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1.
Acceleration of nucleic acid hybridization rate by polyethylene glycol   总被引:58,自引:0,他引:58  
The addition of polyethylene glycol to filter-bound nucleic acid hybridization greatly increases the hybridization rate. With single-stranded probes, the increase obtained with polyethylene glycol is significantly greater than that obtained with dextran sulfate. Additionally, polyethylene glycol is easier to manipulate and less expensive than dextran sulfate.  相似文献   
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Recent work in Arabis alpina, a perennial relative of Arabidopsis, has uncovered subtle differences in control of a gene that represses flowering which contributes to the polycarpic habit.  相似文献   
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For optimal survival, various environmental and endogenous factors should be monitored to determine the appropriate timing for seed germination. Light is a major environmental factor affecting seed germination, which is perceived by phytochromes. The light-dependent activation of phytochrome B (PHYB) modulates abscisic acid and gibberellic acid signaling and metabolism. Thus far, several negative regulators of seed germination that act when PHYB is inactive have been reported. However, neither positive regulators of seed germination downstream of PHYB nor a direct mechanism for regulation of the hormone levels has been elucidated. Here, we show that the histone arginine demethylases, JMJ20 and JMJ22, act redundantly as positive regulators of seed germination. When PHYB is inactive, JMJ20/JMJ22 are directly repressed by the zinc-finger protein SOMNUS. However, upon PHYB activation, JMJ20/JMJ22 are derepressed, resulting in increased gibberellic acid levels through the removal of repressive histone arginine methylations at GA3ox1/GA3ox2, which in turn promotes seed germination.  相似文献   
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Given their sessile nature, it is critical for the survival of plants to adapt to their environment. Accordingly, plants have evolved the ability to sense seasonal changes to govern developmental fates such as the floral transition. Temperature and day length are among the seasonal cues that plants sense. We recently reported that VIN3-LIKE 1 (VIL1) is involved in mediating the flowering response to both cold and day length via regulation of two related genes, FLOWERING LOCUS C (FLC) and FLOWERING LOCUS M (FLM), respectively.Key Words: flowering, vernalization, photoperiod, chromatin, histone, gene expressionVernalization renders plants competent to flower after exposure to the prolonged cold of winter.1,2 Arabidopsis exhibits facultative responses to both vernalization and photoperiod to initiate the floral transition. The facultative nature of the responses makes Arabidopsis a tractable genetic system to study these aspects of flowering time control.In Arabidopsis, vernalization creates competence to flower via silencing of the potent floral repressor, FLC, in a mitotically stable manner.3,4 Thus, the vernalization response is an environmentally induced epigenetic switch in that exposure to cold permanently affects the plants'' developmental program. This epigenetic switch is associated with increased levels of FLC chromatin methylation on Histone H3 Lys 9 and Lys 27.5,6 VERNALIZATION INSENSITIVE 3 (VIN3) plays an essential role in this switch since no modifications to FLC chromatin occur in vin3 mutants.5 Furthermore, the levels of expression of VIN3 mRNA are tightly correlated with the degree of the vernalization response.5 VIN3 encodes Plant HomeoDomain (PHD) finger-containing protein. PHD finger-containing proteins are often associated with protein complexes that are involved in chromatin remodeling.7We performed a yeast two-hybrid screen to identify potential protein partners of VIN3. VIN3-LIKE 1 (VIL1) was identified by this screen.8 VIL1 encodes a PHD finger-containing protein that is related to VIN3. As expected for proteins that are associated with VIN3, plants containing loss-of-function alleles of VIL1 do not respond to vernalization. Furthermore, no vernalization-mediated histone modifications occur at FLC in vil1 mutants similar to the situation in vin3 mutants. Thus, by yeast two hybrid and genetic analysis, VIL1 is a bona fide VIN3 partner that is required for vernalization-mediated histone modifications at FLC chromatin. Unlike VIN3, the expression of VIL1 does not change over the course of cold exposure. Rather, VIL1 mRNA levels are affected by photoperiod. VIL1 expression is significantly increased in non-inductive photoperiods (short days; SD). Consistent with this expression pattern, vil1 mutants in the Columbia accession exhibit a SD-specific late-flowering phenotype. Furthermore, VIL1 is required for attenuating expression of FLOWERING LOCUS M, a FLC-related gene, in a SD-specific manner. It is possible that the attenuation of FLM by VIL1 has a role in creating the facultative nature of photoperiod response in Arabidopsis since vil1 mutants tend towards an obligate photoperiod response (i.e., vil1 mutants often fail to flower in SD).In Arabidopsis, there are four VIN3-related genes, which we named as VIL1VIL4,8 and which have also been called VRN5 and VEL1VEL3.9 The C-terminal domain is highly conserved among these genes and was named the VIN3-Interacting Domain (VID) since it is required for protein-protein interaction between VIN3 and VIL1. The effect of cold on the expression patterns of VIN3-related genes varies. For example, VIL2 and VIL3 are induced specifically by vernalizing cold exposures whereas others such as VIL1 are, for the most part, constitutively expressed. It will be interesting to determine the functions of the remaining VIL genes.FLC is the main target for vernalization in Arabidopsis. Interestingly, FLC orthologs have not been found in vernalization-responsive varieties of cereals. However, in wheat, VRN2 appears to have a role equivalent to that of FLC in Arabidopsis.10 VRN2 encodes a ZCCT type zinc-finger protein that does not have a homolog in the Arabidopsis genome. In diploid wheat, down regulation of VRN2 is correlated with the vernalization response.11 Interestingly, wheat contains three VIN3-LIKE (VIL) genes, TmVIL1, TmVIL2 and TmVIL3.12 Furthermore, TmVIL1 is up-regulated by vernalization.12 However, whether TmVIL1 has a direct role in the vernalization-mediated repression of VRN2 in wheat has not yet been addressed. Similar to VIL1, TmVIL3 shows elevated level of expression in SD. Furthermore, VRN2 is downregulated in SD;13,14 thus there is a correlation between the induction of TmVIL genes and the downregulation of the floral repressor VRN2 similar to the VIN3/FLC and VIL1/FLM relationships (Fig. 1). Perhaps VIN3-related genes have similar roles both in Arabidopsis and in temperate wheat, but act on different target genes, possibly as a result of convergent evolution. Interestingly, the wheat gene TmVRN3 is homologous to FLOWERING LOCUS T (FT) of Arabidopsis, and TmVRN3 is repressed by TmVRN2 as FT is repressed by FLC,15 suggesting another similarity in the regulation of flowering time between Arabidopsis and temperate wheat (Fig. 1).Open in a separate windowFigure 1Proposed relationship of VIN3 family genes to the regulatory network controlling flowering time in response to environmental cues in Arabidopsis and diploid wheat (adapted from ref. 16).Although the PHD finger can be found in various eukaryotes, the VID is unique to plants. It is also noteworthy that VIN3-related genes can be found in various plant species, including rice, which does not have a vernalization response. It will be interesting to address whether the VIN3-related genes from various plant species are more broadly involved in relaying environmental signals to developmental programs.  相似文献   
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Many plant species have evolved the ability to flower in the proper season by sensing environmental cues. The prolonged cold of winter is one such cue that certain plants use to acquire competence to flower the following spring. For example, biennials and winter annuals become established in one growing season and often flower quickly in the early spring of the following year to complete their life cycles. The process by which exposure to prolonged cold establishes competence to flower is known as vernalization. Many studies, starting with the classic work of Lang and Melchers, have shown that the vernalized state can be stable; i.e. after exposure to cold has ended, competence to flower, in certain species, can persist for many months and throughout many cell divisions in the shoot apical meristem. Thus, plants can exhibit a 'memory of winter' and vernalization can result in an epigenetic switch in the classic sense of the term: a change that is stable in the absence of the inducing signal. The nature of this epigenetic switch in Arabidopsis thaliana is discussed here.  相似文献   
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Plants synchronize developmental and metabolic processes with the earth's 24-h rotation through the integration of circadian rhythms and responses to light. We characterize the time for coffee (tic) mutant that disrupts circadian gating, photoperiodism, and multiple circadian rhythms, with differential effects among rhythms. TIC is distinct in physiological functions and genetic map position from other rhythm mutants and their homologous loci. Detailed rhythm analysis shows that the chlorophyll a/b-binding protein gene expression rhythm requires TIC function in the mid to late subjective night, when human activity may require coffee, in contrast to the function of EARLY-FLOWERING3 (ELF3) in the late day to early night. tic mutants misexpress genes that are thought to be critical for circadian timing, consistent with our functional analysis. Thus, we identify TIC as a regulator of the clock gene circuit. In contrast to tic and elf3 single mutants, tic elf3 double mutants are completely arrhythmic. Even the robust circadian clock of plants cannot function with defects at two different phases.  相似文献   
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FLOWERING LOCUS M (FLM) is a MADS-domain gene that acts as an inhibitor of flowering in Arabidopsis. Here we describe the genetic interaction of FLM with genes in the photoperiod and autonomous flowering pathways. Although the sequence of FLM is most similar to that of FLC, FLM and FLC interact with different flowering pathways. It has been previously shown that flc lesions suppress the late-flowering phenotype of FRI-containing lines and autonomous-pathway mutants. However, flm lesions suppress the late-flowering phenotype of photoperiod-pathway mutants but not that of FRI-containing lines or autonomous-pathway mutants. Another MADS-domain flowering repressor with a mutant phenotype similar to FLM is SVP. The late-flowering phenotype of FLM over-expression is suppressed by the svp mutation, and an svp flm double mutant behaves like the single mutants. Thus FLM and SVP are in the same flowering pathway which interacts with the photoperiod pathway. Abbreviations: CO, CONSTANS; FLC, FLOWERING LOCUS C; FLM, FLOWERING LOCUS M; FRI, FRIGIDA; GI, GIGANTEA; LD, LUMINIDEPENDENS; SVP, SHORT VEGETATIVE PHASE; FCA is not an abbreviation  相似文献   
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