Agrobacterium tumefaciens-mediated transformation of Phellodendron amurense Rupr. using mature-seed explants

Establishment and validation of a callus tissue transformation system for German chamomile (Matricaria chamomilla L.)

BACKGROUND

German chamomile (Matricaria chamomilla L.) is an important medicinal plant, and the essential oils in the flowers have various biological activities. Genetic transformation systems are important for plant quality improvement and molecular research. To the best of our knowledge, a genetic transformation system has not yet been reported for German chamomile.

RESULTS

In this study, we developed Agrobacterium-mediated transformation protocols for German chamomile callus tissues. This involved optimizing key parameters, such as hygromycin and cefotaxime concentrations, bacterial density, and infection and co-culture durations. We also performed gas chromatography-mass spectrometry analysis to identify volatile compounds in non-transgenic and transgenic callus and hairy root tissues. Furthermore, to compare and verify the callus transformation system of German chamomile, we transferred McFPS to the hairy roots of German chamomile. The results showed that the optimal conditions for Agrobacterium-mediated callus tissue transformation were as follows: explant, petiole; cefotaxime concentration, 300 mg/L; hygromycin concentration, 10 mg/L; and bacterial solution concentration, OD600 = 0.6; callus transformation efficiency was the highest when the co-culture time was 3 days.

CONCLUSIONS

Establishment of a high-efficiency callus transformation system will lay the foundation for gene function identification in German chamomile.

Overexpression of TaLEA3 induces rapid stomatal closure under drought stress in Phellodendron amurense Rupr

Late embryogenesis abundant (LEA) proteins participate in drought stress responses in plants. In the present study, the gene TaLEA3 from the drought-resistant plant Tamarix androssowii was transformed into Amur cork tree (Phellodendron amurense) via Agrobacterium tumefaciens to investigate the mechanism of stomatal closure in response to osmotic stress. Our results showed that P. amurense overexpressing TaLEA3 were resistant to drought stress by rapid stomatal closure. To study the stomatal movement regulated at the molecular level, a model system for stoma closure was established in in vitro P. amurense. In this work, we found that the increased Ca²⁺ accumulation in guard cells of transgenic plants caused stomatal closure and activated K⁺ efflux under polyethylene glycol (PEG) stress. Moreover, H⁺ changes might provide a needed pH condition for stomatal closure. Further, nitric oxide (NO) fluorescence was measured using an NO-specific fluorescent probe, diaminofluorescein-FM diacetate, which showed that guard cell NO fluorescence was stronger in transgenic plants compared with wild type plants. Additionally, five genes encoding nitrate reductase were up-regulated, indicating that TaLEA3 overexpression positively regulated NO biosynthesis and accumulation in the guard cells. This discovery will further our understanding of the LEA gene function and will help in engineering drought-resistant tree cultivars.

Agrobacterium-mediated genetic transformation and regeneration of transgenic plants using leaf midribs as explants in ramie [Boehmeria nivea (L.) Gaud]

In this study, leaf midribs, the elite explants, were used for the first time to develop an efficient regeneration and transformation protocol for ramie [Boehmeria nivea (L.) Gaud.] via Agrobacterium-mediated genetic transformation. Sensitivity of leaf midribs regeneration to kanamycin was evaluated, which showed that 40 mg l(-1) was the optimal concentration needed to create the necessary selection pressure. Factors affecting the ramie transformation efficiency were evaluated, including leaf age, Agrobacterium concentration, length of infection time for the Agrobacterium solution, acetosyringone concentration in the co-cultivation medium, and the co-cultivation period. The midrib explants from 40-day-old in vitro shoots, an Agrobacterium concentration at OD600 of 0.6, 10-min immersion in the bacteria solution, an acetosyringone concentration of 50 mg l(-1) in the co-cultivation medium and a 3-day co-cultivation period produced the highest efficiencies of regeneration and transformation. In this study, the average transformation rate was 23.25%. Polymerase chain reactions using GUS and NPTII gene-specific primers, Southern blot and histochemical GUS staining analyses further confirmed that the transgene was integrated into the ramie genome and expressed in the transgenic ramie. The establishment of this system of Agrobacterium-mediated genetic transformation and regeneration of transgenic plants will be used not only to introduce genes of interest into the ramie genome for the purpose of trait improvement, but also as a common means of testing gene function by enhancing or inhibiting the expression of target genes.

Agrobacterium tumefaciens-mediated genetic transformation of Salix matsudana Koidz. using mature seeds

An Agrobacterium tumefaciens-mediated transformation method was developed for Salix matsudana Koidz. using mature seeds as starting material. Multiple shoots were induced directly from embryonic shoot apices of germinating seeds. Although thidiazuron, 6-benzylaminopurine and zeatin induced multiple shoot induction with high frequency, zeatin (4.5 μM) was more effective for elongation of shoots and roots. The binary vector pCAMBIA1303, which contained neomycin phosphotransferase as a selectable marker gene and β-glucuronidase as a reporter gene, was used for transformation. Factors affecting transformation efficiency were examined for optimization of the procedure. Up to 35 of 180 seeds regenerated kanamycin-resistant shoots under optimal transformation conditions as follows: seeds were precultured for 4 days, apices of embryonic shoots were removed and infected with A. tumefaciens strain LBA4404 grown to a cell density equivalent (OD600) of 0.6, and then the infected explants were cultivated at 21 °C for 4 days. Storage of seeds at -20 °C for as long as 3 years had no significant effect on the induction of kanamycin-resistant shoots. Using this method, transgenic plants were obtained within ∼5 months with a transformation frequency of 7.2%. Analysis by polymerase chain reaction (PCR) showed that 36.4-93.8% of plants from all 13 tested kanamycin-resistant lines were PCR positive. Several 'escapes' were eliminated by a second round of selection. PCR, Southern blot and reverse transcriptase-PCR analyses of selected transgenic individuals 2 years after cutting propagation confirmed the successful generation of stable transformants. Our method, which minimizes the duration of axenic culture, may provide an alternative procedure for transformation of other recalcitrant Salix species.