The primary growth occurs at the top of the stem a few internodes below the SAM. The vasculature develops from the procambium of the primary stem. In the stem, primary growth originates in the shoot apical meristem (SAM) and is responsible for production of leaves and stems. Many plants, especially trees, show two distinct types of growth patterns, known as primary and secondary growth (reviewed in Baucher et al., 2007). In the plant, wood serves many functions in water/nutrient transport, mechanical support, and storage of organic compounds, water, and gases ( Brunner et al., 2004). From ecological and evolutionary perspectives, wood plays an important role in the global carbon biogeochemical cycle as it dominates terrestrial ecosystem biomass ( Kirilenko and Sedjo, 2007 Bonan, 2008). Wood provides a renewable resource for the production of pulp, paper, and construction timber ( Skog and Nicholson, 1998) and is growing in importance as a lignocellulosic feedstock for biofuel production ( Ragauskas et al., 2006). A set of four LBD genes, including the LBD1 gene, was predominantly expressed in wood-forming tissues, suggesting a broader regulatory role of these transcription factors during secondary woody growth in poplar. Two key Class I KNOTTED1-like homeobox genes that promote meristem identity in the cambium were downregulated, while an Altered Phloem Development gene that is known to promote phloem differentiation was upregulated in the mutant. In wild-type plants, LBD1 was most highly expressed in the phloem and cambial zone. Dominant-negative suppression of Pta LBD1 via translational fusion with the repressor SRDX domain caused decreased diameter growth and suppressed and highly irregular phloem development. Homology analysis showed highest similarity to an uncharacterized LBD1 gene from Arabidopsis thaliana, and we consequently named it Populus tremula × Populus alba (Pta) LBD1. Molecular characterization of the mutation through positioning of the tag and retransformation experiments shows that the phenotype is conditioned by activation of an uncharacterized gene that encodes a novel member of the LATERAL ORGAN BOUNDARIES DOMAIN (LBD) family of transcription factors. We identified and subsequently characterized an activation-tagged poplar ( Populus tremula × Populus alba) mutant with enhanced woody growth and changes in bark texture caused primarily by increased secondary phloem production. Our results indicate that overexpression of the chimeric gene OsDST-SRDX improves salt tolerance of switchgrass, a C 4 biofuel crop.Ĭhimeric REpressor gene-silencing technology (CRES-T) DST SRDX domain Salt tolerance Switchgrass.Regulation of secondary (woody) growth is of substantial economic and environmental interest but is poorly understood. The transgenic plants had also higher activities of antioxidant enzymes associated with suppressed expressing of genes in H 2O 2 homeostasis, including glutathione S-transferase (GST2, GST6), cytochrome P450, peroxidase 24 precursor, and induced expressing of CAT and SOD under salt stress to eliminate excess H 2O 2. They performed better under salt stress, had higher relative leaf water content, lower electrolyte leakage and lower malondialdehyde (MDA) content, and accumulated less Na + and more K + than WT controls. Compared to wild-type (WT) plants, OsDST-SRDX transgenic (TG) switchgrass plants showed wider leaves and thicker stems. To improve salt tolerance of switchgrass, a chimeric DROUGHT AND SALT TOLERANCE (DST) gene OsDST-SRDX was constructed using the Chimeric REpressor gene-Silencing Technology (CRES-T), and introduced into switchgrass genome by Agrobacterium-mediated transformation. To avoid competing with crops in arable land utilization, improving salt tolerance of switchgrass is required to use marginal saline land for switchgrass production. Switchgrass (Panicum virgatum L.) is a forage and model feedstock plant. Overexpression of OsDST-SRDX chimeric gene in switchgrass promotes plant growth and improves the salt tolerance of transgenic switchgrass by improving its antioxidative ability.
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