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Abstract   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 regulator-free Murashige and Skoog (MS) basal medium supplemented with 3% sucrose, 0.3% Gelrite® 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. [ABSTRACT FROM AUTHOR]

Abstract  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. Expression of a family of YUCCA genes important for auxin biosynthesis has been shown to be spatially and temporally regulated in Arabidopsis. In this study, we report on the identification of 12 YUCCA genes from the completely sequenced Populus trichocarpa genome database and characterized them by comparing them with Arabidopsis YUCCA genes. The Populus YUCCA genes are distributed on eight chromosomes. All Populus and Arabidopsis YUCCA genes can be divided into two phylogenetic groups, one of which can be divided into two subgroups. Populus YUCCA genes are expressed in the shoot tip, immature and mature leaf, young root, stem, and bark tissues in an tissue-specific manner. Transcript accumulation of the Populus YUCCA genes is reduced by exogenous applications of various plant growth regulators except auxin. Steady-state mRNA levels of different Populus YUCCA genes vary considerably depending on the experimental treatments. These results suggest that, similar to the Arabidopsis and rice YUCCA genes, the Populus YUCCA genes may also have diversified roles in Populus growth and development, and their expression may be regulated in a complex manner by developmental and environmental cues. [ABSTRACT FROM AUTHOR]

Abstract  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 ω-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. [ABSTRACT FROM AUTHOR]