The vascular targeted citrus FLOWERING LOCUS T3 gene promotes non-inductive early flowering in transgenic Carrizo rootstocks and grafted juvenile scions

Soares, Juliana M.; Weber, Kyle C.; Qiu, Wen-Ming; Stanton, Daniel; Mahmoud, Lamiaa M.; Wu, Hao; Huyck, Patrick; Zale, Janice; Jasim, Kawther Al; Grosser, Jude W.

doi:10.1038/s41598-020-78417-9

Cited by 24 publications

(25 citation statements)

References 93 publications

(115 reference statements)

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“…This hypothesis is also confirmed by Collani et al [66] who evidenced the role of the bZIP transcription factor FD (known to interact with FT at the shoot) in the regulation of GA metabolism. Recently, it was observed that transgenic Carrizo rootstock lines expressing the C. clementina FT gene under the control of the Arabidopsis thaliana phloem-specific SUCROSE SYNTHASE 2 (AtSUC2) promoter induce precocious flowering in non-transgenic "Valencia" scion [67]. The analysis of FT gene expression in non-transgenic scion leaves grafted onto FT transgenic rootstocks showed an increase of two-fold higher compared with shoots emerging from non-transgenic rootstocks at the fully open flower stage [67].…”

Section: Discussionmentioning

confidence: 99%

“…Recently, it was observed that transgenic Carrizo rootstock lines expressing the C. clementina FT gene under the control of the Arabidopsis thaliana phloem-specific SUCROSE SYNTHASE 2 (AtSUC2) promoter induce precocious flowering in non-transgenic "Valencia" scion [67]. The analysis of FT gene expression in non-transgenic scion leaves grafted onto FT transgenic rootstocks showed an increase of two-fold higher compared with shoots emerging from non-transgenic rootstocks at the fully open flower stage [67]. These results suggest an important role of rootstocks in the control of flowering by regulation of FT gene expression in the scion.…”

Section: Discussionmentioning

confidence: 99%

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Rootstock Affects Floral Induction in Citrus Engaging the Expression of the FLOWERING LOCUS T (CiFT)

et al. 2021

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In Citrus, flower induction represents the transition from vegetative to reproductive growth. The regulation of flower induction is mainly triggered by exposure to low temperatures and water-deficit stress, which activates the signaling cascade leading to an increased expression of the citrus orthologs of the FLOWERING LOCUS T (CiFT). In this study, the relationship between rootstock and flower induction under Mediterranean field conditions was investigated by monitoring the expression levels of the floral promoter CiFT2 in leaves of the pigmented sweet orange “Tarocco Scirè” grafted onto “C35” citrange and “Swingle” citrumelo rootstocks. The latter two are known to confer, respectively, high and low yield efficiency to the scion. In both rootstock/scion combinations, CiFT2 showed a seasonal expression with a peak during the inductive period in January triggered by cold temperature. The “Tarocco Scirè”/”C35” citrange combination showed the highest expression levels for CiFT2; this increased expression was correlated with yield and a higher number of flowers in the following spring, suggesting a significant effect of rootstocks on flower induction mediated by the overexpression of the CiFT2 gene.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Rootstock Affects Floral Induction in Citrus Engaging the Expression of the FLOWERING LOCUS T (CiFT)

et al. 2021

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“…One major challenge of employing strategies dependent on the grafting of transgenic materials containing editing transgenes is the graft transmissibility of FT protein, which has been shown in several instances when expressed via the commonly used 35S promoter not to be graft transmissible (Tränkner et al 2010;Zhang et al 2010;Zhang et al 2010;Wenzel et al 2013), with notable exceptions found in blueberry, Jatropha curcas, and citrus (Ye et al 2014;Song et al 2019;Soares et al 2020). Expression from phloem-companion cell-specific promoters (e.g., SUCROSE SYMPORTER 2 (SUC2)) rather than completely constitutive ones may increase the abundance of exportable FT protein to reach nearby grafted branches, as was recently shown in citrus (Soares et al 2020). Presumably, this improvement is because although 35S overexpression of FT is able to induce early flowering through direct expression at the shoot apex, it is insufficient in the phloem-companion cells to be able to reach the thresholds required for flowering when transmitted through graft junctions.…”

Section: Class IV Accelerated Flowering To Enable Transgene Removalmentioning

confidence: 99%

Gene editing in tree and clonal crops: progress and challenges

Goralogia

Redick²,

Strauss

2021

In Vitro Cell.Dev.Biol.-Plant

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Because of the limitations inherent in conventional breeding of trees and clonally propagated crops, gene editing is of great interest. Dozens of published papers attest to the high efficiency of CRISPR-based systems in clonal crops and trees. The opportunity for “clean” edits is expected to avoid or reduce regulatory burdens in many countries and may improve market acceptance. To date, however, nearly all studies in trees and clonal crops retained all of the gene editing machinery in the genome. Despite high gene editing efficiency, technical and regulatory obstacles are likely to greatly limit progress toward commercial use. Technical obstacles include difficult and slow transformation and regeneration, delayed onset of flowering or clonal systems that make sexual segregation of CRISPR-associated genes difficult, inefficient excision systems to enable removal of functional (protein- or RNA-encoding) transgenic DNA, and narrow host range or limited gene-payload viral systems for efficient transient editing. Regulatory obstacles include those such as in the EU where gene-edited plants are regulated like GMO crops, and the many forms of method-based systems that regulate stringently based on the method vs. product novelty and thus are largely applied to each insertion event. Other major obstacles include the provisions of the Cartagena Protocol with respect to international trade and the need for compliance with the National Environmental Policy Act in the USA. The USDA SECURE act has taken a major step toward a more science- and risk-based—vs. method and insertion event based—system, but much further regulatory and legal innovation is needed in the USA and beyond.

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“…Within 4–6 months of vector inoculation in different genotypes, flowering was initiated with no other phenotypic abnormalities. Furthermore, Soares et al (2020) reported a novel strategy to induce precocious flowering by overexpressing the Citrus clementina (CcFT3) orthologue under the control of AtSUC2 phloem-specific promoter in Carrizo citrange rootstocks. This strategy led to plants with normal morphology that flowered 16 months after transformation and, when juvenile scions were grafted, earlier flowering was also induced.…”

Section: Early Flowering Induction To Reduce the Juvenile Phase Of Transgenic Citrusmentioning

confidence: 99%

Citrus Genetic Transformation: An Overview of the Current Strategies and Insights on the New Emerging Technologies

et al. 2021

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Citrus are among the most prevailing fruit crops produced worldwide. The implementation of effective and reliable breeding programs is essential for coping with the increasing demands of satisfactory yield and quality of the fruit as well as to deal with the negative impact of fast-spreading diseases. Conventional methods are time-consuming and of difficult application because of inherent factors of citrus biology, such as their prolonged juvenile period and a complex reproductive stage, sometimes presenting infertility, self-incompatibility, parthenocarpy, or polyembryony. Moreover, certain desirable traits are absent from cultivated or wild citrus genotypes. All these features are challenging for the incorporation of the desirable traits. In this regard, genetic engineering technologies offer a series of alternative approaches that allow overcoming the difficulties of conventional breeding programs. This review gives a detailed overview of the currently used strategies for the development of genetically modified citrus. We describe different aspects regarding genotype varieties used, including elite cultivars or extensively used scions and rootstocks. Furthermore, we discuss technical aspects of citrus genetic transformation procedures via Agrobacterium, regular physical methods, and magnetofection. Finally, we describe the selection of explants considering young and mature tissues, protoplast isolation, etc. We also address current protocols and novel approaches for improving the in vitro regeneration process, which is an important bottleneck for citrus genetic transformation. This review also explores alternative emerging transformation strategies applied to citrus species such as transient and tissue localized transformation. New breeding technologies, including cisgenesis, intragenesis, and genome editing by clustered regularly interspaced short palindromic repeats (CRISPR), are also discussed. Other relevant aspects comprising new promoters and reporter genes, marker-free systems, and strategies for induction of early flowering, are also addressed. We provided a future perspective on the use of current and new technologies in citrus and its potential impact on regulatory processes.

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The vascular targeted citrus FLOWERING LOCUS T3 gene promotes non-inductive early flowering in transgenic Carrizo rootstocks and grafted juvenile scions

Cited by 24 publications

References 93 publications

Rootstock Affects Floral Induction in Citrus Engaging the Expression of the FLOWERING LOCUS T (CiFT)

Rootstock Affects Floral Induction in Citrus Engaging the Expression of the FLOWERING LOCUS T (CiFT)

Gene editing in tree and clonal crops: progress and challenges

Citrus Genetic Transformation: An Overview of the Current Strategies and Insights on the New Emerging Technologies

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