypic nuances that enhance adaptability, enabling them to compete better and occasionally to colonize new habitats. Whole-genome duplication represents a genomic "shock" that can trigger genetic and epigenetic changes that yield novel expression patterns. In this work, we investigate the polyploidization effect on a diploid interspecific hybrid obtained through the cross between the cultivated potato Solanum tuberosum and the wild potato Solanum kurtzianum, by assessing the small RNAs (sRNAs) profile of the parental diploid hybrid and its derived allopolyploid. Small RNAs are key components of the epigenetic mechanisms involved in silencing by RNA-directed DNA Methylation (RdDM). A sRNA sequencing (sRNA-Seq) analysis was performed to individually profile the 21 to 22 nucleotide (21 to 22-nt) and 24-nt sRNA size classes due to their unique mechanism of biogenesis and mode of function. The composition and distribution of different genomic features and differentially accumulated (DA) sRNAs were evaluated throughout the potato genome. We selected a subset of genes associated with DA sRNAs for messenger RNA (mRNA) expression analysis to assess potential impacts on the transcriptome. Interestingly, we noted that 24-nt DA sRNAs that exclusively mapped to exons were correlated with differentially expressed mRNAs between genotypes, while this behavior was not observed when 24-nt DA sRNAs were mapped to intronic regions. These findings collectively emphasize the nonstochastic nature of sRNA remobilization in response to the genomic shock induced by allopolyploidization.

Emerging Roles of Epigenetics in Grapevine and Winegrowing

Epigenetics refers to dynamic chemical modifications to the genome that can perpetuate gene activity without changes in the DNA sequence. Epigenetic mechanisms play important roles in growth and development. They may also drive plant adaptation to adverse environmental conditions by buffering environmental variation. Grapevine is an important perennial fruit crop cultivated worldwide, but mostly in temperate zones with hot and dry summers. The decrease in rainfall and the rise in temperature due to climate change, along with the expansion of pests and diseases, constitute serious threats to the sustainability of winegrowing. Ongoing research shows that epigenetic modifications are key regulators of important grapevine developmental processes, including berry growth and ripening. Variations in epigenetic modifications driven by genotype-environment interplay may also lead to novel phenotypes in response to environmental cues, a phenomenon called phenotypic plasticity. Here, we summarize the recent advances in the emerging field of grapevine epigenetics. We primarily highlight the impact of epigenetics to grapevine stress responses and acquisition of stress tolerance. We further discuss how epigenetics may affect winegrowing and also shape the quality of wine.

Comprehensive analysis of both long and short read transcriptomes of a clonal and a seed-propagated model species reveal the prerequisites for transcriptional activation of autonomous and non-autonomous transposons in plants

Background

Transposable element (TE) transcription is a precursor to its mobilisation in host genomes. However, the characteristics of expressed TE loci, the identification of self-competent transposon loci contributing to new insertions, and the genomic conditions permitting their mobilisation remain largely unknown.

Results

Using Vitis vinifera embryogenic callus, we explored the impact of biotic stressors on transposon transcription through the exposure of the callus to live cultures of an endemic grapevine yeast, Hanseniaspora uvarum. We found that only 1.7–2.5% of total annotated TE loci were transcribed, of which 5–10% of these were full-length, and the expressed TE loci exhibited a strong location bias towards expressed genes. These trends in transposon transcription were also observed in RNA-seq data from Arabidopsis thaliana wild-type plants but not in epigenetically compromised Arabidopsis ddm1 mutants. Moreover, differentially expressed TE loci in the grapevine tended to share expression patterns with co-localised differentially expressed genes. Utilising nanopore cDNA sequencing, we found a strong correlation between the inclusion of intronic TEs in gene transcripts and the presence of premature termination codons in these transcripts. Finally, we identified low levels of full-length transcripts deriving from structurally intact TE loci in the grapevine model.

Conclusion

Our observations in two disparate plant models representing clonally and seed propagated plant species reveal a closely connected transcriptional relationship between TEs and co-localised genes, particularly when epigenetic silencing is not compromised. We found that the stress treatment alone was insufficient to induce large-scale full-length transcription from structurally intact TE loci, a necessity for non-autonomous and autonomous mobilisation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13100-022-00271-5.