ABSTRACT
The acceleration of flowering by a long period of low temperature, vernalization, is an adaptation that ensures plants overwinter before flowering. Vernalization induces a developmental state that is mitotically stable, suggesting that it may have an epigenetic basis. The VERNALIZATION2 (VRN2) gene mediates vernalization and encodes a nuclear-localized zinc finger protein with similarity to Polycomb group (PcG) proteins of plants and animals. In wild-type Arabidopsis, vernalization results in the stable reduction of the levels of the floral repressor FLC. In vrn2 mutants, FLC expression is downregulated normally in response to vernalization, but instead of remaining low, FLC mRNA levels increase when plants are returned to normal temperatures. VRN2 function therefore stably maintains FLC repression after a cold treatment, serving as a mechanism for the cellular memory of vernalization.
Subject(s)
Arabidopsis Proteins/physiology , Arabidopsis/genetics , Carrier Proteins/physiology , Genes, Plant , MADS Domain Proteins/physiology , Nuclear Proteins/physiology , Plant Proteins/physiology , Agrobacterium tumefaciens/genetics , Amino Acid Motifs , Amino Acid Sequence , Arabidopsis/growth & development , Arabidopsis Proteins/genetics , Carrier Proteins/genetics , Chromosomes, Artificial, Yeast/genetics , Cloning, Molecular , Codon/genetics , Cosmids/genetics , DNA, Complementary/genetics , DNA-Binding Proteins , Deoxyribonuclease I/metabolism , Gene Library , Genetic Vectors/genetics , MADS Domain Proteins/antagonists & inhibitors , MADS Domain Proteins/biosynthesis , MADS Domain Proteins/genetics , Molecular Sequence Data , Nuclear Proteins/genetics , Plant Proteins/antagonists & inhibitors , Plant Proteins/biosynthesis , Plant Proteins/genetics , Protein Structure, Tertiary , RNA, Messenger/biosynthesis , RNA, Messenger/genetics , RNA, Plant/biosynthesis , RNA, Plant/genetics , Recombinant Fusion Proteins/physiology , Seasons , Sequence Alignment , Sequence Homology, Amino Acid , Temperature , Transcription Factors/chemistry , Zinc Fingers/genetics , Zinc Fingers/physiologyABSTRACT
At a certain stage in their life cycle, plants switch from vegetative to reproductive development. This transition is regulated by multiple developmental and environmental cues. These ensure that the plant switches to flowering at a time when sufficient internal resources have been accumulated and the environmental conditions are favorable. The use of a molecular genetic approach in Arabidopsis has resulted in the identification and cloning of many of the genes involved in regulating floral transition. The current view on the molecular function of these genes, their division into different genetic pathways, and how the pathways interact in a complex regulatory network are summarized.
Subject(s)
Plant Development , Plants/genetics , Genes, Plant , Meristem/growth & development , Plant Structures/growth & developmentABSTRACT
Leukemia inhibitory factor (LIF) is a mammalian cytokine that has a wide range of physiological activities, including the inhibition of differentiation of embryonic stem (ES) cells. We have used insertional mutagenesis in an attempt to isolate molecules that participate in LIF signal transduction via the LIF receptor. Using a robust screen for undifferentiated cells, we have isolated one ES cell line, Poly 27, that does not require exogenous LIF to remain undifferentiated in vitro. We present evidence that Poly 27 is not irreversibly committed to an undifferentiated phenotype, but can differentiate in vitro if cultured in the presence of chemical differentiating agents, while in syngeneic mice Poly 27 cells form tumours which are composed largely of undifferentiated cells. We have characterized the mechanism of factor independence in Poly 27, and shown it to be a result of autocrine LIF production. This LIF production is potentially the result of a mutation in a gene critically involved in regulating LIF production in ES cells.
