Genetic and epigenetic modifications to the BBAA component of common wheat during its evolutionary history at the hexaploid level

Noncoding RNA network crosstalk in organ fibrosis

Fibrosis is a process involving excessive accumulation of extracellular matrix components, the severity of which interferes with the function of the organ in question. With the advances in RNA sequencing and in-depth molecular studies, a large number of current studies have pointed out the irreplaceable role of non-coding RNAs (ncRNAs) in the pathophysiological development of organ fibrosis. Here, by summarizing the results of a large number of studies on the interactions between ncRNAs, some studies have found that long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs), among others, are able to act as sponges or decoy decoys for microRNAs (miRNAs), act as competing endogenous RNAs (ceRNAs) to regulate the expression of miRNAs, and subsequently act on different mRNA targets, playing a role in the development of fibrosis in a wide variety of organs, including the heart, liver, kidneys, and spleen. parenchymal organs, including heart, liver, kidney, and spleen, play important roles in the development of fibrosis. These findings elucidate the intricate involvement of the lncRNA/circRNA-miRNA-mRNA axis in the pathophysiological processes underpinning organ fibrosis, thereby enhancing our comprehension of the onset and progression of this condition. Furthermore, they introduce novel potential therapeutic targets within the realm of ncRNA-based therapeutics, offering avenues for the development of innovative drugs aimed at mitigating or reversing the effects of organ fibrosis.

LHP1-mediated epigenetic buffering of subgenome diversity and defense responses confers genome plasticity and adaptability in allopolyploid wheat

Polyploidization is a major driver of genome diversification and environmental adaptation. However, the merger of different genomes may result in genomic conflicts, raising a major question regarding how genetic diversity is interpreted and regulated to enable environmental plasticity. By analyzing the genome-wide binding of 191 trans-factors in allopolyploid wheat, we identified like heterochromatin protein 1 (LHP1) as a master regulator of subgenome-diversified genes. Transcriptomic and epigenomic analyses of LHP1 mutants reveal its role in buffering the expression of subgenome-diversified defense genes by controlling H3K27me3 homeostasis. Stripe rust infection releases latent subgenomic variations by eliminating H3K27me3-related repression. The simultaneous inactivation of LHP1 homoeologs by CRISPR-Cas9 confers robust stripe rust resistance in wheat seedlings. The conditional repression of subgenome-diversified defenses ensures developmental plasticity to external changes, while also promoting neutral-to-non-neutral selection transitions and adaptive evolution. These findings establish an LHP1-mediated buffering system at the intersection of genotypes, environments, and phenotypes in polyploid wheat. Manipulating the epigenetic buffering capacity offers a tool to harness cryptic subgenomic variations for crop improvement.

Chromosome karyotype and stability of new synthetic hexaploid wheat

Synthetic hexaploid wheat offers breeders ready access to potentially novel genetic variation in wild ancestral species. In this study, we crossed MY3478 (2n = 4x = 28, AABB) as the maternal parent with the stripe rust-resistant SY41 (2n = 2x = 14, DD) as the paternal parent to construct the new hexaploid wheat line NA0928 through natural allopolyploidization. Agronomic traits and the cytology of the S8-S9 generations of NA0928 were analyzed. Abundant variation in agronomic traits was observed among each strain of NA0928 in the S8 generation. Agronomic traits were superior in strains resistant to stripe rust compared with those of highly susceptible strains. The rank order of the coefficients of variation were tiller number (55.3%) > spike length (15.3%) > number of spikelets (13.9%) > plant height (8.7). Number of tillers and spike length are important traits in wheat breeding to improve yield. Cytological observation and fluorescence in situ hybridization showed that the chromosome number and configuration showed rich variation among NA0928 strains in the S9 generation. Chromosome number ranged from 36 to 44. Variation in chromosome karyotype was detected in the A and B subgenomes. Meiotic chromosome behavior in pollen mother cells and multicolor genomic in situ hybridization revealed that two new synthetic hexaploid wheat strains showed genetic stability; one strain was resistant to stripe rust and developed multiple tillers, and the other strain was susceptible to stripe rust, but both showed improved thousand-kernel weight (TKW) weight and produced multiple tillers. The two strains will be valuable germplasm resources for use in wheat breeding.

Dynamic and reversible DNA methylation changes induced by genome separation and merger of polyploid wheat

Background

Wheat is a powerful genetic model for studying polyploid evolution and crop domestication. Hexaploid bread wheat was formed by two rounds of interspecific hybridization and polyploidization, processes which are often accompanied by genetic and epigenetic changes, including DNA methylation. However, the extent and effect of such changes during wheat evolution, particularly from tetraploid-to-hexaploid wheat, are currently elusive.

Results

Here we report genome-wide DNA methylation landscapes in extracted tetraploid wheat (ETW, AABB), natural hexaploid wheat (NHW, AABBDD), resynthesized hexaploid wheat (RHW, AABBDD), natural tetraploid wheat (NTW, AABB), and diploid (DD). In the endosperm, levels of DNA methylation, especially in CHG (H=A, T, or C) context, were dramatically decreased in the ETW relative to natural hexaploid wheat; hypo-differentially methylated regions (DMRs) (850,832) were 24-fold more than hyper-DMRs (35,111). Interestingly, those demethylated regions in ETW were remethylated in the resynthesized hexaploid wheat after the addition of the D genome. In ETW, hypo-DMRs correlated with gene expression, and TEs were demethylated and activated, which could be silenced in the hexaploid wheat. In NHW, groups of TEs were dispersed in genic regions of three subgenomes, which may regulate the expression of TE-associated genes. Further, hypo-DMRs in ETW were associated with reduced H3K9me2 levels and increased expression of histone variant genes, suggesting concerted epigenetic changes after separation from the hexaploid.

Conclusion

Genome merger and separation provoke dynamic and reversible changes in chromatin and DNA methylation. These changes correlate with altered gene expression and TE activity, which may provide insights into polyploid genome and wheat evolution.

The Capacity to Buffer and Sustain Imbalanced D-Subgenome Chromosomes by the BBAA Component of Hexaploid Wheat Is an Evolved Dominant Trait

Successful generation of pentaploid wheat (genome, BBAAD) via interspecific hybridization between tetraploid wheat (BBAA) and hexaploid wheat (BBAADD) holds great promise to mutually exchange desirable traits between the two cultivated wheat species, as well as providing a novel facet for evolutionary studies of polyploid wheat. Taking advantage of the viable and fertile nature of an extracted tetraploid wheat (ETW) with a BBAA genome that is virtually identical with the BBAA component of a hexaploid common wheat, and a synthetic hexaploid wheat, we constructed four pentaploid wheats with several distinct yet complementary features, of which harboring homozygous BBAA subgenomes is a common feature. By using a combined FISH/GISH method that enables diagnosing all individual wheat chromosomes, we precisely karyotyped a larger number of cohorts from the immediate progenies of each of the four pentaploid wheats. We found that the BBAA component of hexaploid common wheat possesses a significantly stronger capacity to buffer and sustain imbalanced D genome chromosomes and appears to harbor more structural chromosome variations than the BBAA genome of tetraploid wheat. We also document that this stronger capacity of the hexaploid BBAA subgenomes behaves as a genetically controlled dominant trait. Our findings bear implications to the known greater than expected level of genetic diversity in, and the remarkable adaptability of, hexaploid common wheat as a staple crop of global significance, as well as in using pentaploidy as intermediates for reciprocal introgression of useful traits between tetraploid and hexaploid wheat cultivars.

The poor lonesome A subgenome of Brassica napus var. Darmor (AACC) may not survive without its mate

Constitutive genomes of allopolyploid species evolve throughout their life span. However, the consequences of long-term alterations on the interdependency between each original genome have not been established. Here, we attempted an approach corresponding to subgenome extraction from a previously sequenced natural allotetraploid, offering a unique opportunity to evaluate plant viability and structural evolution of one of its diploid components. We employed two different strategies to extract the diploid AA component of the Brassica napus variety 'Darmor' (AACC, 2n = 4x = 38) and we assessed the genomic structure of the latest AA plants obtained (after four to five rounds of selection), using a 60K single nucleotide polymorphism Illumina array. Only one strategy was successful and the diploid AA plants that were structurally characterized presented a lower proportion of the B. napus A subgenome extracted than expected. In addition, our analyses revealed that some genes lost in a polyploid context appeared to be compensated for plant survival, either by conservation of genomic regions from B. rapa, used in the initial cross, or by some introgressions from the B. napus C subgenome. We conclude that as little as c. 7500 yr of coevolution could lead to subgenome interdependency in the allotetraploid B. napus as a result of structural modifications.

Transcriptome asymmetry in synthetic and natural allotetraploid wheats, revealed by RNA-sequencing

Allopolyploidization has occurred frequently within the Triticum-Aegilops complex which provides a suitable system to investigate how allopolyploidization shapes the expression patterns of duplicated homeologs. We have conducted transcriptome-profiling of leaves and young inflorescences in wild and domesticated tetraploid wheats, Triticum turgidum ssp. dicoccoides (BBAA) and ssp. durum (BBAA), an extracted tetraploid (BBAA), and a synthetic tetraploid (S(l) S(l) AA) wheat together with its diploid parents, Aegilops longissima (S(l) S(l) ) and Triticum urartu (AA). The two diploid species showed tissue-specific differences in genome-wide ortholog expression, which plays an important role in transcriptome shock-mediated homeolog expression rewiring and hence transcriptome asymmetry in the synthetic tetraploid. Further changes of homeolog expression apparently occurred in natural tetraploid wheats, which led to novel transcriptome asymmetry between the two subgenomes. In particular, our results showed that extremely biased homeolog expression can occur rapidly upon the allotetraploidzation and this trend is further enhanced in the course of domestication and evolution of polyploid wheats. Our results suggest that allopolyploidization is accompanied by distinct phases of homeolog expression changes, with parental legacy playing major roles in the immediate rewiring of homeolog expression upon allopolyploidization, while evolution and domestication under allotetraploidy drive further homeolog-expression changes toward re-established subgenome expression asymmetry.

Non-coding RNA-mediated epigenetic regulation of liver fibrosis

Hepatic stellate cells (HSC) activation plays a key role in liver fibrosis. Numerous studies have indicated that non-coding RNAs (ncRNAs) control liver fibrosis and fibroblasts proliferation. Greater knowledge of the role of the ncRNAs-mediated epigenetic mechanism in liver fibrosis could improve understanding of the liver fibrosis pathogenesis. The aim of this review is to describe the present knowledge about the ncRNAs significantly participating in liver fibrosis and HSC activation, and look ahead on new perspectives of ncRNAs-mediated epigenetic mechanism research. Moreover, we will discuss examples of non-coding RNAs that interact with histone modification or DNA methylation to regulate gene expression in liver fibrosis. Diverse classes of ncRNAs, ranging from microRNAs (miRs) to long non-coding RNAs (LncRNAs), have emerged as key regulators of several important aspects of function, including cell proliferation, activation, etc. In addition, recent advances suggest the important role of ncRNAs transcripts in epigenetic gene regulation. Targeting the miRs and LncRNAs can be a promising direction in liver fibrosis treatment. We discuss new perspectives of miRs and LncRNAs in liver fibrosis and HSC activation, mainly including interaction with histone modification or DNA methylation to regulate gene expression. These epigenetic mechanisms form powerful ncRNAs surveillance systems that may represent new targets for liver fibrosis therapeutic intervention.