FLOWERING LOCUS T (FT), which acts in parallel with the meristem-identity gene LEAFY (LFY) to induce flowering of Arabidopsis, was isolated by activation tagging. Like LFY, FT acts partially downstream of CONSTANS (CO), which promotes flowering in response to long days. Unlike many other floral regulators, the deduced sequence of the FT protein does not suggest that it directly controls transcription or transcript processing. Instead, it is similar to the sequence of TERMINAL FLOWER 1 (TFL1), an inhibitor of flowering that also shares sequence similarity with membrane-associated mammalian proteins.

https://science.sciencemag.org/content/sci/286/5446/1962.full.pdf

Activation tagging of the floral inducer FT.

Plant microRNAs (miRNAs) affect only a small number of targets with high sequence complementarity, while animal miRNAs usually have hundreds of targets with limited complementarity. We used artificial miRNAs (amiRNAs) to determine whether the narrow action spectrum of natural plant miRNAs reflects only intrinsic properties of the plant miRNA machinery or whether it is also due to past selection against natural miRNAs with broader specificity. amiRNAs were designed to target individual genes or groups of endogenous genes. Like natural miRNAs, they had varying numbers of target mismatches. Previously determined parameters of target selection for natural miRNAs could accurately predict direct targets of amiRNAs. The specificity of amiRNAs, as deduced from genome-wide expression profiling, was as high as that of natural plant miRNAs, supporting the notion that extensive base pairing with targets is required for plant miRNA function. amiRNAs make an effective tool for specific gene silencing in plants, especially when several related, but not identical, target genes need to be downregulated. We demonstrate that amiRNAs are also active when expressed under tissue-specific or inducible promoters, with limited nonautonomous effects. The design principles for amiRNAs have been generalized and integrated into a Web-based tool (http://wmd.weigelworld.org).

/pdf/highly-specific-gene-silencing-by-artificial-micrornas-in-46188e4r0f.pdf

Highly specific gene silencing by artificial microRNAs in Arabidopsis.

https://dspace.library.uu.nl/bitstream/handle/1874/21099/scheres_99_anauxindependentdistal.pdf;sequence=2

An auxin-dependent distal organizer of pattern and polarity in the Arabidopsis root

Flowering of Arabidopsis is regulated by several environmental and endogenous signals An important integrator of these inputs is the FLOWERING LOCUS T (FT) gene, which encodes a small, possibly mobile protein A primary response to floral induction is the activation of FT RNA expression in leaves Because flowers form at a distant site, the shoot apex, these data suggest that FT primarily controls the timing of flowering Integration of temporal and spatial information is mediated in part by the bZIP transcription factor FD, which is already expressed at the shoot apex before floral induction A complex of FT and FD proteins in turn can activate floral identity genes such as APETALA1 (AP1)

https://science.sciencemag.org/content/sci/309/5737/1056.full.pdf

Integration of spatial and temporal information during floral induction in Arabidopsis.

https://www.ndsu.edu/pubweb/~mcclean/plsc731/homework/wang-et-al-miR156-regulated-SPL-transcription-factors-define-an-endogenous-flowering-pathway-in-Arabidopsis-thaliana.pdf

miR156-Regulated SPL Transcription Factors Define an Endogenous Flowering Pathway in Arabidopsis thaliana

https://digital.library.unt.edu/ark:/67531/metadc779593/m2/1/high_res_d/821977.pdf

A molecular link between stem cell regulation and floral patterning in Arabidopsis.

The initial steps of flower development involve two classes of consecutively acting regulatory genes. Meristem-identity genes, which act early to control the initiation of flowers, are expressed throughout the incipient floral primordium. Homeotic genes, which act later to specify the identity of individual floral organs, are expressed in distinct domains within the flower. The link between the two classes of genes has remained unknown so far. Here we show that the meristem-identity gene LEAFY has a role in controlling homeotic genes that is separable from its role in specifying floral fate. On the basis of our observation that LEAFY activates different homeotic genes through distinct mechanisms, we propose a genetic framework for the control of floral patterning.

A genetic framework for floral patterning.

The patterned expression of floral homeotic genes in Arabidopsis depends on the earlier action of meristem-identity genes such as LEAFY, which encodes a transcription factor that determines whether a meristem will generate flowers instead of leaves and shoots. The LEAFY protein, which is expressed throughout the flower, participates in the activation of homeotic genes, which are expressed in specific regions of the flower. Analysis of a LEAFY-responsive enhancer in the homeotic gene AGAMOUS indicates that direct interaction of LEAFY with this enhancer is required for its activity in plants. Thus, LEAFY is a direct upstream regulator of floral homeotic genes.

https://science.sciencemag.org/content/sci/285/5427/585.full.pdf

Activation of a Floral Homeotic Gene in Arabidopsis

In Arabidopsis thaliana, cis-regulatory sequences of the floral homeotic gene AGAMOUS (AG) are located in the second intron. This 3-kb intron contains binding sites for two direct activators of AG, LEAFY (LFY) and WUSCHEL (WUS), along with other putative regulatory elements. We have used phylogenetic footprinting and the related technique of phylogenetic shadowing to identify putative cis-regulatory elements in this intron. Among 29 Brassicaceae species, several other motifs, but not the LFY and WUS binding sites identified previously, are largely invariant. Using reporter gene analyses, we tested six of these motifs and found that they are all functionally important for the activity of AG regulatory sequences in A. thaliana. Although there is little obvious sequence similarity outside the Brassicaceae, the intron from cucumber AG has at least partial activity in A. thaliana. Our studies underscore the value of the comparative approach as a tool that complements gene-by-gene promoter dissection but also demonstrate that sequence-based studies alone are insufficient for a complete identification of cis-regulatory sites.

https://digital.library.unt.edu/ark:/67531/metadc779813/m2/1/high_res_d/821972.pdf

Regulatory elements of the floral homeotic gene AGAMOUS identified by phylogenetic footprinting and shadowing

The plant-specific transcription factor LEAFY controls general aspects of the life cycle in a basal plant, the moss Physcomitrella patens. In contrast, LEAFY has more specialized functions in angiosperms, where it specifically induces floral fate during the reproductive phase. This raises the question of a concomitant change in the biochemical function of LEAFY during the evolution of land plants. We report that the DNA binding domain of LEAFY, although largely conserved, has diverged in activity. On the contrary, other, more rapidly evolving portions of the protein have few effects on LEAFY activity.

https://science.sciencemag.org/content/sci/308/5719/260.full.pdf

Maximilian A. Busch

Papers

A molecular link between stem cell regulation and floral patterning in Arabidopsis.

A genetic framework for floral patterning.

Activation of a Floral Homeotic Gene in Arabidopsis

Regulatory elements of the floral homeotic gene AGAMOUS identified by phylogenetic footprinting and shadowing

The floral regulator LEAFY evolves by substitutions in the DNA binding domain.