TaVRT-1, a Putative Transcription Factor Associated with Vegetative to Reproductive Transition in Cereals

Abstract

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 ...

Putting genes into genetic coefficients

“…As mentioned previously, Pugsley (1983) and White and Hoogenboom (2003) have suggested that wheat phenology could be largely explained by genes controlling plant height (Rht), photoperiod (Ppd), and vernalization (Vrn). Certainly progress has been made in mapping (Laurie, 1997;Shah et al, 1999;Kato et al, 1999;Sourdille et al, 2000;Iwaki et al, 2002;Toth et al, 2003) and cloning (Danyluk et al, 2003;Peng et al, 1999;Trevaskis et al, 2003;Yan et al, , 2004 these genes. In addition, some of the necessary information on the physiological aspects of these genes may be obtained from other genera.…”

Short Vegetative Phase-Like MADS-Box Genes Inhibit Floral Meristem Identity in Barley

“…VRN1 encodes an APETALA1 (AP1)-like MADS-box gene that is induced by exposure to long periods of cold and promotes the floral transition (Danyluk et al, 2003;Trevaskis et al, 2003;Yan et al, 2003). It is not known how cold causes activation of VRN1 expression during vernalization.…”

“…The induction of the floral transition by vernalization is mediated by the VRN1 gene in winter cereals and related grass species such as Lolium perenne (Danyluk et al, 2003;Trevaskis et al, 2003;Yan et al, 2003;Andersen et al, 2006). VRN1 encodes an APETALA1 (AP1)-like MADS-box gene that is induced by exposure to long periods of cold and promotes the floral transition (Danyluk et al, 2003;Trevaskis et al, 2003;Yan et al, 2003).…”

Identification of the VERNALIZATION 4 gene reveals the origin of spring growth habit in ancient wheats from South Asia

“…Wheat adaptation to different latitudes and planting dates is mainly associated with natural variation in the photoperiod gene PPD1 that promotes flowering under long days (4)(5)(6) and in the vernalization gene VRN1 that modulates the requirement of long exposures to cold temperatures (vernalization) to induce flowering (7)(8)(9). The photoperiod and vernalization pathways converge at the regulation of FT1 (= VRN3 in wheat) (10), which encodes a mobile protein that travels from leaves to the shoot apical meristem (SAM) (11,12).…”

“…VRN1 is a MADS-box (MCM1/AGAMOUS/DEFICIENS/SRF) transcription factor homologous to the Arabidopsis meristem identity gene APETALA 1 (7)(8)(9), and its activation by vernalization (16) or by FT1 (14) accelerates the transition of the SAM from the vegetative to the reproductive phase. Wheat varieties carrying the ancestral VRN1 allele have a strong vernalization requirement and are classified as "winter wheats."…”