Parsley ubiquitin promoter displays higher activity than the CaMV 35S promoter and the chrysanthemum actin 2 promoter for productive, constitutive, and durable expression of a transgene in Chrysanthemum morifolium

Isolation and Functional Characterization of a Constitutive Promoter in Upland Cotton (Gossypium hirsutum L.)

Multiple cis-acting elements are present in promoter sequences that play critical regulatory roles in gene transcription and expression. In this study, we isolated the cotton FDH (Fiddlehead) gene promoter (pGhFDH) using a real-time reverse transcription-PCR (qRT-PCR) expression analysis and performed a cis-acting elements prediction analysis. The plant expression vector pGhFDH::GUS was constructed using the Gateway approach and was used for the genetic transformation of Arabidopsis and upland cotton plants to obtain transgenic lines. Histochemical staining and a β-glucuronidase (GUS) activity assay showed that the GUS protein was detected in the roots, stems, leaves, inflorescences, and pods of transgenic Arabidopsis thaliana lines. Notably, high GUS activity was observed in different tissues. In the transgenic lines, high GUS activity was detected in different tissues such as leaves, stalks, buds, petals, androecium, endosperm, and fibers, where the pGhFDH-driven GUS expression levels were 3-10-fold higher compared to those under the CaMV 35S promoter at 10-30 days post-anthesis (DPA) during fiber development. The results indicate that pGhFDH can be used as an endogenous constitutive promoter to drive the expression of target genes in various cotton tissues to facilitate functional genomic studies and accelerate cotton molecular breeding.

Development of virus-induced genome editing methods in Solanaceous crops

Genome editing (GE) using CRISPR/Cas systems has revolutionized plant mutagenesis. However, conventional transgene-mediated GE methods have limitations due to the time-consuming generation of stable transgenic lines expressing the Cas9/single guide RNA (sgRNA) module through tissue cultures. Virus-induced genome editing (VIGE) systems have been successfully employed in model plants, such as Arabidopsis thaliana and Nicotiana spp. In this study, we developed two VIGE methods for Solanaceous plants. First, we used the tobacco rattle virus (TRV) vector to deliver sgRNAs into a transgenic tomato (Solanum lycopersicum) line of cultivar Micro-Tom expressing Cas9. Second, we devised a transgene-free GE method based on a potato virus X (PVX) vector to deliver Cas9 and sgRNAs. We designed and cloned sgRNAs targeting Phytoene desaturase in the VIGE vectors and determined optimal conditions for VIGE. We evaluated VIGE efficiency through deep sequencing of the target gene after viral vector inoculation, detecting 40.3% and 36.5% mutation rates for TRV- and PVX-mediated GE, respectively. To improve editing efficiency, we applied a 37°C heat treatment, which increased the editing efficiency by 33% to 46% and 56% to 76% for TRV- and PVX-mediated VIGE, respectively. To obtain edited plants, we subjected inoculated cotyledons to tissue culture, yielding successful editing events. We also demonstrated that PVX-mediated GE can be applied to other Solanaceous crops, such as potato (Solanum tuberosum) and eggplant (Solanum melongena). These simple and highly efficient VIGE methods have great potential for generating genome-edited plants in Solanaceous crops.

Overcoming Difficulties in Molecular Biological Analysis through a Combination of Genetic Engineering, Genome Editing, and Genome Analysis in Hexaploid Chrysanthemum morifolium

Chrysanthemum is one of the most commercially important ornamental plants globally, of which many new varieties are produced annually. Among these new varieties, many are the result of crossbreeding, while some are the result of mutation breeding. Recent advances in gene and genome sequencing technology have raised expectations about the use of biotechnology and genome breeding to efficiently breed new varieties. However, some features of chrysanthemum complicate molecular biological analysis. For example, chrysanthemum is a hexaploid hyperploid plant with a large genome, while its genome is heterogeneous because of the difficulty of obtaining pure lines due to self-incompatibility. Despite these difficulties, an increased number of reports on transcriptome analysis in chrysanthemum have been published as a result of recent technological advances in gene sequencing, which should deepen our understanding of the properties of these plants. In this review, we discuss recent studies using gene engineering, genome editing, and genome analysis, including transcriptome analysis, to analyze chrysanthemum, as well as the current status of and future prospects for chrysanthemum.

Excision of DNA fragments with the piggyBac system in Chrysanthemum morifolium

Chrysanthemum morifolium is one of the most popular ornamental plants in the world. However, as C. morifolium is a segmental hexaploid, self-incompatible, and has a sizable heterologous genome, it is difficult to modify its trait systematically. Genome editing technology is one of the attractive methods for modifying traits systematically. For the commercial use of genetically modified C. morifolium, rigorous stabilization of its quality is essential. This trait stability can be achieved by avoiding further genome modification after suitable trait modification by genome editing. Since C. morifolium is a vegetatively propagated plant, an approach for removing genome editing tools is required. In this study, we attempted to use the piggyBac transposon system to remove specific DNA sequences from the C. morifolium genome. Using the luminescence as a visible marker, we demonstrated that inoculation of Agrobacterium harboring hyperactive piggyBac transposase removes inserted 2.6 kb DNA, which harbors piggyBac recognition sequences, from the modified Eluc sequence.

Strategies and Methods for Improving the Efficiency of CRISPR/Cas9 Gene Editing in Plant Molecular Breeding

Following recent developments and refinement, CRISPR-Cas9 gene-editing technology has become increasingly mature and is being widely used for crop improvement. The application of CRISPR/Cas9 enables the generation of transgene-free genome-edited plants in a short period and has the advantages of simplicity, high efficiency, high specificity, and low production costs, which greatly facilitate the study of gene functions. In plant molecular breeding, the gene-editing efficiency of the CRISPR-Cas9 system has proven to be a key step in influencing the effectiveness of molecular breeding, with improvements in gene-editing efficiency recently becoming a focus of reported scientific research. This review details strategies and methods for improving the efficiency of CRISPR/Cas9 gene editing in plant molecular breeding, including Cas9 variant enzyme engineering, the effect of multiple promoter driven Cas9, and gRNA efficient optimization and expression strategies. It also briefly introduces the optimization strategies of the CRISPR/Cas12a system and the application of BE and PE precision editing. These strategies are beneficial for the further development and optimization of gene editing systems in the field of plant molecular breeding.

Isolation and Functional Characterization of a Green-Tissue Promoter in Japonica Rice (Oryza sativa subsp. Japonica)

Simple Summary

Transgenic applications have largely focused on constitutive promoters in plants. However, strong and continuous over-expression of certain genes may be redundant and even harmful to plant growth. Thus, tissue-specific promoters are the most suitable for regulating target gene expression. Although several tissue-specific promoters have been identified, the regulatory mechanism of tissue-specific gene expression remains unclear. By a series of GUS staining of 5′ and 3′ deletions, we uncover tissue-specific cis-acting elements in GSX7R, including ten light-responsive elements. The results reveal that GSX7R is a reverse green tissue-specific promoter, except in endosperm. In contrast, strong tissue-specific promoters that can be used for rice improvements are limited. In this study, we successfully showed that the GSX7R promoter can drive the Cry1Ab gene to resistant rice yellow stem borer. In addition, our study demonstrates an effective promoter to drive foreign genes for crop improvement.

Abstract

Plant promoters play a vital role in the initiation and regulation of gene transcription. In this study, a rice protein/gene of unknown expression, named Os8GSX7, was gained from a rice T-DNA capture line. The semi-quantitative RT-PCR analysis showed that the gene was only expressed in root, glume, and flower, but not in stem, leaf, embryo, and endosperm of japonica rice. The GUS activity analysis of the GSX7R promoter showed that it was a reverse green tissue expression promoter, except in endosperm. The forward promoter of GSX7 cannot normally drive the expression of the foreign GUS gene, while the reverse promoter of GSX7 is a green tissue-specific expression promoter, which can drive the expression of the foreign GUS gene. The region from −2097 to −1543 bp was the key region for controlling the green tissue-specific expression. The regulatory sequences with different lengths from the 2097 bp reverse sequence from the upstream region of the Os8GSX7 were fused with the GUS reporter gene and stably expressed in rice. Furthermore, transgenic rice plants carrying Cry1Ab encoding Bacillus thuringiensis endotoxin, regulated by GSX7R, were resistant to yellow stem borer. The analysis suggested that 10 light responsive elements of tissue-specific expression were found, including ACE, Box4, CAT-box, G-Box, G-box, GATA motif, GC motif, I-box, Sp1, and chs-unit1 M1. In addition, the results of 5′ and 3′ deletions further speculated that ACE and I-box may be the key elements for determining the green tissue-specific expression of GSX7R promoter.

The truncated AaActin1 promoter is a candidate tool for metabolic engineering of artemisinin biosynthesis in Artemisia annua L

Malaria is a devastating parasitic disease with high levels of morbidity and mortality worldwide. Artemisinin, the active substance against malaria, is a sesquiterpenoid produced by Artemisia annua. To improve artemisinin content in the native A. annua plants, considerable efforts have been attempted, with genetic transformation serving as an effective strategy. Although, the most frequently-used cauliflower mosaic virus (CaMV) 35S (CaMV35S) promoter has proved to be efficient in A. annua transgenic studies, it appears to show weak activity in peltate glandular secretory trichomes (GSTs) of A. annua plants. Here, we characterized the 1727 bp fragment upstream from the translation start codon (ATG) of AaActin1, however, found it was inactive in tobacco. After removal of the 5' intron, the truncated AaActin1 promoter (tpACT) showed 69% and 50% activity of CaMV35S promoter in transiently transformed tobacco and stably transformed A. annua, respectively. β-glucuronidase (GUS) staining analysis showed that the tpACT promoter was capable of directing the constant expression of a foreign gene in peltate GSTs of transgenic A. annua, representing higher activity than CaMV35S promoter. Collectively, our study provided a novel promoter available for metabolic engineering of artemisinin biosynthesis in A. annua.

Optimizing sgRNA to Improve CRISPR/Cas9 Knockout Efficiency: Special Focus on Human and Animal Cell

During recent years, clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated protein 9 (Cas9) technologies have been noticed as a rapidly evolving tool to deliver a possibility for modifying target sequence expression and function. The CRISPR/Cas9 tool is currently being used to treat a myriad of human disorders, ranging from genetic diseases and infections to cancers. Preliminary reports have shown that CRISPR technology could result in valued consequences for the treatment of Duchenne muscular dystrophy (DMD), cystic fibrosis (CF), β-thalassemia, Huntington's diseases (HD), etc. Nonetheless, high rates of off-target effects may hinder its application in clinics. Thereby, recent studies have focused on the finding of the novel strategies to ameliorate these off-target effects and thereby lead to a high rate of fidelity and accuracy in human, animals, prokaryotes, and also plants. Meanwhile, there is clear evidence indicating that the design of the specific sgRNA with high efficiency is of paramount importance. Correspondingly, elucidation of the principal parameters that contributed to determining the sgRNA efficiencies is a prerequisite. Herein, we will deliver an overview regarding the therapeutic application of CRISPR technology to treat human disorders. More importantly, we will discuss the potent influential parameters (e.g., sgRNA structure and feature) implicated in affecting the sgRNA efficacy in CRISPR/Cas9 technology, with special concentration on human and animal studies.

Production of petaloid phenotype in the reproductive organs of compound flowerheads by the co-suppression of class-C genes in hexaploid Chrysanthemum morifolium

Functional suppression of two types of class-C genes caused transformation of pistils and stamens into petaloid organs that exhibit novel phenotypes, which gives a distinct gorgeous impression in the florets of chrysanthemum. The multiple-petal trait is a breeding objective for many horticultural plants. The loss of function of class-C genes causes the multiple-petal trait in several plant species. However, mechanisms involved in the generation of the multiple-petal trait are unknown in Chrysanthemum morifolium (chrysanthemum). Here, we isolated 14 class-C AGAMOUS (AG) genes, which were classified into two types of class-C genes, in chrysanthemum. Seven of these were categorized into CAG type 1 genes (CAG1s) and seven into CAG type 2 genes (CAG2s). Functions of class-C genes were co-suppressed by chimeric repressors and simultaneously knocked-down by RNAi to produce the multiple-petal phenotype in chrysanthemum. The expression of chimeric repressors of CAG1s and CAG2s caused morphological alteration of the pistils and stamens into petaloid organs in the ray and disk florets. Interestingly, the reproductive organs of the disk florets were transformed into petaloid organs similar to the petals of the disk florets, and those of the ray florets were transformed into petaloid organs such as the petals of the ray florets. Simultaneous knockdown of CAG1s and CAG2s expression by RNAi also exhibited a petaloid phenotype as observed in transgenic plants obtained by chimeric repressors. These results showed that CAG1s and CAG2s play important roles in the development of pistils and stamens, and the simultaneous repression of CAG1s and CAG2s resulted in a multiple-petal phenotype in chrysanthemum.

Turning Up the Temperature on CRISPR: Increased Temperature Can Improve the Editing Efficiency of Wheat Using CRISPR/Cas9

The application of CRISPR/Cas9 technologies has transformed our ability to target and edit designated regions of a genome. It's broad adaptability to any organism has led to countless advancements in our understanding of many biological processes. Many current tools are designed for simple plant systems such as diploid species, however, efficient deployment in crop species requires a greater efficiency of editing as these often contain polyploid genomes. Here, we examined the role of temperature to understand if CRISPR/Cas9 editing efficiency can be improved in wheat. The recent finding that plant growth under higher temperatures could increase mutation rates was tested with Cas9 expressed from two different promoters in wheat. Increasing the temperature of the tissue culture or of the seed germination and early growth phase increases the frequency of mutation in wheat when the Cas9 enzyme is driven by the ZmUbi promoter but not OsActin. In contrast, Cas9 expression driven by the OsActin promoter did not increase the mutations detected in either transformed lines or during the transformation process itself. These results demonstrate that CRISPR/Cas9 editing efficiency can be significantly increased in a polyploid cereal species with a simple change in growth conditions to facilitate increased mutations for the creation of homozygous or null knock-outs.