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April 21, 2020

Closing the Yield Gap for Cannabis: A Meta-Analysis of Factors Determining Cannabis Yield.

Until recently, the commercial production of Cannabis sativa was restricted to varieties that yielded high-quality fiber while producing low levels of the psychoactive cannabinoid tetrahydrocannabinol (THC). In the last few years, a number of jurisdictions have legalized the production of medical and/or recreational cannabis with higher levels of THC, and other jurisdictions seem poised to follow suit. Consequently, demand for industrial-scale production of high yield cannabis with consistent cannabinoid profiles is expected to increase. In this paper we highlight that currently, projected annual production of cannabis is based largely on facility size, not yield per square meter. This meta-analysis of cannabis yields reported in scientific literature aimed to identify the main factors contributing to cannabis yield per plant, per square meter, and per W of lighting electricity. In line with previous research we found that variety, plant density, light intensity and fertilization influence cannabis yield and cannabinoid content; we also identified pot size, light type and duration of the flowering period as predictors of yield and THC accumulation. We provide insight into the critical role of light intensity, quality, and photoperiod in determining cannabis yields, with particular focus on the potential for light-emitting diodes (LEDs) to improve growth and reduce energy requirements. We propose that the vast amount of genomics data currently available for cannabis can be used to better understand the effect of genotype on yield. Finally, we describe diversification that is likely to emerge in cannabis growing systems and examine the potential role of plant-growth promoting rhizobacteria (PGPR) for growth promotion, regulation of cannabinoid biosynthesis, and biocontrol.

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April 21, 2020

Virulence characteristics and an action mode of antibiotic resistance in multidrug-resistant Pseudomonas aeruginosa.

Pseudomonas aeruginosa displays intrinsic resistance to many antibiotics and known to acquire actively genetic mutations for further resistance. In this study, we attempted to understand genomic and transcriptomic landscapes of P. aeruginosa clinical isolates that are highly resistant to multiple antibiotics. We also aimed to reveal a mode of antibiotic resistance by elucidating transcriptional response of genes conferring antibiotic resistance. To this end, we sequenced the whole genomes and profiled genome-wide RNA transcripts of three different multi-drug resistant (MDR) clinical isolates that are phylogenetically distant from one another. Multi-layered genome comparisons with genomes of antibiotic-susceptible P. aeruginosa strains and 70 other antibiotic-resistance strains revealed both well-characterized conserved gene mutations and distinct distribution of antibiotic-resistant genes (ARGs) among strains. Transcriptions of genes involved in quorum sensing and type VI secretion systems were invariably downregulated in the MDR strains. Virulence-associated phenotypes were further examined and results indicate that our MDR strains are clearly avirulent. Transcriptions of 64 genes, logically selected to be related with antibiotic resistance in MDR strains, were active under normal growth conditions and remained unchanged during antibiotic treatment. These results propose that antibiotic resistance is achieved by a “constitutive” response scheme, where ARGs are actively expressed even in the absence of antibiotic stress, rather than a “reactive” response. Bacterial responses explored at the transcriptomic level in conjunction with their genome repertoires provided novel insights into (i) the virulence-associated phenotypes and (ii) a mode of antibiotic resistance in MDR P. aeruginosa strains.

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April 21, 2020

A genomic resource derived from the integration of genome sequences, expressed transcripts and genetic markers in ramie.

The redundancy of genomic resources, including transcript and molecular markers, and their uncertain position in the genome have dramatically hindered the study of traits in ramie, an important natural fiber crop.We obtained a high-quality transcriptome consisting of 30,591 non-redundant transcripts using single-molecule long-read sequencing and proposed it as a universal ramie transcriptome. Additionally, 55,882 single nucleotide polymorphisms (SNPs) were identified and a high-density genetic map was developed. Based on this genetic map, 181.7?Mb ramie genome sequences were assembled into 14 chromosomes. For the convenient use of these resources, 29,286 (~?95.7%) of the transcripts and all 55,882 SNPs, along with 1827 previously reported sequence repeat markers (SSRs), were mapped into the ramie genome, and 22,343 (~?73.0%) transcripts, 50,154 (~?89.7%) SNPs, and 1466 (~?80.3%) SSRs were assigned to a specific location in the corresponding chromosome.This is the first study to characterize the ramie transcriptome by long-read sequencing, and the substantial number of transcripts of significant length obtained will accelerate our understanding of ramie growth and development. This integration of genome sequences, expressed transcripts, and genetic markers will provide an extremely useful resource for genetic, molecular, and breeding studies of ramie.

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April 21, 2020

The genome of broomcorn millet.

Broomcorn millet (Panicum miliaceum L.) is the most water-efficient cereal and one of the earliest domesticated plants. Here we report its high-quality, chromosome-scale genome assembly using a combination of short-read sequencing, single-molecule real-time sequencing, Hi-C, and a high-density genetic map. Phylogenetic analyses reveal two sets of homologous chromosomes that may have merged ~5.6 million years ago, both of which exhibit strong synteny with other grass species. Broomcorn millet contains 55,930 protein-coding genes and 339 microRNA genes. We find Paniceae-specific expansion in several subfamilies of the BTB (broad complex/tramtrack/bric-a-brac) subunit of ubiquitin E3 ligases, suggesting enhanced regulation of protein dynamics may have contributed to the evolution of broomcorn millet. In addition, we identify the coexistence of all three C4 subtypes of carbon fixation candidate genes. The genome sequence is a valuable resource for breeders and will provide the foundation for studying the exceptional stress tolerance as well as C4 biology.

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April 21, 2020

Long-Read Sequencing Emerging in Medical Genetics

The wide implementation of next-generation sequencing (NGS) technologies has revolutionized the field of medical genetics. However, the short read lengths of currently used sequencing approaches pose a limitation for identification of structural variants, sequencing repetitive regions, phasing alleles and distinguishing highly homologous genomic regions. These limitations may significantly contribute to the diagnostic gap in patients with genetic disorders who have undergone standard NGS, like whole exome or even genome sequencing. Now, the emerging long-read sequencing (LRS) technologies may offer improvements in the characterization of genetic variation and regions that are difficult to assess with the currently prevailing NGS approaches. LRS has so far mainly been used to investigate genetic disorders with previously known or strongly suspected disease loci. While these targeted approaches already show the potential of LRS, it remains to be seen whether LRS technologies can soon enable true whole genome sequencing routinely. Ultimately, this could allow the de novo assembly of individual whole genomes used as a generic test for genetic disorders. In this article, we summarize the current LRS-based research on human genetic disorders and discuss the potential of these technologies to facilitate the next major advancements in medical genetics.

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April 21, 2020

A new reference genome for Sorghum bicolor reveals high levels of sequence similarity between sweet and grain genotypes: implications for the genetics of sugar metabolism.

The process of crop domestication often consists of two stages: initial domestication, where the wild species is first cultivated by humans, followed by diversification, when the domesticated species are subsequently adapted to more environments and specialized uses. Selective pressure to increase sugar accumulation in certain varieties of the cereal crop Sorghum bicolor is an excellent example of the latter; this has resulted in pronounced phenotypic divergence between sweet and grain-type sorghums, but the genetic mechanisms underlying these differences remain poorly understood.Here we present a new reference genome based on an archetypal sweet sorghum line and compare it to the current grain sorghum reference, revealing a high rate of nonsynonymous and potential loss of function mutations, but few changes in gene content or overall genome structure. We also use comparative transcriptomics to highlight changes in gene expression correlated with high stalk sugar content and show that changes in the activity and possibly localization of transporters, along with the timing of sugar metabolism play a critical role in the sweet phenotype.The high level of genomic similarity between sweet and grain sorghum reflects their historical relatedness, rather than their current phenotypic differences, but we find key changes in signaling molecules and transcriptional regulators that represent new candidates for understanding and improving sugar metabolism in this important crop.

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April 21, 2020

Reviving the Transcriptome Studies: An Insight into the Emergence of Single-molecule Transcriptome Sequencing

Advances in transcriptomics have provided an exceptional opportunity to study functional implications of the genetic variability. Technologies such as RNA-Seq have emerged as state-of-the-art techniques for transcriptome analysis that take advantage of high-throughput next-generation sequencing. However, similar to their predecessors, these approaches continue to impose major challenges on full-length transcript structure identification, primarily due to inherent limitations of read length. With the development of single-molecule sequencing (SMS) from PacBio, a growing number of studies on the transcriptome of different organisms have been reported. SMS has emerged as advantageous for comprehensive genome annotation including identification of novel genes/isoforms, long non-coding RNAs and fusion transcripts. This approach can be used across a broad spectrum of species to better interpret the coding information of the genome, and facilitate the biological function study. We provide an overview of SMS platform and its diverse applications in various biological studies, and our perspective on the challenges associated with the transcriptome studies.

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April 21, 2020

Genomics-driven discovery of a biosynthetic gene cluster required for the synthesis of BII-Rafflesfungin from the fungus Phoma sp. F3723.

Phomafungin is a recently reported broad spectrum antifungal compound but its biosynthetic pathway is unknown. We combed publicly available Phoma genomes but failed to find any putative biosynthetic gene cluster that could account for its biosynthesis.Therefore, we sequenced the genome of one of our Phoma strains (F3723) previously identified as having antifungal activity in a high-throughput screen. We found a biosynthetic gene cluster that was predicted to synthesize a cyclic lipodepsipeptide that differs in the amino acid composition compared to Phomafungin. Antifungal activity guided isolation yielded a new compound, BII-Rafflesfungin, the structure of which was determined.We describe the NRPS-t1PKS cluster ‘BIIRfg’ compatible with the synthesis of the cyclic lipodepsipeptide BII-Rafflesfungin [HMHDA-L-Ala-L-Glu-L-Asn-L-Ser-L-Ser-D-Ser-D-allo-Thr-Gly]. We report new Stachelhaus codes for Ala, Glu, Asn, Ser, Thr, and Gly. We propose a mechanism for BII-Rafflesfungin biosynthesis, which involves the formation of the lipid part by BIIRfg_PKS followed by activation and transfer of the lipid chain by a predicted AMP-ligase on to the first PCP domain of the BIIRfg_NRPS gene.

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April 21, 2020

Reconstruction of the full-length transcriptome atlas using PacBio Iso-Seq provides insight into the alternative splicing in Gossypium australe.

Gossypium australe F. Mueller (2n?=?2x?=?26, G2 genome) possesses valuable characteristics. For example, the delayed gland morphogenesis trait causes cottonseed protein and oil to be edible while retaining resistance to biotic stress. However, the lack of gene sequences and their alternative splicing (AS) in G. australe remain unclear, hindering to explore species-specific biological morphogenesis.Here, we report the first sequencing of the full-length transcriptome of the Australian wild cotton species, G. australe, using Pacific Biosciences single-molecule long-read isoform sequencing (Iso-Seq) from the pooled cDNA of ten tissues to identify transcript loci and splice isoforms. We reconstructed the G. australe full-length transcriptome and identified 25,246 genes, 86 pre-miRNAs and 1468 lncRNAs. Most genes (12,832, 50.83%) exhibited two or more isoforms, suggesting a high degree of transcriptome complexity in G. australe. A total of 31,448 AS events in five major types were found among the 9944 gene loci. Among these five major types, intron retention was the most frequent, accounting for 68.85% of AS events. 29,718 polyadenylation sites were detected from 14,536 genes, 7900 of which have alternative polyadenylation sites (APA). In addition, based on our AS events annotations, RNA-Seq short reads from germinating seeds showed that differential expression of these events occurred during seed germination. Ten AS events that were randomly selected were further confirmed by RT-PCR amplification in leaf and germinating seeds.The reconstructed gene sequences and their AS in G. australe would provide information for exploring beneficial characteristics in G. australe.

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April 21, 2020

Divergent evolutionary trajectories following speciation in two ectoparasitic honey bee mites.

Multispecies host-parasite evolution is common, but how parasites evolve after speciating remains poorly understood. Shared evolutionary history and physiology may propel species along similar evolutionary trajectories whereas pursuing different strategies can reduce competition. We test these scenarios in the economically important association between honey bees and ectoparasitic mites by sequencing the genomes of the sister mite species Varroa destructor and Varroa jacobsoni. These genomes were closely related, with 99.7% sequence identity. Among the 9,628 orthologous genes, 4.8% showed signs of positive selection in at least one species. Divergent selective trajectories were discovered in conserved chemosensory gene families (IGR, SNMP), and Halloween genes (CYP) involved in moulting and reproduction. However, there was little overlap in these gene sets and associated GO terms, indicating different selective regimes operating on each of the parasites. Based on our findings, we suggest that species-specific strategies may be needed to combat evolving parasite communities. © The Author(s) 2019.

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April 21, 2020

Penaeid shrimp genome provides insights into benthic adaptation and frequent molting.

Crustacea, the subphylum of Arthropoda which dominates the aquatic environment, is of major importance in ecology and fisheries. Here we report the genome sequence of the Pacific white shrimp Litopenaeus vannamei, covering ~1.66?Gb (scaffold N50 605.56?Kb) with 25,596 protein-coding genes and a high proportion of simple sequence repeats (>23.93%). The expansion of genes related to vision and locomotion is probably central to its benthic adaptation. Frequent molting of the shrimp may be explained by an intensified ecdysone signal pathway through gene expansion and positive selection. As an important aquaculture organism, L. vannamei has been subjected to high selection pressure during the past 30 years of breeding, and this has had a considerable impact on its genome. Decoding the L. vannamei genome not only provides an insight into the genetic underpinnings of specific biological processes, but also provides valuable information for enhancing crustacean aquaculture.

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April 21, 2020

Mitochondrial genome and transcriptome analysis of five alloplasmic male-sterile lines in Brassica juncea.

Alloplasmic lines, in which the nuclear genome is combined with wild cytoplasm, are often characterized by cytoplasmic male sterility (CMS), regardless of whether it was derived from sexual or somatic hybridization with wild relatives. In this study, we sequenced and analyzed the mitochondrial genomes of five such alloplasmic lines in Brassica juncea.The assembled and annotated mitochondrial genomes of the five alloplasmic lines were found to have virtually identical gene contents. They preserved most of the ancestral mitochondrial segments, and the same candidate male sterility gene (orf108) was found harbored in mitotype-specific sequences. We also detected promiscuous sequences of chloroplast origin that were conserved among plants of the Brassicaceae, and found the RNA editing profiles to vary across the five mitochondrial genomes.On the basis of our characterization of the genetic nature of five alloplasmic mitochondrial genomes, we speculated that the putative candidate male sterility gene orf108 may not be responsible for the CMS observed in Brassica oxyrrhina and Diplotaxis catholica. Furthermore, we propose the potential coincidence of CMS in alloplasmic lines. Our findings lay the foundation for further elucidation of male sterility gene.

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April 21, 2020

Improved annotation of the domestic pig genome through integration of Iso-Seq and RNA-seq data.

Our understanding of the pig transcriptome is limited. RNA transcript diversity among nine tissues was assessed using poly(A) selected single-molecule long-read isoform sequencing (Iso-seq) and Illumina RNA sequencing (RNA-seq) from a single White cross-bred pig. Across tissues, a total of 67,746 unique transcripts were observed, including 60.5% predicted protein-coding, 36.2% long non-coding RNA and 3.3% nonsense-mediated decay transcripts. On average, 90% of the splice junctions were supported by RNA-seq within tissue. A large proportion (80%) represented novel transcripts, mostly produced by known protein-coding genes (70%), while 17% corresponded to novel genes. On average, four transcripts per known gene (tpg) were identified; an increase over current EBI (1.9 tpg) and NCBI (2.9 tpg) annotations and closer to the number reported in human genome (4.2 tpg). Our new pig genome annotation extended more than 6000 known gene borders (5′ end extension, 3′ end extension, or both) compared to EBI or NCBI annotations. We validated a large proportion of these extensions by independent pig poly(A) selected 3′-RNA-seq data, or human FANTOM5 Cap Analysis of Gene Expression data. Further, we detected 10,465 novel genes (81% non-coding) not reported in current pig genome annotations. More than 80% of these novel genes had transcripts detected in >?1 tissue. In addition, more than 80% of novel intergenic genes with at least one transcript detected in liver tissue had H3K4me3 or H3K36me3 peaks mapping to their promoter and gene body, respectively, in independent liver chromatin immunoprecipitation data. These validated results show significant improvement over current pig genome annotations.

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April 21, 2020

Analysis of genetic diversity of Xanthomonas oryzae pv. oryzae populations in Taiwan.

Rice bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo) is a major rice disease. In Taiwan, the tropical indica type of Oryza sativa originally grown in this area is mix-cultivated with the temperate japonica type of O. sativa, and this might have led to adaptive changes of both rice host and Xoo isolates. In order to better understand how Xoo adapts to this unique environment, we collected and analyzed fifty-one Xoo isolates in Taiwan. Three different genetic marker systems consistently identified five groups. Among these groups, two of them had unique sequences in the last acquired ten spacers in the clustered regularly interspaced short palindromic repeats (CRISPR) region, and the other two had sequences that were similar to the Japanese isolate MAFF311018 and the Philippines isolate PXO563, respectively. The genomes of two Taiwanese isolates with unique CRISPR sequence features, XF89b and XM9, were further completely sequenced. Comparison of the genome sequences suggested that XF89b is phylogenetically close to MAFF311018, and XM9 is close to PXO563. Here, documentation of the diversity of groups of Xoo in Taiwan provides evidence of the populations from different sources and hitherto missing information regarding distribution of Xoo populations in East Asia.

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April 21, 2020

Comprehensive characterization of T-DNA integration induced chromosomal rearrangement in a birch T-DNA mutant.

Integration of T-DNA into plant genomes via Agrobacterium may interrupt gene structure and generate numerous mutants. The T-DNA caused mutants are valuable materials for understanding T-DNA integration model in plant research. T-DNA integration in plants is complex and still largely unknown. In this work, we reported that multiple T-DNA fragments caused chromosomal translocation and deletion in a birch (Betula platyphylla × B. pendula) T-DNA mutant yl.We performed PacBio genome resequencing for yl and the result revealed that two ends of a T-DNA can be integrated into plant genome independently because the two ends can be linked to different chromosomes and cause chromosomal translocation. We also found that these T-DNA were connected into tandem fragment regardless of direction before integrating into plant genome. In addition, the integration of T-DNA in yl genome also caused several chromosomal fragments deletion. We then summarized three cases for T-DNA integration model in the yl genome. (1) A T-DNA fragment is linked to the two ends of a double-stranded break (DSB); (2) Only one end of a T-DNA fragment is linked to a DSB; (3) A T-DNA fragment is linked to the ends of different DSBs. All the observations in the yl genome supported the DSB repair model.In this study, we showed a comprehensive genome analysis of a T-DNA mutant and provide a new insight into T-DNA integration in plants. These findings would be helpful for the analysis of T-DNA mutants with special phenotypes.

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