The molecular genetics of vernalization, defined as the promotion of flowering by cold treatment, is still poorly understood in cereals. To better understand this mechanism, we cloned and characterized a gene that we named TaVRT-1 (wheat [Triticum aestivum] vegetative to reproductive transition-1). Molecular and sequence analyses indicated that this gene encodes a protein homologous to the MADS-box family of transcription factors that comprises certain flowering control proteins in Arabidopsis. Mapping studies have localized this gene to the Vrn-1 regions on the long arms of homeologous group 5 chromosomes, regions that are associated with vernalization and freezing tolerance (FT) in wheat. The level of expression of TaVRT-1 is positively associated with the vernalization response and transition from vegetative to reproductive phase and is negatively associated with the accumulation of COR genes and degree of FT. Comparisons among different wheat genotypes, near-isogenic lines, and cereal species, which differ in their vernalization response and FT, indicated that the gene is inducible only in those species that require vernalization, whereas it is constitutively expressed in spring habit genotypes. In addition, experiments using both the photoperiod-sensitive barley (Hordeum vulgare cv Dicktoo) and short or long day de-acclimated wheat revealed that the expression of TaVRT-1 is also regulated by photoperiod. These expression studies indicate that photoperiod and vernalization may regulate this gene through separate pathways. We suggest that TaVRT-1 is a key developmental gene in the regulatory pathway that controls the transition from the vegetative to reproductive phase in cereals.Freezing tolerance (FT) in cereals is dependent upon a highly integrated system of structural, regulatory, and developmental genes. The development of maximum low-temperature (LT) tolerance is known to be associated with two important developmentally controlled adaptive features (Mahfoozi et al., 2001a). The first is a vernalization requirement that delays heading by postponing the transition from the vegetative to the reproductive phase. The second is a photoperiod requirement that allows the plant to flower only when exposed to optimal inducing conditions. Time sequence studies have shown that LT-induced gene expression is also developmentally regulated (Fowler et al., 1996a(Fowler et al., , 1996b. In these studies, transition from the vegetative to the reproductive growth phase can be perceived as a critical switch that initiates the down-regulation of LTinduced genes (Fowler et al., 1996a(Fowler et al., , 1996b(Fowler et al., , 2001Mahfoozi et al., 2001aMahfoozi et al., , 2001b. As a result, full expression of cold hardiness genes only occurs in the vegetative phase, and plants in the reproductive phase have a limited ability to cold acclimate. In addition, plants that are still in the vegetative phase have the ability to re-acclimate following periods of exposure to warm temperatures, whereas plants in the reproductive phase ...

Expression of the acidic dehydrin gene wcor410 was found to be associated with the development of freezing tolerance in several Gramineae species. This gene is part of a family of three homologous members, wcor410 , wcor410b , and wcor410c , that have been mapped to the long arms of the homologous group 6 chromosomes of hexaploid wheat. To gain insight into the function of this gene family, antibodies were raised against the WCOR410 protein and affinity purified to eliminate cross-reactivity with the WCS120 dehydrin-like protein of wheat. Protein gel blot analyses showed that the accumulation of WCOR410 proteins correlates well with the capacity of each cultivar to cold acclimate and develop freezing tolerance. Immunoelectron microscope analyses revealed that these proteins accumulate in the vicinity of the plasma membrane of cells in the sensitive vascular transition area where freeze-induced dehydration is likely to be more severe. Biochemical fractionation experiments indicated that WCOR410 is a peripheral protein and not an integral membrane protein. These results provide direct evidence that a subtype of the dehydrin family accumulates near the plasma membrane. The properties, abundance, and localization of these proteins suggest that they are involved in the cryoprotection of the plasma membrane against freezing or dehydration stress. We propose that WCOR410 plays a role in preventing the destabilization of the plasma membrane that occurs during dehydrative conditions.

Exposure of plants to low temperature (LT) produces a myriad of measurable changes in morphological, biochemical, and physiological characters that are often highly correlated with plant cold tolerance. These complicated responses have made it difficult to separate cause‐and‐effect adjustments to LT, emphasizing the need for a descriptive framework for the integration of current knowledge so that research efforts can be better focused. The objective of this study was to construct a functional model that complies with the known LT responses of cereals so production risks, cause‐and‐effect processes, and genetic theories can be systematically investigated. In the model, a series of equations describe acclimation, dehardening, and damage due to LT stress. A modular design permits modification and allows the model to be interfaced with other simulation models that input or compute daily measurements of soil temperature and phonological development. LT tolerance is estimated on a daily basis relative to phenological stage and the input of a genetic coefficient is required. Operation of the model is consistent with recent interpretation of LT‐gene regulation and it is especially sensitive to the switching signals that down‐regulate LT‐gene expression in plants maintained for long periods of time in the optimum temperature range for cold acclimation. Simulation studies have also shown that small differences in cultivar genetic potential translate into large differences in LT tolerance when the cumulative effects of LT stress enter the critical range for overwinter survival. The model has been field validated for cereals overwintered in Saskatchewan, Canada, but it also has potential application in the simulation of LT responses of a wide range of species and climates.

Expression of the acidic dehydrin gene wcor410 was found to be associated with the development of freezing tolerance in several Gramineae species. This gene is part of a family of three homologous members, wcor410, wcor410b, and wcor410c, that have been mapped to the long arms of the homologous group 6 chromosomes of hexaploid wheat. To gain insight into the function of this gene family, antibodies were raised against the WCOR410 protein and affinity purified to eliminate cross-reactivity with the WCS120 dehydrin-like protein of wheat. Protein gel blot analyses showed that the accumulation of WCOR410 proteins correlates well with the capacity of each cultivar to cold acclimate and develop freezing tolerance. Immunoelectron microscope analyses revealed that these proteins accumulate in the vicinity of the plasma membrane of cells in the sensitive vascular transition area where freeze-induced dehydration is likely to be more severe. Biochemical fractionation experiments indicated that WCOR410 is a peripheral protein and not an integral membrane protein. These results provide direct evidence that a subtype of the dehydrin family accumulates near the plasma membrane. The properties, abundance, and localization of these proteins suggest that they are involved in the cryoprotection of the plasma membrane against freezing or dehydration stress. We propose that WCOR410 plays a role in preventing the destabilization of the plasma membrane that occurs during dehydrative conditions.