The dynamics of embolism refilling in abscisic acid (ABA)-deficient tomato plants.

Plants are in danger of embolism formation in xylem vessels when the balance between water transport capacity and transpirational demand is compromised. To maintain this delicate balance, plants must regulate the rate of transpiration and, if necessary, restore water transport in embolized vessels. Abscisic acid (ABA) is the dominant long-distance signal responsible for plant response to stress, and it is possible that it plays a role in the embolism/refilling cycle. To test this idea, a temporal analysis of embolism and refilling dynamics, transpiration rate and starch content was performed on ABA-deficient mutant tomato plants. ABA-deficient mutants were more vulnerable to embolism formation than wild-type plants, and application of exogenous ABA had no effect on vulnerability. However, mutant plants treated with exogenous ABA had lower stomatal conductance and reduced starch content in the xylem parenchyma cells. The lower starch content could have an indirect effect on the plant's refilling activity. The results confirm that plants with high starch content (moderately stressed mutant plants) were more likely to recover from loss of water transport capacity than plants with low starch content (mutant plants with application of exogenous ABA) or plants experiencing severe water stress. This study demonstrates that ABA most likely does not play any direct role in embolism refilling, but through the modulation of carbohydrate content, it could influence the plant's capacity for refilling

NPBTs FOR SUSTAINABLE VITICULTURE MANAGEMENT TO BIOTIC AND ABIOTIC STRESS

New plant breeding techniques (NPBTs) aim to overcome traditional breeding limits for plant improvement to biotic and abiotic stresses satisfying the European Policies requirements that promote chemical input reduction and a more sustainable agriculture. We decided to apply genome editing (via CRISPR/Cas9) focusing on susceptibility genes to control powdery mildew: we chosen to knock-out two genes belonging to MLO (Mildew Locus O) family: VvMLO7 and VvMLO6. The same approach was used to cope with abiotic stresses, in specifc drought, performing a knock-out of four genes, two belonging to GST (Glutathione S-Transferase) and two to PME (Pectin Methyl Esterase) gene families. In parallel to genome editing, we also applied cisgenesis to move the resistance locus RPV3-1 (Resistance to Plasmopara viticola) into economically important cultivars. This locus is formed by two di\ufb00erent genes that were inserted individually and in combination to evaluate their e\ufb00ects. One of the drawbacks linked to classical Agrobacterium tumefaciens mediated transformation is the insertion of unrelated transgene (e.g., antibiotic resistance). These markers are required for transgenic plants selection, but undesirable to be retained in commercial plants due to possible toxicity or allergenicity to humans and animals, in addition to their potential hazards for the environment. To overcome these limits, we exploit an inducible excision system based on a Cre-lox recombinase technology controlled by a heat-shock inducible promoter that will be activated once the transformation event(s) will be confrmed. Embryogenic calli of Chardonnay, Glera, Microvine, Pinot Noir, Sangiovese, were used in stable transformation with A. tumefaciens carrying the genome editing construct with the MLO-guideRNAs and the cisgenic construct carrying the two RPV3-1 genes. Embryogenic calli of rootstocks 110 Richter and SO4 were transformed with genome editing construct carrying GST and PME guideRNAs in two independent transformations. Regenerated embryos from all the transformation events are now under evaluation

New plant breeding technologies towards a more sustainable viticulture

European grapevine cultivars are highly susceptible to many pathogens that are managed through large pesticide use. Nevertheless, the European policies promote pesticide use reduction and new environmentally friendly methods for a more sustainable agriculture. In this framework, grapevine genetic improvement could benefit from New Plant Breeding Technologies. In order to reduce fungal susceptibility, we will produce knock-out plants from embryogenic calli using CRISPR/Cas9 technology. Studies in barley reported the acquisition of powdery mildew resistance by knocking out susceptibility genes belonging to the MLO (Mildew Locus O) family. In this study, our approach takes advantage from CRISPR/Cas9 technology to perform a multiple knockout of MLO genes. Among the 17 VvMLOs reported in grapevine we designed constructs to target VvMLO6 and VvMLO7. Golden Gate assembly was used to produce three different constructs (containing two guideRNAs for each gene) to knocking-out the targets singularly or by producing a double mutant. Usually, the genetic engineering techniques, mediated by A. tumefaciens, involve the insertion of exogenous selectable marker genes. These markers are required for selection of transgenic plants, but they are undesirable to be retained in commercial transgenic plants due to possible toxicity or allergenicity to humans and potential environmental hazard. To overcome these limits, we opted for a \u201cclean\u201d editing strategy developing an inducible excision system. This approach is based on a recombinase technology involving the Cre-loxP system from the P1 bacteriophage under a heat-shock inducible promoter to be activated once the editing event(s) will be confirmed. Obtainment of embryogenic calli is one of the main bottlenecks for application of CRISPR/Cas9: for two seasons, we collected inflorescences from Chardonnay, Glera, Microvine, Pinot Noir, Sangiovese cultivars and two rootstocks, 110 Richter and SO4, cultured and maintained in vitro up to embryo development and then used to perform Agrobacterium tumefaciens GV3101 mediated transformation

Editorial: Functional Genomics in Fruit Trees: From 'Omics to Sustainable Biotechnologies

This Research Topic of Frontiers in Plant Science collects 8 manuscripts, focused on fruit crops of high commercial interest, such as bayberry, blueberry, pear, grapevine, citrus, and walnut. The breadth of solutions and approaches that omics offer us today, and the applications and perspectives that are looming over a short time horizon, are illustrated with a particular focus on fruit qualitative traits, related to firmness and post-harvest (Cappai et al.), ripening (Honaas et al.), and lignin accumulation (Cao et al.), on improving knowledge on secondary metabolites, such as phenolic compounds (Saxe et al.), as well as on investigating earliest responses to pathogens (Wei et al.). Moreover, the Research Topic illustrates a technological application path from whole-genome sequencing (Wu et al.) to the resequencing (Tanaka et al.), to achieve the ultimate objective of modulating genes using the New Breeding Techniques (Salonia et al.)

Antiviral Activity of the G-Quadruplex Ligand TMPyP4 against Herpes Simplex Virus-1

The herpes simplex virus 1 (HSV-1) genome is extremely rich in guanine tracts that fold into G-quadruplexes (G4s), nucleic acid secondary structures implicated in key biological functions. Viral G4s were visualized in HSV-1 infected cells, with massive virus cycle-dependent G4-formation peaking during viral DNA replication. Small molecules that specifically interact with G4s have been shown to inhibit HSV-1 DNA replication. We here investigated the antiviral activity of TMPyP4, a porphyrin known to interact with G4s. The analogue TMPyP2, with lower G4 affinity, was used as control. We showed by biophysical analysis that TMPyP4 interacts with HSV-1 G4s, and inhibits polymerase progression in vitro; in infected cells, it displayed good antiviral activity which, however, was independent of inhibition of virus DNA replication or entry. At low TMPyP4 concentration, the virus released by the cells was almost null, while inside the cell virus amounts were at control levels. TEM analysis showed that virus particles were trapped inside cytoplasmatic vesicles, which could not be ascribed to autophagy, as proven by RT-qPCR, western blot, and immunofluorescence analysis. Our data indicate a unique mechanism of action of TMPyP4 against HSV-1, and suggest the unprecedented involvement of currently unknown G4s in viral or antiviral cellular defense pathways