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Background: Dormancy of buds is a critical developmental process that allows perennial plants to survive extreme seasonal variations in climate. Dormancy transitions in underground crown buds of the model herbaceous perennial weed leafy spurge were investigated using a 23 K element cDNA microarray. These data represent the first large-scale transcriptome analysis of dormancy in underground buds of an herbaceous perennial species. Crown buds collected monthly from August through December, over a five year period, were used to monitor the changes in the transcriptome during dormancy transitions.

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DORMANCY ASSOCIATED MADS-BOX (DAM) genes are related to AGAMOUS-LIKE 24 and SHORT VEGETATIVE PHASE genes of arabidopsis and are differentially regulated coordinately with endodormancy induction and release in buds of several perennial plant species. DAM genes were first shown to directly impact endodormancy in peach where a deletion of a series of DAM resulted in loss of endodormancy induction. We have cloned and characterized several MADS box genes from the model perennial weed leafy spurge. Leafy spurge DAM genes are preferentially expressed in shoot tips and buds in response to cold temperatures and day length in a manner that is relative to the level of endodormancy induced by various environmental conditions. Over-expression of one DAM gene in arabidopsis delays flowering. Additionally, we show that at least one DAM gene is differentially regulated by chromatin remodeling. Comparisons of the DAM gene promoters between poplar and leafy spurge have identified several conserved sequences that may be important for their expression patterns in response to dormancy-inducing stimuli.

Seed dormancy has been associated with red grain color in cereal crops for a century. The association was linked to qSD7-1/qPC7, a cluster of quantitative trait loci for seed dormancy/pericarp color in weedy red rice. This research delimited qSD7-1/qPC7 to the Os07g11020 or Rc locus encoding a basic helix-loop-helix family transcription factor by intragenic recombinants and provided unambiguous evidence that the association arises from pleiotropy. The pleiotropic gene expressed in early developing seeds promoted expression of key genes for biosynthesis of abscisic acid (ABA), resulting in an increase in accumulation of the dormancy-inducing hormone; activated a conserved network of eight genes for flavonoid biosynthesis to produce the pigments in the lower epidermal cells of the pericarp tissue; and enhanced seed weight. Thus, the pleiotropic locus most likely controls the dormancy and pigment traits by regulating ABA and flavonoid biosynthetic pathways, respectively. The dormancy effect could be eliminated by a heat treatment, but could not be completely overcome by gibberellic acid or physical removal of the seed maternal tissues. The dormancy-enhancing alleles differentiated into two groups basically associated with tropical and temperate ecotypes of weedy rice. Of the pleiotropic effects, seed dormancy could contribute most to the weed adaptation. Pleiotropy prevents the use of the dormancy gene to improve resistance of white pericarp cultivars against pre-harvest sprouting through conventional breeding approaches. SEEDS acquire primary dormancy during development to enhance adaptation of wild species to diverse environments by distributing germination over time and space. Domestication tends to reduce dormancy by selection for rapid, uniform germination (Harlan et al. 1973). Differentiation in seed dormancy between cereal crops and wild relatives has been associated with seed morphologies (Nilsson-Ehle 1914;Johnson 1935) and quantitative trait loci (QTL). Cloning of validated dormancy loci provides in-depth insights into regulatory mechanisms underlying natural variation in this adaptive or domestication-related trait (Bentsink et al. 2006;Sugimoto et al. 2010).Weedy rice refers to Oryza spp., which competes with cultivated rice (Oryza sativa L. and O. glaberrima Steud.) from tropical to temperate areas (Oka 1988;Delouche et al. 2007). The most persistent type of weedy rice is red rice, which is characterized by a red pericarp color. Red rice has strong seed dormancy (Cohn and Hughes 1981;Noldin et al. 2006). Genetic analysis has associated pericarp color with seed dormancy in red rice (Gu et al. 2005a).This association was first reported for wheat (Triticum aestivum L.), where red grain genotypes were more dormant than the white ones, and this morphology has been used to select cultivars for resistance to pre-harvest sprouting (NilssonEhle 1914;Flintham 2000). However, it remains unknown if the association in rice, wheat, and other crops arises from a tight linkage between genes for these two trai...

Crown buds of field-grown leafy spurge ( Euphorbia esula L.) were examined to determine relationships between carbohydrate metabolism and gene expression throughout para-, endo-, and eco-dormancy during the transition from summer, autumn, and winter, respectively. The data indicates that endo-dormancy plays a role in preventing new shoot growth during the transition from autumn to winter. Cold temperature was involved in breaking endodormancy, inducing flowering competence, and inhibiting shoot growth. An inverse relationship developed between starch and soluble sugar (mainly sucrose) content in buds during the shift from para-to endo-dormancy, which continued through eco-dormancy. Unlike starch content, soluble sugars were lowest in crown buds during para-dormancy but increased over two-to three-fold during the transition to endo-dormancy. Several genes ( AGPase , HK , SPS , SuSy , and UGPase ) coding for proteins involved in sugar metabolism were differentially regulated in conjunction with welldefined phases of dormancy in crown buds. Marker genes for S-phase progression, cell wall biochemistry, or responsive to auxin were also differentially regulated during transition from para-, endo-, and eco-dormancy. The results were used to develop a model showing potential signalling pathways involved in regulating seasonal dormancy status in leafy spurge crown buds.

Antioxidant metabolites in eastem white pine (Pinus strobus L.) needles increased two-to fourfold from the summer to the winter season. Antioxidant enzymes in needle tissue increased between 2-and 122-fold during this same period. These seasonal changes were determined by monitoring ascorbate and glutathione concentrations and the activity of ascorbate peroxidase, glutathione reductase (GR), and superoxide dismutase. Levels of antioxidant metabolites and enzymes were observed always to be lowest during the summer, or active growing season, and highest during the winter, or dormant season. These data correlated well with the thermal kinetic window for purified GR obtained from summer needles. The minimum, apparent KmDm for two isoforms of GR (GRA and GRo) occurred at 5 and 10°C, respectively. The upper limit of the thermal kinetic window (200% of the minimum K.) for GRA and GRB was 20 and 250C, respectively, indicating that needle temperatures exceeding 250C may result in impairment of antioxidant metabolism. The needle content and kinetic properties of GR, the increased activities of other enzymes, and the high substrate concentrations observed during the winter are consistent with the protective function this pathway may provide against photooxidative, winter injury.

The 70-kD heat-shock proteins (HSP70s) are encoded by a multigene family in eukaryotes. In plants, the 70-kD heat-shock cognate (HSC70) proteins are located in organellar and cytosolic compartments of cells in most tissues. Previous work has indicated that HSC7O proteins of spinach (Spinacia oleracea) are adively synthesized during cold-acclimating conditions. We have isolated, sequenced, and characterized cDNA and genomic clones for the endoplasmic reticulum (ER) luminal HSC70 protein (immunoglobulin heavy chain-binding protein; BiP) of spinach. The spinach ERluminal HSC70 is a constitutively expressed gene consisting of eight exons. Spinach BiP mRNA appears to be up-regulated during cold acclimation but is not expressed during water stress or heat shock. In contrast to the differential regulation of mRNA, the ERluminal HSC70 protein levels remain constant in response to various environmental stresses. Two other members of the spinach 70-kD heat-shock (HS70) multigene family also show differential expression in response to a variety of environmental stresses. A constitutively expressed cytosolic HSC70 protein in spinach appears also to be up-regulated in response to both cold-acclimating and heat-shock treatments. Spinach also contains a cold-shockinduced HS70 gene that is not expressed during heat shock or water stress. Since HSP70s are considered to be involved with the chaperoning and folding of proteins, the data further support the concept that they may be important for maintaining cellular homeostasis and proper protein biogenesis during cold acclimation of spinach.HSP70s are a ubiquitous group of evolutionarily conserved 70-kD proteins (Craig, 1989) encoded by a multigene family in eukaryotes and by a single gene, dnaK, in Escherichia coli. In yeast, nine HS70 genes have been identified and subdivided into four subgroups of which members of severa1 subgroups are considered essential for growth under various conditions (Craig, 1989). HS70 genes have been further classified into two groups: (a) cognate (HSC70) genes, which are expressed under normal growth conditions, frequently contain introns and are not strongly induced by heat shock and (b) those that are not expressed under normal conditions