Combining thermotherapy with shoot tip culture or cryotherapy for improved virus eradication from in vitro Actinidia macrosperma.

In recent years, kiwifruit viral diseases have become increasingly prevalent in kiwifruit producing regions of China, significantly impacting both the yield and quality of kiwifruit. This has emerged as a significant constraint on the healthy and sustainable development of the kiwifruit industry. The use of virus-free propagation materials has been proven to be an effective strategy for controlling plant viral diseases. In the present study, shoot tip culture (STC), shoot tip cryotherapy (Cryo), and their combinations with thermotherapy were established to eradicate AcVA, AcVB and AcCRaV from Actinidia macrosperma. Additionally, the impact of shoot tip size on virus eradication was evaluated. Among the three confirmed viruses, AcVB was the easiest to eradicate, followed by AcVA and AcCRaV. Combining thermotherapy with shoot tip culture or cryotherapy resulted in higher virus elimination rates than shoot tip culture or cryotherapy alone. Notably, the combination of thermotherapy and 0.5-1 mm shoot tip cryotherapy was shown to be the most effective protocol which produced 50% of regenerated shoots free from all the tested viruses. To the best of our knowledge, this is the first report on virus elimination from kiwifruit infected with multiple viruses based on conventional shoot tip culture and shoot tip cryotherapy.

Rapid and Visual Detection of Actinidia Chlorotic Ringspot-Associated Virus Using One-Step Reverse-Transcription Recombinase Polymerase Amplification Combined with Lateral Flow Dipstick Assay.

Actinidia chlorotic ringspot-associated virus (AcCRaV) occurs widely in major kiwifruit producing areas of China and is often accompanied by coinfecting viruses, affecting the growth, yield, and quality of kiwifruit. Therefore, a rapid and sensitive detection method is crucial for diagnosing and developing effective AcCRaV management strategies. In this study, a one-step reverse-transcription recombinase polymerase amplification combined with a lateral flow dipstick (RT-RPA-LFD) assay was developed for rapid detection of AcCRaV. Specific primers and a probe were designed based on the conserved region of the coat protein gene sequence of AcCRaV. The one-step RT-RPA reaction can be performed at 35 and 40°C within 10 to 30 min, and the amplification results can be read directly on the LFD within 5 min. The detection limit of the one-step RT-RPA-LFD assay was 10-8 ng (about 20 viral copies), which was equal with one-step RT-qPCR and 100 times more sensitive than one-step RT-PCR. Moreover, the one-step RT-RPA-LFD assay was successfully applied to detect AcCRaV from crude extracts, and the entire detection process can be completed within 40 min. These results indicate that the RT-RPA-LFD assay is a simple, rapid, and sensitive strategy that can be used for accurate diagnosis of AcCRaV-infected kiwifruit plants in the field. To our knowledge, this is the first study applying the one-step RT-RPA-LFD assay to detect a kiwifruit virus.

Micrografting: An Old Dog Plays New Tricks in Obligate Plant Pathogens.

Micrografting, which was developed almost 50 years ago, has long been used for virus eradication, micropropagation, regeneration, rejuvenation, and graft compatibility. Recently, micrografting has been used for studies of long-distance trafficking and signaling of molecules between scions and rootstocks. The graft transmissiveness of obligate plant pathogens, such as viruses, viroids, and phytoplasmas, facilitated the use of micrografting to study biological indexing and pathogen transmission, pathogen-induced graft incompatibility, and screening for the pathogen resistance during the past 20 years. The present study provides comprehensive information on the latter subjects. Finally, prospects are proposed to direct further studies.

Cryopreservation of shoot tips, evaluations of vegetative growth, and assessments of genetic and epigenetic changes in cryo-derived plants of Actinidia spp.

A droplet-vitrification protocol was described for cryopreservation of shoot tips of kiwifruit 'Yuxiang' (Actinidia chinensis var. deliciosa). No significant differences were found in root formation and shoot growth between the in vitro-derived shoots (the control) and cryo-derived ones when cultured in vitro. No significant differences were detected in survival and vegetative growth between the in vitro-derived plants (the control) and cryo-derived ones after re-establishment in greenhouse conditions. Inter-simple sequence repeat (ISSR) and amplified fragment length polymorphism (AFLP) did not detect any polymorphic bands in the cryo-derived shoots when cultured in vitro and the cryo-derived plants after re-establishment in greenhouse conditions. These data indicate rooting ability, vegetative growth and genetic stability are maintained in the cryo-derived kiwifruit plants recovered from the droplet-vitrification cryopreservation. Methylation sensitive amplification polymorphism (MSAP) detected 12.8% and 1.6% DNA methylation in the cryo-derived shoots when cultured in vitro and the cryo-derived plants after re-established in greenhouse conditions, respectively. This droplet-vitrification was applied to five cultivars and three rootstocks belonging to A. chinensis var. deliciosa, A. chinensis var. chinensis, A. macrosperma, A. polygama and A. valvata. The highest (68.3%) and lowest (22.5%) shoot regrowth were obtained in A. macrosperma and A. chinensis var. chinensis 'Jinmi', respectively, with an average of 46.4% shoot regrowth obtained across the eight genotypes. The droplet-vitrification protocol described here can be considered the most applicable cryopreservation method so far reported for the genus Actinidia. Results reported here provide theoretical and technical supports for setting up cryo-banks of genetic resources of Actinidia spp.

Characterization of Sox9-overexpressing human umbilical cord blood-derived mesenchymal stem cells-based engineered cartilage both in vitro and in vivo.

The source of seed cells is a critical factor for tissue engineering. The goal of this study was to evaluate the chondrogenesis of Sox9-overexpressing human umbilical cord mesenchymal stem cells (hUCMSCs) seeded onto bone matrix gelatin (BMG)/fibrin hybrid scaffolds both in vitro and in vivo. hUCMSCs were stably transfected with Sox9-expressing plasmid and grown on the three-dimensional BMG/fibrin hybrid scaffold for 8 weeks. Scanning electron microscopy and histochemistry were performed. The hUCMSC-loaded scaffolds were implanted into the subcutaneous layer of immunocompetent rats and chondrogenesis and host immune responses were monitored for 8 weeks. We found that hUCMSCs spread well and proliferated from 2 weeks after culturing. They produced abundant glycosaminoglycans and collagen II. At 8 weeks after implanting into rats, the hUCMSCs on the scaffolds formed cartilage-like tissue and displayed positive staining for toluidine blue, safranin O, Masson's trichrome, and collagen II. No significant changes in serum levels of lgG, lgA, lgM, C3, and C4 were observed after implantation of the hUCMSC-loaded scaffolds. Xenogeneic implantation of Sox9-overexpressing hUCMSCs embedded in the BMG/fibrin scaffolds promotes the formation of cartilage-like tissue without inducing evident host immune response. Therefore, Sox9-overexpressing hUCMSCs represent a promising cell candidate for cartilage tissue engineering. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1150-1155, 2017.