SUMMARY
Camellia plants include more than 200 species of great diversity and immense economic, ornamental, and cultural values. We sequenced the transcriptomes of 116 Camellia plants from almost all ...sections of the genus Camellia. We constructed a pan‐transcriptome of Camellia plants with 89 394 gene families and then resolved the phylogeny of genus Camellia based on 405 high‐quality low‐copy core genes. Most of the inferred relationships are well supported by multiple nuclear gene trees and morphological traits. We provide strong evidence that Camellia plants shared a recent whole genome duplication event, followed by large expansions of transcription factor families associated with stress resistance and secondary metabolism. Secondary metabolites, particularly those associated with tea quality such as catechins and caffeine, were preferentially heavily accumulated in the Camellia plants from section Thea. We thoroughly examined the expression patterns of hundreds of genes associated with tea quality, and found that some of them exhibited significantly high expression and correlations with secondary metabolite accumulations in Thea species. We also released a web‐accessible database for efficient retrieval of Camellia transcriptomes. The reported transcriptome sequences and obtained novel findings will facilitate the efficient conservation and utilization of Camellia germplasm towards a breeding program for cultivated tea, camellia, and oil‐tea plants.
Significance Statement
High‐quality transcriptomes of 116 Camellia plants from almost all sections of genus Camellia unveils their deep phylogeny and the transcriptional mechanism underlying the dynamic evolution of quality traits related secondary metabolites, which will facilitate the efficient conservation and utilization of Camellia germplasm towards a breeding program for cultivated tea, camellia, and oil‐tea plants.
Bracts are the metamorphic non-flower organ in angiosperm plants. The variation of the color and shape of bracts was found to be neo-functionalized (i.e., similar to petals), garnering research ...interest as a pollinator attractor.
Bougainvillea
is known for its specialized, large, and colorful bracts, which contrast with its tiny colorless flowers. As a plant whose bracts vary greatly in terms of coloration, the molecular mechanisms for
Bougainvillea
bract coloration and polychroism are largely unknown. The lack of genomic information for
Bougainvillea
largely hinders studies into the evolution and genetic basis of bract color variation. In this study, a pan-transcriptome of bracts obtained from 18
Bougainvillea glabra
accessions was employed to investigate the global population-level germplasm kinship and the gene regulation network for bract color variation. Our results showed that the bracts of
B. glabra
accessions have largely differentiated International Commission on Illumination (CIE) L-a-b values. Moreover, germplasm kinship detected using principal component analysis, phylogeny, and admixture analysis showed three optimal subgroups, two of them distinctly clustered, which were not directly correlated with bract color variation at the population level. Differentially expressed genes (DEGs) between accessions of high vs. low L-a-b values revealed several considerable upregulated genes related to bract color L-a-b variation. A weighted gene co-expression network was constructed, and eight co-expressed regulation modules were identified that were highly correlated with variation in bract CIE L-a-b color values. Several candidate DEGs and co-expressed hub genes (e.g.,
GERD
,
SGR
,
ABCA3
,
GST
,
CYP76AD1
,
CYP76C
, and
JAZ
) that were tightly associated with bract color variation were eventually determined responsible for L-a-b colorations, which might be the core regulation factors contributing to the
B. glabra
bract color variation. This study provides valuable insights into the research on germplasm kinship, population-level pan-transcriptome expression profiles, and the molecular basis of color variation of key innovative bracts in horticultural
Bougainvillea
.
The Ascomycete fungus
is one of the primary causal agents of Esca, a widespread and damaging grapevine trunk disease. Variation in virulence among
isolates has been reported, but the underlying ...genetic basis of the phenotypic variability remains unknown. The goal of this study was to characterize intraspecific genetic diversity and explore its potential impact on virulence functions associated with secondary metabolism, cellular transport, and cell wall decomposition. We generated a chromosome-scale genome assembly, using single molecule real-time sequencing, and resequenced the genomes and transcriptomes of multiple isolates to identify sequence and structural polymorphisms. Numerous insertion and deletion events were found for a total of about 1 Mbp in each isolate. Structural variation in this extremely gene dense genome frequently caused presence/absence polymorphisms of multiple adjacent genes, mostly belonging to biosynthetic clusters associated with secondary metabolism. Because of the observed intraspecific diversity in gene content due to structural variation we concluded that a transcriptome reference developed from a single isolate is insufficient to represent the virulence factor repertoire of the species. We therefore compiled a pan-transcriptome reference of
comprising a non-redundant set of 15,245 protein-coding sequences. Using naturally infected field samples expressing Esca symptoms, we demonstrated that mapping of meta-transcriptomics data on a multi-species reference that included the
pan-transcriptome allows the profiling of an expanded set of virulence factors, including variable genes associated with secondary metabolism and cellular transport.
It has become clear in recent years that many genes in a given species may not be found in a single genotype thus using sequences from a single genotype as reference may not be adequate for various ...applications.
In this study we constructed a pan-transcriptome for barley by de novo assembling 288 sets of RNA-seq data from 32 cultivated barley genotypes and 31 wild barley genotypes. The pan-transcriptome consists of 756,632 transcripts with an average N50 length of 1240 bp. Of these, 289,697 (38.2%) were not found in the genome of the international reference genotype Morex. The novel transcripts are enriched with genes associated with responses to different stresses and stimuli. At the pan-transcriptome level, genotypes of wild barley have a higher proportion of disease resistance genes than cultivated ones.
We demonstrate that the use of the pan-transcriptome dramatically improved the efficiency in detecting variation in barley. Analysing the pan-transcriptome also found that, compared with those in other categories, disease resistance genes have gone through stronger selective pressures during domestication.
We have witnessed a rapid advancement in high-throughput genome sequencing and the maturation of long-read technologies. However, an accurate assembly of polyploid potato genomes still remains ...challenging. Sequencing the double-monoploid genome of Solanum tuberosum Group Phureja (Xu et al., Nature 475:189-195, 2011) has enabled functional studies of polyploid potato cultivars using RNA sequencing (RNA-Seq) technologies, although with the limitation of not covering cultivar-specific gene expression. The accumulated RNA-Seq datasets from these cultivars can be leveraged to assemble tetraploid potato transcriptomes that enable the analysis of genes that are not limited to reference genome annotations. To increase transcriptomes' quality, short-read assemblies are nowadays complemented with full-length transcriptome sequencing using Pacific Biosciences or Oxford Nanopore platforms. In this chapter we give a detailed guide on a pipeline for de novo transcriptome assembly of polyploid potato genotypes and their integration into a pan-transcriptome.
Tomato (Solanum lycopersicum) stress resistance and fruit total soluble solid (TSS) content have changed dramatically during selective breeding, and transcriptome variation has played a critical role ...in this rewiring. However, the single tomato reference genome impedes characterization of whole-transcriptome variation during domestication and breeding at the population level. Here, we constructed a pan-transcriptome of orange-stage tomato fruit, and investigated global expression presence/absence variation (ePAV) and differentially expressed genes (DEGs) based on RNA sequencing (RNA-seq) data from 399 tomato accessions. A total of 7 181 genes absent from the reference genome were identified, 6 122 of which were ePAV genes during tomato domestication and breeding including resistance genes such as late blight resistance gene PIM_DN29746_c0_g3_i1 and peroxidase P7-like gene PIM_DN30274_c0_g2_i1. In addition, 3 629 genes were significantly differentially expressed during tomato selection, among which 19 genes were associated with the reduced fruit TSS content of modern tomato cultivars, including LIN5, TIV1, and seven novel sugar transporter genes. Our results indicate that natural and artificial selection greatly shaped the tomato transcriptome, thereby altering the fruit TSS content and resistance to abiotic and biotic stresses.
Willows, in the genus Salix, are widespread on the earth with significant ecological and economic values for humans. Although about 500 Salix species have been estimated, the genomic foundation of ...their adaptations to environments with diverse stresses has been underexplored. Here, we applied a pan-transcriptome approach to investigate the phylogenetic relationships and genetic variations among 16 willow species. A pan-transcriptome of 29,668 gene families was assembled, 69% of which exhibited presence/absence variation across the analyzed species. In comparison to core genes present in all species, shell gene families absent in at least one species were enriched with genes in pathways of signaling transduction and response to stimuli, suggesting their functions in the interaction with diverse environmental factors. A phylogenetic tree of 16 willow species was constructed with high confidence based on 870 single-copy orthologous genes, providing detailed evolutionary relationships of willow sections. The willow species were further assigned into four species clusters using the gene numbers in each family. The diversity of gene family size and gene expression levels among the willow species are closely associated with their geographical distributions. The gene family members involved in DNA repair and cellular response to DNA damage stimuli were expanded in willow species from high-altitude regions in southwestern China, which may contribute to their tolerance to ultraviolet radiation stress. Our study generates a comprehensive pan-transcriptome resource for a large set of Salix species and provides insights into the adaptations of willows to diverse environments, which will be valuable for comparative analysis with other related woody and herbaceous plants.
Lentils (Lens sp.) are one of the main sources of protein for humans in many regions, in part because their rusticity allows them to withstand semi-dry climates and tolerate a wide spectrum of pests. ...Both are also highly sought-after attributes to face climate change. Wild accessions, rather than cultivated varieties, are typically the holders of most influential alleles for rusticity traits. However, most genomic and transcriptomic research conducted in lentils has been carried out on commercial accessions (L. culinaris), while wild relatives have been largely neglected. Herein, we assembled, annotated, and evaluated the transcriptomes of eight lentil accessions, including the cultivated Lens culinaris and the wild relatives: L. orientalis, L. tomentosus, L. ervoides, L. lamottei, L. nigricans, and two L. odemensis. The assemblies allowed, for the first time, a comparison among different lentil taxa at the coding sequence level, providing further insights into the evolutionary relationships between cultivated and wild germplasm and suggesting a grouping of the seven accessions into at least three conceivable gene pools. Moreover, orthologous clustering allowed a first estimation of the lentil pan-transcriptome. It is composed of 15,910 core genes, encoded in all accessions, and 24,226 accessory genes. The different pan-transcriptome clusters were also screened for Pfam-domain enrichment. The present study has a high novelty, as it is the first pan-transcriptome analysis using six wild species in addition to cultivated species. Because of the amount of transcript sequences provided, our findings will greatly boost lentil research and assist breeding efforts.
Mycotoxin contamination of maize kernels by fungal pathogens like Fusarium verticillioides and Aspergillus flavus is a chronic global challenge impacting food and feed security, health, and trade. ...Maize lipoxygenase genes (ZmLOXs) synthetize oxylipins that play defense roles and govern host-fungal interactions. The current study investigated the involvement of ZmLOXs in maize resistance against these two fungi. A considerable intraspecific genetic and transcript variability of the ZmLOX family was highlighted by in silico analysis comparing publicly available maize pan-genomes and pan-transcriptomes, respectively. Then, phenotyping and expression analysis of ZmLOX genes along with key genes involved in oxylipin biosynthesis were carried out in a maize mutant carrying a Mu transposon insertion in the ZmLOX4 gene (named UFMulox4) together with Tzi18, Mo17, and W22 inbred lines at 3- and 7-days post-inoculation with F. verticillioides and A. flavus. Tzi18 showed the highest resistance to the pathogens coupled with the lowest mycotoxin accumulation, while UFMulox4 was highly susceptible to both pathogens with the most elevated mycotoxin content. F. verticillioides inoculation determined a stronger induction of ZmLOXs and maize allene oxide synthase genes as compared to A. flavus. Additionally, oxylipin analysis revealed prevalent linoleic (18:2) peroxidation by 9-LOXs, the accumulation of 10-oxo-11-phytoenoic acid (10-OPEA), and triglyceride peroxidation only in F. verticillioides inoculated kernels of resistant genotypes.
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