Plant transformation provides a key tool for much basic research, such as the study of gene functions and interactions, protein–protein interactions, developmental processes, as well as applications for crop improvement and the development of plant bioreactors to produce vaccines. Efficient and reproducible transformation technologies are not only essential for the development of transgenic plants but also critical for other applications like transient gene expression studies and gene editing.Instituto de BiotecnologíaFil: Hopp, Horacio Esteban. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Agrobiotecnología y Biología Molecular; ArgentinaFil: Hopp, Horacio Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Hopp, Horacio Esteban. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Fisiología, Biología Molecular y Celular; ArgentinaFil: Spangenberg, German. La Trobe University. Agriculture Victoria. AgriBio; AustraliaFil: Herrera-Estrella, Luis. Texas Tech University. Institute of Genomics for Crop Abiotic Stress Tolerance. Plant and Soil Science Department; Estados UnidosFil: Herrera-Estrella, Luis. Centro de Investigación y de Estudios Avanzados. Unidad de Genómica Avanzada. Laboratorio Nacional de Genómica para la Biodiversidad (LANGEBIO); Méxic

Herrera-Estrella, Luis

Hopp, Horacio Esteban

Spangenberg, German

Frontiers in Plant Science

English

PubMed

PubMed Central

Editorial: Plant Transformation

Repositorio Institucional – Biblioteca Digital

EDITORIALpublished: 18 April 2022doi: 10.3389/fpls.2022.876671Frontiers in Plant Science | www.frontiersin.org 1 April 2022 | Volume 13 | Article 876671Edited and reviewed by:Ruslan Kalendar,University of Helsinki, Finland*Correspondence:Horacio Esteban Hopphopp.esteban@inta.gob.arSpecialty section:This article was submitted toTechnical Advances in Plant Science,a section of the journalFrontiers in Plant ScienceReceived: 15 February 2022Accepted: 23 February 2022Published: 18 April 2022Citation:Hopp HE, Spangenberg G andHerrera-Estrella L (2022) Editorial:Plant Transformation.Front. Plant Sci. 13:876671.doi: 10.3389/fpls.2022.876671Editorial: Plant TransformationHoracio Esteban Hopp 1,2*, German Spangenberg 3 and Luis Herrera-Estrella 4,51Departamento de Fisiología, Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Universidad de BuenosAires (UBA), Buenos Aires, Argentina, 2 Instituto de Agrobiotecnología y Biología Molecular (IABIMO), UEDD INTA-CONICET,Hurlingham, Argentina, 3 AgriBio, Agriculture Victoria, La Trobe University, Melbourne, VIC, Australia, 4 Plant and Soil ScienceDepartment, Institute of Genomics for Crop Abiotic Stress Tolerance, Texas Tech University, Lubbock, TX, United States,5Unidad de Genómica Avanzada/LANGEBIO, Centro de Investigación y de Estudios Avanzados, Irapuato, MexicoKeywords: plant transformation, gene editing, selectable markers, transient expression, transformation protocolEditorial on the Research TopicPlant TransformationPlant transformation provides a key tool for much basic research, such as the study of genefunctions and interactions, protein–protein interactions, developmental processes, as well asapplications for crop improvement and the development of plant bioreactors to produce vaccines.Efficient and reproducible transformation technologies are not only essential for the developmentof transgenic plants but also critical for other applications like transient gene expression studiesand gene editing.Agrobacterium tumefaciens was first identified in 1907 as the etiological agent of crown galldisease. The bacterial factor responsible for tumor induction was described in the ‘70s: a DNAplasmid called the Ti plasmid by Zaenen et al. (1974). Transposon mutagenesis was used to dissectthe functional regions of the plasmid Ti, and two main regions were identified: (1) a segment ofthe Ti plasmid, denominated T-DNA, which is transferred into plant cells and integrated into theplant genome, and (2) a virulence region that provides all functions necessary for T-DNA transfer(for a review see Gelvin, 2000). The Ti plasmid was engineered by removing the genes responsiblefor tumor induction and replaced by dominant selectable markers to produce transgenic plants(Herrera-Estrella et al., 1983; Zambryski et al., 1983; De Block et al., 1984). Two repetitive 25 bpsequences at the right and left border were reported as essential for the transfer of the T-DNA(Wang et al., 1984). During the complex process of T-DNA integration into the plant genome,sometimes border T-DNA sequences are not recognized as limiting and vectors get integrated aswell, particularly in the case of the left border. To reduce the integration frequency of undesiredbackbone vector DNA segments Sahab and Taylor incorporated multiple left border repeats.Molecular analyses confirmed a 2-fold reduction of vector sequence integration when triple leftborders in three different transformation systems were tested including cassava transformation.Even though the first transgenic plants were produced in the early ‘80s, not all plant species aretransformed as easily as model species, particularly when it comes to some economically importantcrop species. Some plants are still considered as difficult or recalcitrant to transformation. Almostevery plant species has a specific transformation protocol that slowly evolved over the years andhas not been updated in the last two decades except for the methodology section of publishedpapers. Protocols were modified to facilitate new breeding techniques like gene editing, andsome of the latest methodological improvements include breakthrough advancements like theuse of developmental regulator genes and tissue-culture independent gene editing protocols.This Research Topic provides a collection of reviews and original research articles on the recentadvancement of plant transformation and gene editing of different crops. Below we briefly describethe original papers are reviews that integrate this Research Topic. Maize, perhaps the cropspecies with most transgenic commercial traits incorporated so far and for which many newHopp et al. Editorial: Plant Transformationapproaches to improve its engineering, including genomeediting, is critically summarized by Carvalho-Teixeira-Yassitepeet al.. In contrast, the genetic transformation of Teosinte themost closely related wild species of maize (phylogeneticallyspeaking) did not evolve as fast as its domesticated relative. Inthis context, Zobrist et al. report an innovative protocol by usingwhorl segments of seedlings germinated from mature seeds ofZea parviglumis.As mentioned above, efficient genetic transformation iscurrently performed routinely for many plant species, butthere are still many recalcitrant species. Even in species wheretransformation was successfully achieved, some agronomicallyimportant genotypes remain reluctant, thus slowing downbreeding programs since the obtention of new engineeredvarieties normally requires the introgression of transgenic orgene-edited traits into elite germplasm. Several reports in thisResearch Topic deal with this issue by improving tissue cultureconditions. For example, pluronic F-68 (PF-68) is a non-ionicsurfactant used in plant tissue culture as a growth additive.Kok et al. report that supplementation with specific PF-68concentrations enhances callus proliferation in recalcitrant ricecultivars. Chinese cabbage is another example of a recalcitrantcrop. Sivanandhan et al. report stableAgrobacterium tumefaciens-mediated transformation for Chinese cabbage cv. Kenshin byemploying antioxidants in the co-cultivation and subsequentregeneration media. TheAsteraceae family is the largest andmostdiversified family of the Angiosperms and includes economicallyimportant crops such as lettuce and sunflower. There is asharp contrast between lettuce that has easily adapted to tissueculture and transformation and sunflower, which is much trickierand difficult to transform. The peculiarities of their genetictransformation protocols are described by Darqui et al..Grapevine has been considered a recalcitrant crop to producetransgenic plants as several other woody perennials. The abilityto regenerate plants from transformed explants is consideredthe main obstacle in the process. State-of-the-art technologies toimprove grapevine transformation and regeneration are reviewedby Campos et al.. Switchgrass is a grass of importance forbiofuel production. Upland switchgrass cultivars are recalcitrantto genetic transformation. As for the case of the rice cultivarbelow, Xu et al. report improved transformation methods fortwo important upland cultivars. Speaking of forage crops andgrasses, dallisgrass is a very important apomictic pasture in SouthAmerica and other temperate warm regions of the world. In thepaper authored by Schrauf et al., the transformationmethodologystatus of cultivars of Paspalum dilatatum transformation isreviewed, and the authors propose this species as a model formolecular breeding in C4 perennial forage species. Althoughapomixis (asexual reproduction by seeds) is a pursued trait ingrasses because the introduced transgene becomes immediatelyfixed in a highly adapted genetic background capable of large-scale clonal propagation, it may present a serious constraint forconventional breeding. Another review (Bellido et al.) addressesthis paradox by describing the potential molecular pathwaysinvolved in apomixis determination and how these pathwayscould be used for both conventional and molecular breeding.Many crops belong to polyploid species and require the searchof systems to identify new dominant markers. A perspectivearticle from Jozefkowicz et al., proposes the use of the Tnt1element as a candidate to identify dominant mutations inallogamous tetraploid cultivated alfalfa. They illustrate thispotential by showing that a single allelic mutation in theMsNAC39 gene produces multifoliol leaf plants in alfalfa.Sugarcane is another complex polyploid (and aneuploid) species.Modern sugarcane cultivars have extremely large genomesoriginating from artificial interspecific crosses making traditionalbreeding extremely difficult. The review authored by Budegueret al. summarizes the current techniques and state of the artin sugarcane transformation. Potato is another well-studiedpolyploid crop of global importance that is not apomicticbut clonally propagated like apomictic grasses, sharing thedifficulties in conventional breeding. Thus, genetic engineeringprovides the opportunity to introduce/switch-off genes of interestwithout altering the allelic combination that characterizessuccessful commercial cultivars or to induce targeted sequencemodifications by genome editing. The review by Nahirñak et al.summarizes the latest developments in the field.Citruses are among the most prevailing fruit crops producedworldwide. As for the examples mentioned above, conventionalmethods are difficult because of prolonged juvenile periods,complex reproductive stages, occasional low fertility, self-incompatibility, parthenocarpy, or polyembryony. Geneticengineering technologies offer alternative approaches forovercoming these difficulties. The review by Conti et al. providesa detailed overview of the currently used strategies for thedevelopment of genetically modified citruses.Forest-tree breeding using transgenic technology is still inits early stages compared to annual plants except for a fewmodel species. In the review by Yin et al., the later advancesin transgenic technology of forest trees and their applicationfor trait improvement are discussed. Some forest species arewidely used in agroforestry plantations for soil stabilization,ecosystem rehabilitation, etc. This is the case of Casuarinaequisetifolia. In the study authored by Ren et al., more efficientand rapid regeneration systems based on stem segment explantsare reported.Another important aspect of molecular breeding is theidentification and characterization of complex industrial traits.This is the case of fiber length, strength, and other fiber qualityparameters in cotton. Razzaq et al. present an example of geneediting to improve fiber quality parameters appreciated by thetextile industry.Cannabis sativa produces unique phytocannabinoids andthere are scarce if any reports of in vivo engineering targetingthe cannabinoid biosynthesis genes. Matchett-Oates et al. reportthe successful modulation of cannabinoid biosynthesis genesusing RNAi via agroinfiltration, enabling functional genomics oftargeted cannabinoid biosynthesis genes.Finally, another woody plant was successfully transformedwith Bacillus thuringiensis toxin gene Cry10Aa to induce coffeeberry borer (CBB) resistance, as reported by Valencia-Lozanoet al.. Bioassays using transgenic fruits challenged withFrontiers in Plant Science | www.frontiersin.org 2 April 2022 | Volume 13 | Article 876671Hopp et al. Editorial: Plant TransformationCBB larvae and adults significantly reduced seed damage toless than 9%, providing a powerful CBB control tool forcoffee production.AUTHOR CONTRIBUTIONSHH was a guest associate editor of the Research Topicand wrote the paper text. GS and LH-E were guestassociate editors of the Research Topic and edited thetext. All authors contributed to the article and approvedthe submitted version.FUNDINGHH was supported by by the Agencia Nacionalde Promoción Científica y Tecnológica, Argentina(ANPCYT: PICT 2018-02926).ACKNOWLEDGMENTSWe thank authors of the papers published in this ResearchTopic for their valuable contributions and the referees for theirrigorous review.REFERENCESDe Block, M., Herrera-Estrella, L., Van Montagu, M., Schell, J., and Zambryski, P.(1984). Expression of foreign genes in regenerated plants and their progeny.EMBO J. 3, 1681–1689.Gelvin, S. B. (2000). Agrobacterium and plant genes involved in T-DNA transferand integration. Annu. Rev. Plant Physiol. Plant Mol. Biol. 51, 223–256.doi: 10.1146/annurev.arplant.51.1.223Herrera-Estrella, L., Depicker, A., Van Montagu, M., and Schell, J. (1983).Expression of chimaeric genes transferred into plant cells using a Ti-plasmid-derived vector. Nature 303, 209–213. doi: 10.1038/303209a0Wang, K., Herrera-Estrella, L., Van Montagu, M., and Zambryski, P. (1984).Right 25 by terminus sequence of the nopaline t-DNA is essentialfor and determines direction of DNA transfer from Agrobacteriumto the plant genome. Cell 38, 455–462. doi: 10.1016/0092-8674(84)90500-2Zaenen, I.,van Larebeke, N., Teuchy, H., Van Montagu, M., and Schell, J. (1974).Supercoiled circular DNA in crown-gall inducing Agrobacterium strains. J.Mol. Biol. 86, 109–127. doi: 10.1016/S0022-2836(74)80011-2Zambryski, P., Joos, H., Genetello, C., Leemans, J., Van Montagu, M., and Schell, J.(1983). Ti plasmid vector for the introduction of DNA into plant cells withoutalteration of their normal regeneration capacity. EMBO J. 2, 2143–2150.doi: 10.1002/j.1460-2075.1983.tb01715.xConflict of Interest: The authors declare that the research was conducted in theabsence of any commercial or financial relationships that could be construed as apotential conflict of interest.Publisher’s Note: All claims expressed in this article are solely those of the authorsand do not necessarily represent those of their affiliated organizations, or those ofthe publisher, the editors and the reviewers. Any product that may be evaluated inthis article, or claim that may be made by its manufacturer, is not guaranteed orendorsed by the publisher.Copyright © 2022 Hopp, Spangenberg and Herrera-Estrella. This is an open-accessarticle distributed under the terms of the Creative Commons Attribution License (CCBY). The use, distribution or reproduction in other forums is permitted, providedthe original author(s) and the copyright owner(s) are credited and that the originalpublication in this journal is cited, in accordance with accepted academic practice.No use, distribution or reproduction is permitted which does not comply with theseterms.Frontiers in Plant Science | www.frontiersin.org 3 April 2022 | Volume 13 | Article 876671

Editorial : Plant transformation

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Editorial : Plant transformation

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