Ugt

AReference to the first publications on the isolation and characterization of the corresponding cDNA gene. bCytP450s are classified according to molecular phylogeny into numbered families ( 40 amino acid positional identity) and subfamilies designated by a letter ( 55 amino acid identity). cReference is given to the first example of isolation of a DFR cDNA that was shown to have FNR activity. dRecombinant A5GT proteins show varying degrees of anthocyanin substrate specificity. eThe nomenclature...

Genes Promoting Floral Meristem Identity Fruitfull an Unexpected Influence

A third AP1 -like gene, originally called AGL8, exists in the Arabidopsis genome (Mandel and Yanofsky, 1995a). Initial functional analysis of this gene revealed a role in fruit development and the gene was renamed FRUITFULL (FUL) (Gu et al., 1998). Mutations in the FUL gene affect the development of the valve, replum and style. It was noted, however, that in addition to its later expression, FUL is expressed early in the SAM and is upregulated on induction of flowering. Consistent with this...

Downstream Targets of Floral Organidentity Genes

Although we have a good understanding of how floral organ identity is specified by the ABC class genes and how the ABC class genes are regulated, we know far less about the events occurring downstream of these factors. Few direct targets of the ABC class transcription factors have been identified. Several types of transcriptional profiling techniques such as differential screening, subtractive hybridization, differential display and expression microarrays have been performed using transgenic...

Genetic Modification of Flower Pigmentation

Novelty is a key driver of the commercial success of ornamental crops. There is much scope to introduce novel flower colours, as some of the leading ornamental crops show only a narrow colour spectrum, whilst in others specific colours, like blue or yellow, are lacking. GM of pigment biosynthesis offers a route to colours outside the existing range, and in the long term is likely to have a major influence on ornamental breeding. Indeed, the first ornamental products from GM of flavonoid...

Introduction

Abcde Model Flower Development

Origin and diversification of angiosperms an 'abominable perplexing phenomenon' The structural diversity of multicellular organisms on our planet originated to a large extent in two major 'bursts'. During the 'Cambrian Explosion' about 540 million years ago (MYA) the body plans of (almost) all animal taxa (extant and extinct) originated within a few million years (Valentine et a ., 1999) in many respects, such as number of species, the insects became by far the most successful group of animals....

Flc

An overview of the major floral signalling pathways in Arabidopsis. The photoperiod, autonomous vernalization, gibberellin, sucrose, light quality and ambient temperature pathways activate floral-pathway integrators. The CONSTANS (CO) gene functions in the photoperiod pathway, long-day photoperiods promote flowering by circadian clock-dependent and -independent mechanisms, which control the activity of CO. FLOWERING LOCUS C (FLC) is the primary upstream target of a large number of...

References

Abdrakhamanova, A., Wang, Q.Y., Khokhlova, L. and Nick, P. (2003) Is microtubule disassembly a trigger for cold acclimation Plant & Cell Physiology 44, 676-686. Amasino, R.M. (2003) Flowering time a pathway that begins at the 3' end. Current Biology 13, R670-672. An, H., Roussot, C., Suarez-Lopez, P., Corbesier, L., Vincent, C., Pineiro, M., Hepworth, S., Mouradov, A., Justin, S., Turnbull, C. and Coupland, G. (2004) CONSTANS acts in the phloem to regulate a systemic signal that induces...

Discovery and variation

The response of plants to the daily duration of light was proposed independently by Julien Tournois and Hans Klebs at the beginning of the 20th century. It was the American physiologists Garner and Allard (1920), however, who first saw clearly that flowering and many other responses in plants could be accelerated either by long days (LDs) or by short days (SDs), depending on the plant. They were led to their discoveries by studies on 'Maryland Mammoth' variety of tobacco that failed to flower...

The circadian clock as the timing mechanism

The timing mechanism used in photoperiodism seems in most cases to be based on endogenous circadian rhythms in light sensitivity, as first postulated by Bunning (1936). He suggested that the circadian clock consisted of two half cycles, photophil and scotophil. When light was received in the scotophilic phase, the daily cycle was perceived as an LD, but the absence of light during the scotophilic phase produced an SD response. This idea was further refined by Pittendrigh and Minis (1964) to...

Sepallata Genes Work with ABC Genes to Specify Organ Identity

A significant revision of the ABC model was the addition of the class E or SEPALLATA (SEP) genes, which were first identified in tomato and petunia. Decreased expression of the TM5 gene in tomato and the FBP2 and FBP5 genes in petunia resulted in partial homeotic transformations in the second, third and fourth whorls of the flower (Angenent et al., 1994 Pnueli et al., 1994 Ferrario et al., 2003). The specific role of these genes in flower development, however, was not well defined until...

Vernalization requirement evolved independently in temperate cereals

Temperate cereals like wheat, barley, rye and oats exhibit a vernalization requirement, whereas rice and maize, which are of a more subtropical origin, do not. The analysis of vernalization requirement in cereals reveals that it involves different genes to Arabidopsis, indicating that this requirement has evolved independently. The major loci controlling vernalization requirement in the diploid wheat Triticum monococcum are VRN1 and VRN2 (in cereals the VERNALIZATION, VRN, designation applies...

Pathways to flowering in Arabidopsis

Flowering is generally regarded as a default process that will occur at some point in the plant's life. The time that a plant flowers, however, is affected by many environmental and endogenous factors and consequently there are numerous genetic pathways that are involved in the control of flowering time. These pathways interact in different ways depending upon endogenous signals and the environmental conditions thus enabling the plant to flower in the most favourable conditions. Our...

Floral diversification

The flowers of the 250,000 or so extant angiosperm species on Earth vary in many different ways such as the identity, number, arrangement and shape of floral organs, and the symmetry of the flower as a whole (see, e.g. Fig. 6.1). These differences are all of great potential interest for future evo-devo studies aiming at understanding the developmental genetic basis of floral biodiversity. Mutants in model plants exist for all of these characters. However, detailed studies have been carried out...

Categories of Flower Senescence

Several categories of flower senescence have been used to describe how a flower senesces. Three categories can be distinguished in the literature (i) age related versus pollination induced (ii) ethylene sensitive versus ethylene insensitive and (iii) abscised versus persistent petals. These are somewhat artificial divisions but are based on distinct morphological, biochemical or molecular changes associated with each type of senescence. Age related versus pollination induced Pollination is the...

Flower Origin

Since the identity of floral organs is specified by conserved floral organ-identity genes, clarifying the phylogeny of these genes and their protein products may provide us with valuable insights into the evolution of flowers (for reviews, see Theissen and Saedler, 1995 Theissen et al., 2000, 2002). Analysis of numerous MADS box genes from mosses and ferns suggested that orthologues of floral homeotic genes are absent in non-seed plants (for a review, see Theissen et al., 2000). However,...

Biochemical Signalling to the Shoot Apical Meristem

Biochemical Signaling Flowering

Phytohormones influence many diverse developmental processes ranging from seed germination to root, shoot and flower formation. Mutational analysis using Arabidopsis has been instrumental in determining the individual components of specific hormone signal transduction pathways. While no hormone transduction pathway is completely understood, the genes identified to date suggest that simple molecular rules can be established to explain how plant hormone signals are transduced (McCourt, 1999 Hay...

Second Messengers In Cytokinin Signalling

Fig. 3.2. (A) gibberellin (GA) signalling pathway that regulates flowering in Arabidopsis. Activation of a hypothetical transmembrane receptor by GA inhibits repressors of GA signalling. These repressors are encoded by the DELLA proteins. The SPINDLY (SPY) gene also represses GA signalling and genetically acts upstream of RGA and GAI. It may act to promote the activity of GAI RHA RGL by N-acetylglucosamine (GlcNAc) modification, in which case GA signalling may inhibit GAI RGA RGL by repressing...

Genes Promoting Floral Meristem Identity Apetala1 and Cauliflower the Supporting Cast

As suggested above, the fact that later-arising meristems on Ify inflorescences adopt a more floral character suggests that other genes, which are activated later than LFY, can partially compensate for the lack of LFY activity and confer FM identity. API was a prime candidate for such a gene, since the flowers formed in apl mutants also show inflorescence characteristics (Irish and Sussex, 1990) (Fig. 4.2). LFY is expressed in the periphery of the SAM at about the time of the switch to IM. A...

Timing of Senescence the Opening

The fact that petal senescence is under genetic control is well established. Genotypes with varying flower longevity have been identified in Dianthus caryophyllus Wu et al., 1989 Brandt and Woodson, 1992 , Dianthus barbatus Friedman et al., 2001 , Antirrhinum majus Schroeder and Stimart, 2001 , Petunia x hybrida Porat et al., 1993, Krahl and Randle, 1999 , Lilium longiflorum van der Meulen-Muisers etal., 1998 , Gerbera x hybrida Wernett et al., 1996 and Hatoria x graeseri Easter cactus Karle...

Mechanistic Aspects of Floral Signal Transduction

We are rapidly gaining insight into the genetic make-up that comprises the major signalling routes employed by plants for flowering, the continued use of forward and reverse genetics and global expression strategies will add new elements to the skeletal networks already established. Detailed analysis of specific gene to gene interactions is now starting to reveal some of the mechanisms and strategies that are employed to convey the signal message within the cell and from cell to cell. Control...

Regulation of Senescence

Ethylene-sensitive flower senescence has received most attention by far in studies of flower longevity, most likely because a number of highly valuable flower crops fall into this category Reid and Wu, 1992 . Ethylene measurements are relatively easy to make, and the clear link between senescence and ethylene production in ethylene-sensitive plants has contributed to the increased attention paid to them Borochov and Woodson, 1989 van Altvorst and Bovy, 1995 . However, it should be clear that...