A simple and fast Agrobacterium-mediated transformation system for passion fruit KPF4 (Passiflora edulis f. edulis × Passiflora edulis f. flavicarpa)

Tissue culture and Agrobacterium-mediated genetic transformation of the oil crop sunflower

Sunflower is one of the four major oil crops in the world. 'Zaoaidatou' (ZADT), the main variety of oil sunflower in the northwest of China, has a short growth cycle, high yield, and high resistance to abiotic stress. However, the ability to tolerate adervesity is limited. Therefore, in this study, we used the retention line of backbone parent ZADT as material to establish its tissue culture and genetic transformation system for new variety cultivating to enhance resistance and yields by molecular breeding. The combination of 0.05 mg/L IAA and 2 mg/L KT in MS was more suitable for direct induction of adventitious buds with cotyledon nodes and the addition of 0.9 mg/L IBA to MS was for adventitious rooting. On this basis, an efficient Agrobacterium tumefaciens-mediated genetic transformation system for ZADT was developed by the screening of kanamycin and optimization of transformation conditions. The rate of positive seedlings reached 8.0%, as determined by polymerase chain reaction (PCR), under the condition of 45 mg/L kanamycin, bacterial density of OD600 0.8, infection time of 30 min, and co-cultivation of three days. These efficient regeneration and genetic transformation platforms are very useful for accelerating the molecular breeding process on sunflower.

Optimization of induction and hairy root culture establishment in two mullein species, Verbascum erianthum and Verbascum stachydiforme

The genus Verbascum, belonging to the family Scrophulariaceae, has a significant center of diversity in Iran. Two of its species, V. erianthum and V. stachydiforme, originate in the Iranian-Turanian region, but no studies have been conducted on the induction of their hairy roots. This genus is a valuable source of biologically active compounds such as iridoid glycosides and flavonoids. Hairy root culture is a suitable technique for the production and accumulation of secondary metabolites. Three different studies were conducted to optimize the induction and establishment of hairy roots. In the first experiment, the influence of explant type (leaf and hypocotyl), six infection methods, and co-culture time (48 and 72 h) on the efficiency of hairy root induction was investigated. The results showed that the highest hairy root induction (68.18%) was observed in the leaf explants inoculated by direct infection with three wounds within 72 h co-culture time. In the second experiment, the effect of four Agrobacterium rhizogenes strains (ATCC 15834, A4, A7, and A13) and leaf age (14, 21, and 28 days) on transformation efficiency and some morphological traits examined in both species were studied. The high transformation efficiency of hairy root (80.55%) was detected in the 21-day-old leaf explant of V. erianthum species that was inoculated with the A13 strain. The transformed hairy root colons were confirmed by PCR using rolB gene-specific primers. To optimize hairy root growth and avoid tissue browning, hairy roots were cultured in various media containing different antioxidants and improver agents (including ascorbic acid, citric acid, and NAA). The results showed that the highest fresh growth index (20.42) and the lowest tissue browning (9%) as well as total phenol (8.51 mg GA/g DW), and total flavonoid content (4.42 mg QUE/g DW) were obtained in medium B5 with 1.5 mg/l NAA.

Simplified Method for Agrobacterium-Mediated Genetic Transformation of Populus x berolinensis K. Koch

The rapid advancement of genetic technologies has made it possible to modify various plants through both genetic transformation and gene editing techniques. Poplar, with its rapid in vitro growth and regeneration enabling high rates of micropropagation, has emerged as a model system for the genetic transformation of woody plants. In this study, Populus × berolinensis K. Koch. (Berlin poplar) was chosen as the model organism due to its narrow leaves and spindle-shaped crown, which make it highly suitable for in vitro manipulations. Various protocols for the Agrobacterium-mediated transformation of poplar species have been developed to date. However, the genetic transformation procedures are often constrained by the complexity of the nutrient media used for plant regeneration and growth, which could potentially be simplified. Our study presents a cheaper, simplified, and relatively fast protocol for the Agrobacterium-mediated transformation of Berlin poplar. The protocol involved using internode sections without axillary buds as explants, which were co-cultivated in 10 µL droplets of bacterial suspension directly on the surface of a solid agar-based medium without rinsing and sterile paper drying after inoculation. We used only one regeneration Murashige and Skoogbased medium supplemented with BA (0.2 mg·L-1), TDZ (0.02 mg·L-1), and NAA (0.01 mg·L-1). Acetosyringone was not used as an induction agent for vir genes during the genetic transformation. Applying our protocol and using the binary plasmid pBI121 carrying the nptII selective and uidA reporter genes, we obtained the six transgenic lines of poplar. Transgenesis was confirmed through a PCR-based screening of kanamycin-selected regenerants for the presence of both mentioned genes, Sanger sequencing, and tests for detecting the maintained activity of both genes. The transformation efficiency, considering the 100 explants taken originally, was 6%.

Agrobacterium tumefaciens-Mediated Plant Transformation: A Review

Agrobacterium tumefaciens-mediated plant transformation is the most dominant technique for the transformation of plants. It is used to transform monocotyledonous and dicotyledonous plants. A. tumefaciens apply for stable and transient transformation, random and targeted integration of foreign genes, as well as genome editing of plants. The Advantages of this method include cheapness, uncomplicated operation, high reproducibility, a low copy number of integrated transgenes, and the possibility of transferring larger DNA fragments. Engineered endonucleases such as CRISPR/Cas9 systems, TALENs, and ZFNs can be delivered with this method. Nowadays, Agrobacterium-mediated transformation is used for the Knock in, Knock down, and Knock out of genes. The transformation effectiveness of this method is not always desirable. Researchers applied various strategies to improve the effectiveness of this method. Here, a general overview of the characteristics and mechanism of gene transfer with Agrobacterium is presented. Advantages, updated data on the factors involved in optimizing this method, and other useful materials that lead to maximum exploitation as well as overcoming obstacles of this method are discussed. Moreover, the application of this method in the generation of genetically edited plants is stated. This review can help researchers to establish a rapid and highly effective Agrobacterium-mediated transformation protocol for any plant species.

Advances in micropropagation, somatic embryogenesis, somatic hybridizations, genetic transformation and cryopreservation for Passiflora improvement

Passion fruit is an essential commercial plant in the tropics and subtropics, which has lately seen a rise in demand for high-quality fruits and large-scale production. Generally, different species of passion fruit (Passiflora sp.) are propagated by sexual reproduction. However, asexual reproduction, such as stem cuttings, grafting, or tissue culture, is also available and advantageous in many instances. Recent research on passion fruit has concentrated on improving and establishing methodologies for embryogenesis, clonal proliferation via (somatic embryos), homozygote regeneration (by anther culture), germplasm preservation (via cryopreservation), and genetic transformation. These developments have resulted in potentially new directions for asexual propagation. Even though effective embryo culture and cryogenics are now available, however the limited frequency of embryogenic callus transformation to ex-vitro seedlings still restricts the substantial clonal replication of passion fruit. Here, in this review the advancement related to biotechnological approaches and the current understanding of Passiflora tissue culture. In vitro culture, organogenesis, cryopreservation, breeding, and productivity of Passiflora will significantly improve with novel propagation approaches, which could be applied to a wider range of germplasm.

A simple and efficient protocol for transient transformation of sliced grape berries

Grape is an economically important crop but recalcitrant to Agrobacterium-mediated genetic transformation and in vitro regeneration. Here, we have developed a protocol for transient transformation of grapes by investigating the effects of explant pre-culture and duration of vacuum infiltration on transformation efficiency. Using sliced grape berries of "Shine-Muscat" (Vitis labrusca × Vitis vinifera) between the end of fruit expansion phase and the mature stage as explants, we firstly compared the effect of pre-culture explants into a susceptible state (incubation on Murashige and Skoog (MS) agar plate in the dark at 25 ± 1 °C for 48 h) with no pre-culture and then tested different vacuum infiltration times on transformation efficiency using β-glucuronidase (GUS) reporter system. Pre-culture increased the susceptibility of explants to the agrobacteria infection and increased transient transformation efficiency as assessed by histochemical GUS activity, with intense blue coloration compared with the faint staining observed in the non-susceptible explants. Using a Circulating Water Vacuum Pump system to facilitate agrobacteria entry into berry cells, we tested vacuum durations of 5, 10, and 15 min and observed that transformation efficiency increased with vacuum duration of infiltration. These results were confirmed by relative gene expression of GUS transgene as assessed by RT-qPCR and GUS activity assay. To further confirm the usefulness of our protocol, we transiently transformed grape berries with the hydrogen peroxide sensor gene VvHPCA3, and this was confirmed by gene expression analysis as well as increased sensitivity of the explants to hydrogen peroxide treatment. Overall, this study has resulted in a simple but efficient transient transformation protocol for grape berries and would be a valuable tool for the rapid testing of gene function and the study of key regulatory networks in this important crop.

Genome-wide identification of DnaJ gene family in Catalpa bungei and functional analysis of CbuDnaJ49 in leaf color formation

DnaJs are the common molecular chaperone proteins with strong structural and functional diversity. In recent years, only several DnaJ family members have been found to be able to regulate leaf color, and it remains to be explored whether there are other potential members that also regulate this character. Here, we identified 88 putative DnaJ proteins from Catalpa bungei, and classified them into four types according to their domain. Gene-structure analysis revealed that each member of CbuDnaJ family had same or similar exon-intron structure. Chromosome mapping and collinearity analysis showed that tandem and fragment duplication occurred in the process of evolution. Promoter analyses suggested that CbuDnaJs might be involved in a variety of biological processes. The expression levels of DnaJ family members in different color leaves of Maiyuanjinqiu were respectively extracted from the differential transcriptome. Among these, CbuDnaJ49 was the largest differentially expressed gene between the green and yellow sectors. Ectopic overexpression of CbuDnaJ49 in tobacco showed that the positive transgenic seedlings exhibited albino leaves, and the contents of chlorophyll and carotenoid were significantly reduced compared with those of wild type. The results suggested that CbuDnaJ49 played an important role in regulating leaf color. This study not only identified a novel gene of DnaJ family members regulating leaf color, but also provided new germplasm for landscaping.

Genome-wide identification and expression analysis of the SWEET gene family in daylily (Hemerocallis fulva) and functional analysis of HfSWEET17 in response to cold stress

BACKGROUND

The Sugars Will Eventually be Exported Transporters (SWEETs) are a newly discovered family of sugar transporters whose members exist in a variety of organisms and are highly conserved. SWEETs have been reported to be involved in the growth and development of many plants, but little is known about SWEETs in daylily (Hemerocallis fulva), an important perennial ornamental flower.

RESULTS

In this study, 19 daylily SWEETs were identified and named based on their homologous genes in Arabidopsis and rice. Phylogenetic analysis classified these HfSWEETs into four clades (Clades I to IV). The conserved motifs and gene structures showed that the HfSWEETs were very conservative during evolution. Chromosomal localization and synteny analysis found that HfSWEETs were unevenly distributed on 11 chromosomes, and there were five pairs of segmentally duplicated events and one pair of tandem duplication events. The expression patterns of the 19 HfSWEETs showed that the expression patterns of most HfSWEETs in different tissues were related to corresponding clades, and most HfSWEETs were up-regulated under low temperatures. Furthermore, HfSWEET17 was overexpressed in tobacco, and the cold resistance of transgenic plants was much higher than that of wild-type tobacco.

CONCLUSION

This study identified the SWEET gene family in daylily at the genome-wide level. Most of the 19 HfSWEETs were expressed differently in different tissues and under low temperatures. Overexpression further suggests that HfSWEET17 participates in daylily low-temperature response. The results of this study provide a basis for further functional analysis of the SWEET family in daylily.

Optimization of the Transformation Protocol for Increased Efficiency of Genetic Transformation in Hevea brasiliensis

The recurring growth of bacterium in newly developed resistant cells and a minimal level of bacterial infection rate are the main limiting factors of Agrobacterium-mediated transformation experiments in Hevea brasiliensis. The current study aimed to optimize crucial factors of the transformation protocol in order to obtain an efficient transformation experimental model for Hevea using cotyledonary somatic embryos as explants. Transformation conditions such as antibiotic concentration, preculture duration, Agrobacterium concentration, sonication and cocultivation conditions were analyzed using the binary vector pCAMBIA2301. Transient transformation was confirmed by GUS histochemical staining. The best transformation efficiency was observed when the explants were not cultured on a preculture medium that contained acetosyringone at a level of 100 μM. The best results were obtained using a bacterial density of 0.45 at OD 600 nm, 50 s of sonication of explants in a bacterial liquid culture and a total incubation time of 18 min in the same bacterial suspension. Transmission electron microscopical analysis confirmed the impacts of sonication on bacterial infection efficiency. Cocultivation conditions of 22 °C and 84 h of darkness were optimal for the transfer of T-DNA. Agrobacterium was eliminated with 500 mg/L of timentin, and the selection of transformants was performed using 100 mg/L of kanamycin in the selection medium. The presence of transgene was confirmed in the resistant embryos by polymerase chain reaction (PCR). The improved method of genetic transformation established in the present study will be useful for the introduction of foreign genes of interest into the Hevea genome for the breeding of this economically important plant species in the future.

Establishment of a Novel and Efficient Agrobacterium-Mediated in Planta Transformation System for Passion Fruit (Passiflora edulis)

Passion fruit (Passiflora edulis) is an important fruit crop with high economic value. Genetic engineering plays an important role in crop improvement with desired traits and gene functional studies. The lack of a simple, efficient, and stable transformation system for passion fruit has greatly limited gene functional studies. In this study, a simple and efficient Agrobacterium-mediated in planta transformation system for passion fruit was established, using Agrobacterium virulent strain EHA105 harboring the binary vectors pCAMBIA1301 and pCAMBIA1302 with GUS and GFP reporter genes. The system requires less time and labor costs than conventional transformation systems, and no additional phytohormones and sterile conditions are required. Regeneration efficiency of 86% and transformation efficiency of 29% were achieved, when the wounds were wrapped with Parafilm and the plants were kept in darkness for 15 days. Approximately 75% of the regenerated plants had a single shoot and 26% multiple shoots. The transformation was confirmed at the DNA and RNA levels as well as by GUS staining and GFP fluorescent measurements. The developed protocol will contribute to the genetic improvement of passion fruit breeding.

First report of passion fruit leaf blight caused by Nigrospora sphaerica in China

Passion fruit (Passiflora edulis Sims) is a widely cultivated dicotyledonous perennial plant with woody vines (Asande et al. 2020). In November 2020, leaf blight was observed on leaves of P. edulis (cultivar: 'Panama Red') newly planted in Wangyou, Huishui county, Guizhou province, China (25°82'57" N, 106°50'49" E). The leaf blight occurred on both young and old leaves, starting from the margins, and then extended to the entire leaves. The color of the affected tissue was brown with a yellow hallo in the early period, and then gradually turned to grey. The disease incidence was 60%-70% on a 0.08-ha field. Following isolation of the potential pathogen from 12 diseased leaves, nine isolates were obtained. The colonies were white with a regular round shape at the early stage and became black with fluffy hyphae after eight days on potato dextrose agar (PDA) medium, incubated at 25°C in the dark for 10 days. The single cell conidia were solitary, spherical or slightly ellipsoidal, black, shiny, smooth, aseptate, spherical, and 8.1-13.5 μm (n=50) in diameter. Conidiophores (5.2-9.9 × 4.4-7.2 μm) were mostly reduced to conidiogenous cells and aggregated in clusters on hyphae. Conidiogenous cells were hyaline to pale brown or black, globose to ampulliform or clavate. Morphological characteristics of the isolates matched the description of the genus Nigrospora Mei Wang & L. Cai (Wang et al. 2017). For molecular identification, DNA was extracted, and PCRs were performed with primers ITS1/ITS4 for the ITS region (White et al. 1990), primers Bt2a/Bt2b for the β-tubulin gene (TUB) (Glass and Donaldson 1995), and primers EF1-728F/EF1-986R for the translation elongation factor 1-alpha gene (EF1-α) (Carbone and Kohn 1999). Representative sequences of the ITS region, EF1-α, and TUB sequences (from isolate WYR007) were deposited in GenBank (accession numbers: MW561355; MZ053463; MZ032030) and are included in the supplementary materials. BLAST analysis against sequences from previously published studies showed 99.58% (ITS region), 99.54% (EF1-α), and 99.45% (TUB) identity to Nigrospora sphaerica sequences (accession numbers: MN215808.1; MN864137.1; KY019606.1). In addition, homology was confirmed with a phylogenetic tree using concatenated sequences from ITS, EF1-α and TUB constructed with MEGA 7 for which the maximum likelihood method was used with 1,000 bootstrapping iterations. To complete Koch's postulates, conidia suspensions of isolate WYR007 (prepared from 1-month-old colonies in 0.05% Tween 20 buffer and adjusted to a concentration of 1 × 103 conidia/mL) were sprayed on 15 leaves (200 μL per leaf) of 5 one-year-old healthy P. edulis plants (cultivar: 'Panama Red'). The same number of leaves from control group plants was only treated with 0.05% Tween buffer. All plants were incubated at 26°C ± 2°C under a 16 h/8 h photoperiod and 70%-75% relative humidity (RH) after inoculation. After 14 days, symptomatic blight appeared on all inoculated leaves. In contrast, no symptoms appeared on leaves in the control group. The disease assays were repeated three times. Pure cultures were re-isolated from diseased leaves and confirmed to be N. sphaerica based on the morphological and molecular methods mentioned above (ITS region, the TUB, and the EF1-α sequences). To our knowledge, this study is the first report of N. sphaerica as a pathogen on P. edulis causing leaf blight. The identification of the pathogen could provide relevant background for its future management.s Sims) is a widely cultivated dicotyledonous perennial plant with woody vines (Asande et al. 2020). In November 2020, leaf blight was observed on leaves of P. edulis (cultivar: 'Panama Red') newly planted in Wangyou, Huishui county, Guizhou province, China (25°82'57" N, 106°50'49" E). The leaf blight occurred on both young and old leaves, starting from the margins, and then extended to the entire leaves. The color of the affected tissue was brown with a yellow hallo in the early period, and then gradually turned to grey. The disease incidence was 60%-70% on a 0.08-ha field. Following isolation of the potential pathogen from 12 diseased leaves, nine isolates were obtained. The colonies were white with a regular round shape at the early stage and became black with fluffy hyphae after eight days on potato dextrose agar (PDA) medium, incubated at 25°C in the dark for 10 days. The single cell conidia were solitary, spherical or slightly ellipsoidal, black, shiny, smooth, aseptate, spherical, and 8.1-13.5 μm (n=50) in diameter. Conidiophores (5.2-9.9 × 4.4-7.2 μm) were mostly reduced to conidiogenous cells and aggregated in clusters on hyphae. Conidiogenous cells were hyaline to pale brown or black, globose to ampulliform or clavate. Morphological characteristics of the isolates matched the description of the genus Nigrospora Mei Wang & L. Cai (Wang et al. 2017). For molecular identification, DNA was extracted, and PCRs were performed with primers ITS1/ITS4 for the ITS region (White et al. 1990), primers Bt2a/Bt2b for the β-tubulin gene (TUB) (Glass and Donaldson 1995), and primers EF1-728F/EF1-986R for the translation elongation factor 1-alpha gene (EF1-α) (Carbone and Kohn 1999). Representative sequences of the ITS region, EF1-α, and TUB sequences (from isolate WYR007) were deposited in GenBank (accession numbers: MW561355; MZ053463; MZ032030) and are included in the supplementary materials. BLAST analysis against sequences from previously published studies showed 99.58% (ITS region), 99.54% (EF1-α), and 99.45% (TUB) identity to Nigrospora sphaerica sequences (accession numbers: MN215808.1; MN864137.1; KY019606.1). In addition, homology was confirmed with a phylogenetic tree using concatenated sequences from ITS, EF1-α and TUB constructed with MEGA 7 for which the maximum likelihood method was used with 1,000 bootstrapping iterations. To complete Koch's postulates, conidia suspensions of isolate WYR007 (prepared from 1-month-old colonies in 0.05% Tween 20 buffer and adjusted to a concentration of 1 × 103 conidia/mL) were sprayed on 15 leaves (200 μL per leaf) of 5 one-year-old healthy P. edulis plants (cultivar: 'Panama Red'). The same number of leaves from control group plants was only treated with 0.05% Tween buffer. All plants were incubated at 26°C ± 2°C under a 16 h/8 h photoperiod and 70%-75% relative humidity (RH) after inoculation. After 14 days, symptomatic blight appeared on all inoculated leaves. In contrast, no symptoms appeared on leaves in the control group. The disease assays were repeated three times. Pure cultures were re-isolated from diseased leaves and confirmed to be N. sphaerica based on the morphological and molecular methods mentioned above (ITS region, the TUB, and the EF1-α sequences). To our knowledge, this study is the first report of N. sphaerica as a pathogen on P. edulis causing leaf blight. The identification of the pathogen could provide relevant background for its future management.