Selection of transgenic flax plants is facilitated by spectinomycin

A Simple but Effective Combination of pH Indicators for Plant Tissue Culture

The use of pH indicators provides a simple, semi-quantitative visual method for quickly assessing pH changes in tissue culture media; however, pH indicators are rarely used in routine plant tissue culture media. In this study, chlorophenol red, bromocresol purple, and bromocresol green were tested to assess their functionality in the growth medium for plant shoot cultures. In addition, a combination of bromocresol green and bromocresol purple was tested to determine if they would widen the observable colour change to better assess pH changes in the medium. Varying the ratio of bromocresol green to bromocresol purple alters the pH at which the colour changes from blue to green to yellow, with a 1:3 ratio providing a useful pH range of 5-6.5, while a 1:1 ratio provides a useful pH range of 4.5-6. All the pH indicators showed no toxic side effects for the plant species tested in this study and were able to be autoclaved to ensure media sterility. The addition of these pH indicators to quickly assess media pH in large tissue culture collections can aid in routine maintenance. These pH indicators can be used as a 'traffic light' system, with blue indicating a high pH, green a normal pH, and yellow a low pH in the media.

ER disruption and GFP degradation during non-regenerable transformation of flax with Agrobacterium tumefaciens

Flax is considered as plant species susceptible to Agrobacterium-mediated genetic transformation. In this study, stability of flax transformation by Agrobacterium rhizogenes versus Agrobacterium tumefaciens was tested by using combined selection for antibiotic resistance and visual selection of green fluorescent protein (GFP)-fusion reporter targeted to the endoplasmic reticulum (ER). Transformation with A. rhizogenes was stable for over 2 years, whereas transformation by A. tumefaciens resulted in non-regenerable stable transformation which was restricted solely to transgenic callus and lasted only 6-8 weeks. However, shoots regenerated from this callus appeared to be non-transgenic. Importantly, callus and root cells stably transformed with A. rhizogenes showed typical regular organization and dynamics of ER as visualized by GFP-ER marker. On the other hand, callus cells transformed with A. tumefaciens showed disintegrated ER structure and impaired dynamics which was accompanied with developmental degradation of GFP. Consequently, shoots which regenerated from such callus were all non-transgenic. Possible reasons for this non-regenerable flax transformation by A. tumefaciens are discussed.

Influence of light intensity and selection scheme on regeneration time of transgenic flax plants

This study aimed at establishing a protocol to increase the number of regenerated shoots and to limit the recovery of "escapes" during the regeneration of transgenic flax plants (cv Barbara). Here, we describe how light, adapted media and selection scheme could stimulate the transformation process, the organogenic potentiality of calli (by a factor of 3.2) and accelerate the transgenic shoot regeneration (by a factor of about 2). On comparison of the transformation rate observed while using low light (LL) and high light (HL) a considerable enhancement from 0.12 to 5.7% was evident. The promotive effect of light might also had a direct beneficial effect on transgenic plant production time leading to a reduction of more than 4 months in the time need to obtain transgenic seeds. All data indicate that HL plays a role on growth and on protein, rubisco and pigment contents by stimulating the gene implicated in photosynthetic and Calvin cycle processes.

Direct transformation of the liverwort Marchantia polymorpha L. by particle bombardment using immature thalli developing from spores

The liverwort, Marchantia polymorpha L., belongs to a group of basal land plants and is an emerging model for plant biology. We established a procedure to prepare sporangia of M. polymorpha under laboratory conditions by promoting its transition to reproductive development by far-red light irradiation. Here we report an improved direct transformation system of M. polymorpha using immature thalli developing from spores. Hygromycin-resistant transformants were obtained on selective media by transformation with a plasmid carrying the hygromycin-phosphotransferase gene (hpt) conferring hygromycin resistance in 4 weeks. The aminoglycoside-3''-adenyltransferase gene (aadA) conferring spectinomycin resistance was also successfully used as an additional selectable marker for nuclear transformation of M. polymorpha. The availability of the aadA gene in addition to the hpt gene should make M. polymorpha a versatile host for genetic manipulation. DNA gel-blot analyses indicated that transformed thalli carried a variable number of copies of the transgene integrated into the genome. Although the previous system using thalli grown from gemmae required a two-step selection in liquid and solid media for 8 weeks, the system reported here using thalli developing from spores allows generation of transformants in half the time by direct selection on solid media, facilitating genetic analyses in this model plant.

The use of the phosphomannose isomerase gene as alternative selectable marker for Agrobacterium-mediated transformation of flax (Linum usitatissimum)

In order to meet the future requirement of using non-antibiotic resistance genes for the production of transgenic plants, we have adapted the selectable marker system PMI/mannose to be used in Agrobacterium-mediated transformation of flax (Linum usitatissimum L.) cv. Barbara. The Escherichia coli pmi gene encodes a phosphomannose isomerase (E.C. 5.1.3.8) that converts mannose-6-phosphate, an inhibitor of glycolysis, into fructose-6-phosphate (glycolysis intermediate). Its expression in transformed cells allows them to grow on mannose-selective medium. The Agrobacterium tumefaciens strain GV3101 (pGV2260) harbouring the binary vector pNOV2819 that carries the pmi gene under the control of the Cestrum yellow leaf curling virus constitutive promoter was used for transformation experiments. Transgenic flax plants able to root on mannose-containing medium were obtained from hypocotyl-derived calli that had been selected on a combination of 20 g L(-1) sucrose and 10 g L(-1) mannose. Their transgenic state was confirmed by PCR and Southern blotting. Transgene expression was detected by RT-PCR in leaves, stems and roots of in vitro grown primary transformants. The mean transformation efficiency of 3.6%, that reached 6.4% in one experiment was comparable to that obtained when using the nptII selectable marker on the same cultivar. The ability of T1 seeds to germinate on mannose-containing medium confirmed the Mendelian inheritance of the pmi gene in the progeny of primary transformants. These results indicate that the PMI/mannose selection system can be successfully used for the recovery of flax transgenic plants under safe conditions for human health and the environment.