Adventitious shoot regeneration from in vitro cultured leaves of London plane tree (Platanus acerifolia Willd.)

Longer mtDNA Fragments Provide a Better Insight into the Genetic Diversity of the Sycamore Lace Bug, Corythucha ciliata (Say, 1832) (Tingidae, Hemiptera), Both in Its Native and Invaded Areas

Simple Summary

The sycamore lace bug (Corythucha ciliata Say, 1832) is one of the most abundant and widespread pests on plane trees (Platanus spp.) across the globe. The native range of the species is in North America, but it has been introduced to Europe (1964), South America (1985), Asia (1995), Australia (2006), and Africa (2014). To understand the genetic background behind this successful colonisation, we analysed a fragment (1356 bp) of the mitochondrial DNA. The 327 individuals revealed 17 haplotypes forming two separated groups. One group includes North American and Japanese individuals, while the other group comprises North American, European, and Asian individuals. We found a much higher genetic diversity in the native area (North America, 12 haplotypes) than in the invaded areas (Europe, five and Asia, four). The longer DNA fragment provided detailed information about the genetic structure of the species both in its native range and in the invaded areas, but the shorter DNA fragment could not provide a clear link between the genetic variation and the geographic origin.

Abstract

The sycamore lace bug (Corythucha ciliata Say, 1832) is of North American origin, but after its introduction to Europe (1964), South America (1985), Asia (1995), Australia (2006), and Africa (2014), it became an abundant and widespread pest on plane (Platanus spp.) trees. We analysed a 1356 bp long fragment of the mtDNA (COI gene) of 327 sycamore lace bug individuals from 38 geographic locations from Europe, Asia, and North America. Seventeen haplotypes (17 HTs) were detected. C. ciliata populations from North America exhibited higher haplotype diversity (12 HTs) than populations from Europe (6 HTs), Asia (4 HTs), or Japan (2 HTs). The haplotypes formed two haplogroups separated by at least seven mutation steps. One of these mutation steps includes HTs from North America and Japan. Another includes HTs from North America, Europe, and Asia. Haplotypes from Asia Minor, the Caucasus, and Central Asia are linked to haplotypes from Europe, while haplotypes found in Japan are linked to haplotypes found in North America only. The incorporation of published data from the GenBank into our dataset (altogether 517 individuals from 57 locations, but only 546 bp long fragment of the mtDNA) did not show any structure according to the geographic origin of the individuals.

Identification and characterization of PaGL1-like genes from Platanus acerifolia related to the regulation of trichomes

Two PaGL1-like genes were identified in London plane and functional in Arabidopsis, moreover, may play an important role in the regulation of trichome development in London plane. Trichome development is governed by a complex regulatory network. In Arabidopsis, subgroup 15 of the R2R3 MYB transcription factor family, which includes GLABRA1 (GL1), is involved in trichome development. In this study, we isolated and characterized two PaGL1-like genes from London plane (Platanus acerifolia). Sequence alignment and phylogenetic analysis indicated that these PaGL1-like genes are homologous to AtGL1. Quantitative real-time PCR (qRT-PCR) analysis showed that PaGL1-like1 was expressed in all of the tested organs taken from adult London plane trees, including trichomes, petioles after trichome removal, stems after trichome removal, and leaves after trichome removal, and also in the roots, cotyledons, hypocotyls and true leaves of seedlings. By contrast, the PaGL1-like2 was expressed only in the trichomes and leaves after trichome removal from adult trees, and in the cotyledons and true leaves of seedlings. Overexpression of PaGL1-like genes caused trichome abortion when transferred into wild type Arabidopsis and promoted trichome formation in the gl1 mutant. The expression profiles of some trichome-related genes were changed in transgenic Arabidopsis lines, and yeast two-hybrid analysis indicated that PaGL1-like proteins can directly interact with trichome-related bHLH proteins from both P. acerifolia and Arabidopsis. These results suggest that PaGL1-like genes are functional in Arabidopsis and may play an important role in the regulation of trichome development in London plane.

Data set useful for the micropropagation and the assessment of post-vitro genetic fidelity of veteran trees of P. orientalis L

The data presented in this article are related to the research article titled “Conservation of veteran trees within historical gardens (COVE): a case study applied to Platanus orientalis L. in central Italy” (Ciaffi et al., 2018) [1]. This article reports data on the composition of the substrates used in the different steps of Platanus orientalis micropropagation: establishment of in vitro culture, multiplication, elongation and rooting. Moreover, molecular data were used to assess the genetic fidelity of the micropropagated plants respect mother plants after three year of in vitro cultivation. Fifteen ISSR markers, used in “Determination of genetic stability of long-term micropropagated plantlets of Platanus acerifolia using ISSR markers” (Huang et al., 2009) [2] on P. acerifolia and in “Variant identification in Platanus occidentalis L. using SNP and ISSR markers” (Lee et al., 2012) [3] on P. occidentalis, were successfully employed in the present study on P. orientalis. The plant material was collected from the Renaissance garden of Villa Lante in Viterbo, Italy. It is envisioned that these data set will provide useful information for the conservation of veteran oriental plane trees of historical gardens.

Phylogeographic pattern of the plane leaf miner, Phyllonorycter platani (STAUDINGER, 1870) (Lepidoptera: Gracillariidae) in Europe

Background

The plane leaf miner, Phyllonorycter platani is a widely distributed insect species on plane trees and has a well-documented colonisation history in Europe over the last century. However, phylogeographic data of the species are lacking.

Results

We analysed 284 individuals from 38 populations across Europe, Asia, and North America. A 1242 bp fragment of the mitochondrial COI gene and an 893 bp fragment of the 28S rDNA has been Sanger sequenced. Twenty-four haplotypes were detected on the COI gene, and two alleles were identified on the 28S rDNA. We revealed two distinct clades for both markers reflecting the geographic origins, Asia and Europe. The genetic distance between the two main clades is 2.08% on the COI gene and 0.10% on the nuclear DNA.

An overlapping zone of the two clades was found across Eastern Europe and the Anatolian Peninsula. We detected heterozygote individuals of the 28S rDNA gene in Moldavia, Ukraine and in the southern part of Turkey. These suggest that the two clades can hybridise. Furthermore, the presence of European type homozygote individuals has been confirmed in the southern part of Turkey as well.

Conclusions

We have shown that both post-glacial recolonization and recent expansion events influenced the present genetic structure of P. platani. The genetic patterns revealed at least two refugia during the last ice age: one in the Balkan Peninsula and the other in the Caucasus region. Recent expansion was detected in some European and Central Asian populations. The two main clades (Europe/Asia) show definite genetic differences; however, several hybrid individuals were found in the overlapping zone as well (stretching over Eastern Europe and the Anatolian Peninsula). Discrepancies in mitochondrial and nuclear data indicate introgressions in the southern part of the Anatolian Peninsula.

Electronic supplementary material

The online version of this article (10.1186/s12862-018-1240-z) contains supplementary material, which is available to authorized users.

The FLOWERING LOCUS T orthologous gene of Platanus acerifolia is expressed as alternatively spliced forms with distinct spatial and temporal patterns

The FLOWERING LOCUS T (FT) protein is a likely component of the 'florigen' signal that plays a crucial role in regulating the transition from vegetative to reproductive growth. Here, we report the isolation of full-length cDNAs and the corresponding genomic clones encoding orthologous FT proteins (PaFT) of London plane (Platanus acerifolia Willd). Two genes with high sequence identity were isolated (PaFT1-2), but 34 different transcript products were identified, comprising 21 splice forms produced by alternative splicing of the PaFT pre-mRNAs. Expression of the alternative splicing forms of PaFT varied according to tissue type and developmental stage. PaFT transcripts were detected throughout adult trees, whereas in juvenile trees they were only detected in dormant sub-petiolar buds. In adult trees, levels of the various alternative splicing PaFT forms were related to flower development stage and tree dormancy. Ectopic expression of the archetypal splice form of PaFT-A in tobacco and Arabidopsis developed multiple altered phenotypes, notably early flowering and attenuation of apical dominance. The evidence in this study indicates that complex alternative processing of PaFT transcripts in P. acerifolia may be associated with multiple regulatory roles, including initiation of flowering, flower development, apical dominance, tree dormancy and dormancy release.

Extraction of high-quality tissue-specific RNA from London plane trees (Platanus acerifolia), permitting the construction of a female inflorescence cDNA library

The London plane tree (Platanus acerifolia Willd.) has global importance as an urban landscaping tree and is the subject of genetic-improvement programs for productive sterility, disease and/or insect resistance. Molecular analysis techniques are crucial to such programs, but may be impeded by specific difficulties encountered during nucleic acid isolation. A detailed RNA isolation and purification protocol, based on established cetyltrimethyl-ammonium bromide (CTAB) extraction techniques combined with additional purification steps using butanol and the ionic detergent CTAB, which overcomes these problems in the woody species P. acerifolia, was conducted. In short, phenolic compounds are bound to soluble polyvinylpyrrolidone and then separated out through LiCl precipitation of the RNA. Subsequently, protein- and carbohydrate-contaminants are removed by chloroform partitioning followed by LiCl-mediated precipitation. The resulting isolates of RNA were found to be of sufficient quality for successful use in reverse transcription PCR analysis. Furthermore, RNA isolates from female inflorescences were used for the construction of a cDNA library. This library was found to contain several full-length cDNA clones of MADS-box genes, consistent with the library being representative of inflorescence expression profiles.

Stable Agrobacterium-mediated genetic transformation of London plane tree (Platanus acerifolia Willd.)

London plane tree (Platanus acerifolia Willd.) is an important tree in urban landscaping but it suffers from a number of negative traits which genetic engineering could be used to address. As with many woody species, P. acerifolia has appeared recalcitrant to genetic transformation. However, the recent development of a method for regenerating shoots from P. acerifolia leaf explants suggests that such material could be a target for gene-transfer. Using an Agrobacterium tumefaciens strain in which the T-DNA carries the histochemically detected reporter gene beta-glucuronidase (GUS), we have followed the transfer of genes from Agrobacterium to leaf explants of Platanus acerifolia. Using this system, we have identified a set of inoculation and co-cultivation conditions (notably: the pre-treatment of leaf explants with 0.4 M mannitol, an inoculation period of 10 min, a bacterial OD(600) of 0.8-1.0 and a co-cultivation period of 5 days) that permit a good frequency and reliability of transient gene-transfer. Optimum levels of antibiotics for bacterial elimination and kanamycin-resistant shoot regeneration were also established. By applying these parameters, we recovered eight independent stably transformed shoots that were kanamycin-resistant and contained the nptII T-DNA gene, as confirmed by PCR analysis. Furthermore, Southern blot analysis confirmed that, in at least five of these lines, the transgene was associated with high molecular weight DNA, so indicating integration into the plant genome.

An efficient, in vitro cyclic production of shoots from adult trees of Crataeva nurvala Buch. Ham

An efficient, cyclic, two-step protocol for micropropagation of medicinal tree, Crataeva nurvala has been successfully developed, which can be employed at a commercial scale. Nodal explants from 30-year-old tree when cultured on MS medium supplemented with 2.22 microM BAP produced multiple shoots, which elongated satisfactorily on the same medium. Nodal and leaf explants from in vitro regenerated microshoots too developed shoots, thus making the process recurrent. In 6-month duration, owing to the recurring nature of the protocol, over 5400 shoots could be produced from a single nodal explant from the adult tree. Addition of casein hydrolysate significantly increased the average number of shoots per explant. Maximum number of shoots regenerated on medium supplemented with 100 mg l(-1) casein hydrolysate. Shoots could be rooted on 1/2 MS supplemented with 0.11 and 0.54 microM NAA. Regenerated plantlets were acclimatized and successfully transplanted to soil.