Plant synthetic epigenomic engineering for crop improvement.

Efforts have been directed to redesign crops with increased yield, stress adaptability, and nutritional value through synthetic biology-the application of engineering principles to biology. A recent expansion in our understanding of how epigenetic mechanisms regulate plant development and stress responses has unveiled a new set of resources that can be harnessed to develop improved crops, thus heralding the promise of "synthetic epigenetics." In this review, we summarize the latest advances in epigenetic regulation and highlight how innovative sequencing techniques, epigenetic editing, and deep learning-driven predictive tools can rapidly extend these insights. We also proposed the future directions of synthetic epigenetics for the development of engineered smart crops that can actively monitor and respond to internal and external cues throughout their life cycles.

Genome-edited ATP BINDING CASSETTE B1 transporter SD8 knockouts show optimized rice architecture without yield penalty.

This study reports the identification of the rice open reading frame Semi-Dwarf in chr8 (SD8) that encodes a putative ortholog of Arabidopsis thaliana ABCB1. Genome editing of SD8 leads to optimized rice architecture by reducing plant height and flag-leaf angle without yield penalty. Rice SD8 knockouts may also have the potential for increased yield under high density planting.

A deep learning approach to automate whole-genome prediction of diverse epigenomic modifications in plants.

Epigenetic modifications function in gene transcription, RNA metabolism, and other biological processes. However, multiple factors currently limit the scientific utility of epigenomic datasets generated for plants. Here, using deep-learning approaches, we developed a Smart Model for Epigenetics in Plants (SMEP) to predict six types of epigenomic modifications: DNA 5-methylcytosine (5mC) and N6-methyladenosine (6mA) methylation, RNA N6-methyladenosine (m6 A) methylation, and three types of histone modification. Using the datasets from the japonica rice Nipponbare, SMEP achieved 95% prediction accuracy for 6mA, and also achieved around 80% for 5mC, m6 A, and the three types of histone modification based on the 10-fold cross-validation. Additionally, > 95% of the 6mA peaks detected after a heat-shock treatment were predicted. We also successfully applied the SMEP for examining epigenomic modifications in indica rice 93-11 and even the B73 maize line. Taken together, we show that the deep-learning-enabled SMEP can reliably mine epigenomic datasets from diverse plants to yield actionable insights about epigenomic sites. Thus, our work opens new avenues for the application of predictive tools to facilitate functional research, and will almost certainly increase the efficiency of genome engineering efforts.

Harnessing Current Knowledge of DNA N6-Methyladenosine From Model Plants for Non-model Crops.

Epigenetic modifications alter the gene activity and function by causing change in the chromosomal architecture through DNA methylation/demethylation, or histone modifications without causing any change in DNA sequence. In plants, DNA cytosine methylation (5mC) is vital for various pathways such as, gene regulation, transposon suppression, DNA repair, replication, transcription, and recombination. Thanks to recent advances in high throughput sequencing (HTS) technologies for epigenomic "Big Data" generation, accumulated studies have revealed the occurrence of another novel DNA methylation mark, N6-methyladenosine (6mA), which is highly present on gene bodies mainly activates gene expression in model plants such as eudicot Arabidopsis (Arabidopsis thaliana) and monocot rice (Oryza sativa). However, in non-model crops, the occurrence and importance of 6mA remains largely less known, with only limited reports in few species, such as Rosaceae (wild strawberry), and soybean (Glycine max). Given the aforementioned vital roles of 6mA in plants, hereinafter, we summarize the latest advances of DNA 6mA modification, and investigate the historical, known and vital functions of 6mA in plants. We also consider advanced artificial-intelligence biotechnologies that improve extraction and prediction of 6mA concepts. In this Review, we discuss the potential challenges that may hinder exploitation of 6mA, and give future goals of 6mA from model plants to non-model crops.

Rice and Arabidopsis homologs of yeast CHROMOSOME TRANSMISSION FIDELITY PROTEIN 4 commonly interact with Polycomb complexes but exert divergent regulatory functions.

Both genetic and epigenetic information must be transferred from mother to daughter cells during cell division. The mechanisms through which information about chromatin states and epigenetic marks like histone 3 lysine 27 trimethylation (H3K27me3) are transferred have been characterized in animals; these processes are less well understood in plants. Here, based on characterization of a dwarf rice (Oryza sativa) mutant (dwarf-related wd40 protein 1, drw1) deficient for yeast CTF4 (CHROMOSOME TRANSMISSION FIDELITY PROTEIN 4), we discovered that CTF4 orthologs in plants use common cellular machinery yet accomplish divergent functional outcomes. Specifically, drw1 exhibited no flowering-related phenotypes (as in the putatively orthologous Arabidopsis thaliana eol1 mutant), but displayed cell cycle arrest and DNA damage responses. Mechanistically, we demonstrate that DRW1 sustains normal cell cycle progression by modulating the expression of cell cycle inhibitors KIP-RELATED PROTEIN 1 (KRP1) and KRP5, and show that these effects are mediated by DRW1 binding their promoters and increasing H3K27me3 levels. Thus, although CTF4 orthologs ENHANCER OF LHP1 1 (EOL1) in Arabidopsis and DRW1 in rice are both expressed uniquely in dividing cells, commonly interact with several Polycomb complex subunits, and promote H3K27me3 deposition, we now know that their regulatory functions diverged substantially during plant evolution. Moreover, our work experimentally illustrates specific targets of CTF4/EOL1/DRW1, their protein-proteininteraction partners, and their chromatin/epigenetic effects in plants.

Reorganization of the 3D chromatin architecture of rice genomes during heat stress.

BACKGROUND: The three-dimensional spatial organization of the genome plays important roles in chromatin accessibility and gene expression in multiple biological processes and has been reported to be altered in response to environmental stress. However, the functional changes in spatial genome organization during environmental changes in crop plants are poorly understood. RESULTS: Here we perform Hi-C, ATAC-seq, and RNA-seq in two agronomically important rice cultivars, Nipponbare (Nip; Japonica) and 93-11 (Indica), to report a comprehensive profile of nuclear dynamics during heat stress (HS). We show that heat stress affects different levels of chromosome organization, including A/B compartment transition, increase in the size of topologically associated domains, and loss of short-range interactions. The chromatin architectural changes were associated with chromatin accessibility and gene expression changes. Comparative analysis revealed that 93-11 exhibited more dynamic gene expression and chromatin accessibility changes, including HS-related genes, consistent with observed higher HS tolerance in this cultivar. CONCLUSIONS: Our data uncovered higher-order chromatin architecture as a new layer in understanding transcriptional regulation in response to heat stress in rice.

Transcriptional landscape of rice roots at the single-cell resolution.

There are two main types of root systems in flowering plants, namely taproot systems of dicots and fibrous root systems found in monocots. Despite this fundamental split, our current knowledge of cellular and molecular mechanism driving root development is mainly based on studies of the dicot model Arabidopsis. However, the world major crops are monocots and little is known about the transcriptional programs underlying cell-type specification in this clade. Here, we report the transcriptomes of more than 20 000 single cells derived from root tips of two agronomically important rice cultivars. Using combined computational and experimental analyses we were able to robustly identify most of the major cell types and define novel cell-type-specific marker genes for both cultivars. Importantly, we found divergent cell types associated with specific regulatory programs, including phytohormone biosynthesis, signaling, and response, which were well conserved between the two rice cultivars. In addition, we detected substantial differences between the cell-type transcript profiles of Arabidopsis and rice. These species-specific features emphasize the importance of analyzing tissues across diverse model species, including rice. Taken together, our study provides insight into the transcriptomic landscape of major cell types of rice root tip at single-cell resolution and opens new avenues to study cell-type specification, function, and evolution in plants.

PRMT6 physically associates with nuclear factor Y to regulate photoperiodic flowering in Arabidopsis.

The timing of floral transition is critical for reproductive success in flowering plants. In long-day (LD) plant Arabidopsis, the floral regulator gene FLOWERING LOCUS T (FT) is a major component of the mobile florigen. FT expression is rhythmically activated by CONSTANS (CO), and specifically accumulated at dusk of LDs. However, the underlying mechanism of adequate regulation of FT transcription in response to day-length cues to warrant flowering time still remains to be investigated. Here, we identify a homolog of human protein arginine methyltransferases 6 (HsPRMT6) in Arabidopsis, and confirm AtPRMT6 physically interacts with three positive regulators of flowering Nuclear Factors YC3 (NF-YC3), NF-YC9, and NF-YB3. Further investigations find that AtPRMT6 and its encoding protein accumulate at dusk of LDs. PRMT6-mediated H3R2me2a modification enhances the promotion of NF-YCs on FT transcription in response to inductive LD signals. Moreover, AtPRMT6 and its homologues proteins AtPRMT4a and AtPRMT4b coordinately inhibit the expression of FLOWERING LOCUS C, a suppressor of FT. Taken together, our study reveals the role of arginine methylation in photoperiodic pathway and how the PRMT6-mediating H3R2me2a system interacts with NF-CO module to dynamically control FT expression and facilitate flowering time. Supplementary Information: The online version contains supplementary material available at 10.1007/s42994-021-00065-y.

RNA 5-Methylcytosine Controls Plant Development and Environmental Adaptation.

Despite increasing understanding of 5-methylcytosine (m5C) on RNAs in mammals, the function of m5C in plants remains obscure. A dynamic function of m5C in plant development and stress adaptation had been suggested, and Tang et al. have now uncovered a role for RNA m5C methyltransferase in rice adaptation to high temperature.

Mesostigma viride Genome and Transcriptome Provide Insights into the Origin and Evolution of Streptophyta.

The Streptophyta include unicellular and multicellular charophyte green algae and land plants. Colonization of the terrestrial habitat by land plants is a major evolutionary event that has transformed the planet. So far, lack of genome information on unicellular charophyte algae hinders the understanding of the origin and the evolution from unicellular to multicellular life in Streptophyta. This work reports the high-quality reference genome and transcriptome of Mesostigma viride, a single-celled charophyte alga with a position at the base of Streptophyta. There are abundant segmental duplications and transposable elements in M. viride, which contribute to a relatively large genome with high gene content compared to other algae and early diverging land plants. This work identifies the origin of genetic tools that multicellular Streptophyta have inherited and key genetic innovations required for the evolution of land plants from unicellular aquatic ancestors. The findings shed light on the age-old questions of the evolution of multicellularity and the origin of land plants.

N6-Methyladenine DNA Methylation in Japonica and Indica Rice Genomes and Its Association with Gene Expression, Plant Development, and Stress Responses.

N6-Methyladenine (6mA) DNA methylation has recently been implicated as a potential new epigenetic marker in eukaryotes, including the dicot model Arabidopsis thaliana. However, the conservation and divergence of 6mA distribution patterns and functions in plants remain elusive. Here we report high-quality 6mA methylomes at single-nucleotide resolution in rice based on substantially improved genome sequences of two rice cultivars, Nipponbare (Nip; Japonica) and 93-11 (Indica). Analysis of 6mA genomic distribution and its association with transcription suggest that 6mA distribution and function is rather conserved between rice and Arabidopsis. We found that 6mA levels are positively correlated with the expression of key stress-related genes, which may be responsible for the difference in stress tolerance between Nip and 93-11. Moreover, we showed that mutations in DDM1 cause defects in plant growth and decreased 6mA level. Our results reveal that 6mA is a conserved DNA modification that is positively associated with gene expression and contributes to key agronomic traits in plants.