Populus serves as a model tree for biotechnology and molecular biology research due to the availability of the reference genome sequence of Populus trichocarpa (Torr. & Gray) genotype 'Nisqually-1'. However, 'Nisqually-1' has been shown to be very recalcitrant to micropropagation, regeneration and transformation. In this study, a highly efficient micropropagation protocol from greenhouse-grown shoot tips of 'Nisqually-1' was established. The optimal micropropagation protocol involves growing in vitro shoots in plant growth regulatorfree Murashige and Skoog (MS) basal medium supplemented with 3% sucrose, 0.3% Gelrite Ò and 5-10 g L -1 of activated charcoal. Plants grown on this medium were significantly longer, and contained significantly higher concentrations of chlorophyll. This highly effective protocol provides a consistent supply of quality leaf and stem materials throughout the year for transformation experiments and other in vitro manipulations, therefore eliminating inconsistency due to seasonal and greenhouse environmental variations and the need for repetitive tissue sterilization.

Auxin is a plant hormone that regulates many processes of plant growth such as apical dominance, cell growth, adventitious rooting, and fruit and seed development

COBRA proteins have been shown to be involved in both cell wall expansion and/or cellulose deposition. In this paper, we analyzed all 18 COBRA genes (PtCOBRA) from the completely sequenced Populus trichocarpa genome. The 14-member PtCOBRA subfamily I proteins have high similarities to the Arabidopsis (At) COB subfamily, and members with full length sequences were predicted to possess significant potentials for a GPI-anchor site. The 4-member PtCOBRA subfamily II proteins are 45% longer than subfamily I proteins and lack x-attachment sites at the C terminus, and are more similar to AtCOBL7 subfamily. The expression of the Populus COBRA family genes were regulated in a tissue-specific manner, and were shown to also respond differentially to inductions of hormones and environmental stimuli which affect plant cell expansion. The high levels of expressions, particularly in shoot tip and young root organs, suggests that at least some Populus COBRA genes are likely involved in regulating cell expansion.

Antibiotic-resistance genes of bacterial origin are invaluable markers for plant genetic engineering. However, these genes are feared to pose possible risk to human health by horizontal gene transfer from transgenic plants to bacteria, potentially resulting in antibiotic-resistant pathogenic bacteria; this is a considerable regulatory concern in some countries. The Atwbc19 gene, encoding an Arabidopsis thaliana ATP-binding cassette transporter, has been reported to confer resistance to kanamycin specifically as an alternative to bacterial antibiotic-resistance genes. In this report, we transformed hybrid aspen (Populus canescens x P. grandidentata) with the Atwbc19 gene. Unlike Atwbc19-transgenic tobacco that was only resistant to kanamycin, the transgenic Populus plants also showed resistance to three other aminoglycoside antibiotics (neomycin, geneticin, and paromomycin) at comparable levels to plants containing a CaMV35S-nptII cassette. Although it is unknown why the transgenic Populus with the Atwbc19 gene is resistant to all aminoglycoside antibiotics tested, the broad utility of the Atwbc19 gene as a reporter gene is confirmed here in a second dicot species. Because the Atwbc19 gene is plant-ubiquitous, it might serve as an alternative selectable marker to current bacterial antibiotic-resistance marker genes and alleviate the potential risk for horizontal transfer of bacterial-resistance genes in transgenic plants.

Reliable micropropagation protocols were developed for Japanese honeysuckle (Lonicera japonica Thunb.) and Amur honeysuckle [L. maackii (Rupr.) Maxim], two horticulturally important invasive woody plants. Shoot tips were collected from mature plants and established in vitro on Murashige and Skoog (MS) medium and cultured in various media. Plant growth regulators and basal media had significant effects on proliferation rates. Proliferation of Japanese honeysuckle was highest on Driver and Kuniyuki walnut (DKW) medium with 5 μM (1.1 ppm) 6-benzyladenine (BA), yielding an average of 14 axillary microshoots in 12 weeks, whereas Amur honeysuckle produced 38 axillary microshoots in 12 weeks on MS medium containing 2.5 μM (0.6 ppm) BA with or without 1.25 μM (0.3 ppm) indole-3-butyric acid (IBA). Microcuttings of Japanese honeysuckle were rooted ex vitro with or without treatment with 980 μM (200 ppm) IBA, whereas microcuttings of Amur honeysuckle required treatment with 980 μM (200 ppm) IBA to root. These protocols can be used to continuously produce plant materials for various biotechnological modifications, such as in vitro mutations and genetic engineering for noninvasiveness.