Plant development can be divided into two phases; a vegetative and a reproductive phase. During the vegetative phase the main shoot grows and produces leaves and further side shoots, known as lateral shoots. As the plant enters the reproductive phase it begins to produce flowers that are composed of several distinct organ types. The various lateral organs of the adult plant are not formed during embryogenesis. Differentiation is continuous throughout the lifetime of the plant and positional information must therefore be generated de novo. The mechanisms which initiate and coordinate this are not yet clear. In contrast, there has been a rapid accumulation of knowledge concerning the floral developmental programme which is governed by a set of transcription factors named by their common DNA-binding domain, the MADS box. Genetic and molecular studies with two species, Arabidopsis thaliana and Antirrhinum majus, indicate common regulatory mechanisms underlying floral organ differentiation, summarised in the widely accepted ABC model. This chapter will describe and critically examine this model after a brief introduction to processes that precede flower formation.
A transformation and regeneration protocol for Antirrhinum majus that allows recovery of transgenic plants within seven months is described.Four different lines transformed with three different constructs have been tested for transformation frequency and regeneration capacity.Regenerated plants were phenotypically indistinguishable from wild-type plants and a GUS reporter gene under the control of the CaMV 35S promoter could be expressed in all tested organs of the plant, including leaves, roots and floral organs.The transgene was heritable through both male and female gametes.
Abstract To increase the utility of Antirrhinum for genetic and evolutionary studies, we constructed a molecular linkage map for an interspecific hybrid A. majus × A. molle. An F2 population (n = 92) was genotyped at a minimum of 243 individual loci. Although distorted transmission ratios were observed at marker loci throughout the genome, a mapping strategy based on a fixed framework of codominant markers allowed the loci to be placed into eight robust linkage groups consistent with the haploid chromosome number of Antirrhinum. The mapped loci included 164 protein-coding genes and a similar number of unknown sequences mapped as AFLP, RFLP, ISTR, and ISSR markers. Inclusion of sequences from mutant loci allowed provisional alignment of classical and molecular linkage groups. The total map length was 613 cM with an average interval of 2.5 cM, but most of the loci were aggregated into clusters reducing the effective distance between markers. Potential causes of transmission ratio distortion and its effects on map construction were investigated. This first molecular linkage map for Antirrhinum should facilitate further mapping of mutations, major QTL, and other coding sequences in this model genus.
In plants, flowering is triggered by endogenous and environmental signals. CONSTANS (CO) promotes flowering of Arabidopsis in response to day length. Four early target genes of CO were identified using a steroid-inducible version of the protein. Two of these genes, SUPPRESSOR OF OVEREXPRESSION OF CO 1 ( SOC1 ) and FLOWERING LOCUS T ( FT ), are required for CO to promote flowering; the others are involved in proline or ethylene biosynthesis. The SOC1 and FT genes are also regulated by a second flowering-time pathway that acts independently of CO. Thus, early target genes of CO define common components of distinct flowering-time pathways.
ABSTRACT The identity and developmental pattern of the four organ types constituting the flower is governed by three developmental functions, A, B and C, which are defined by homeotic genes and established in two adjacent whorls. In this report we morphologically and genetically characterise mutants of two genes, STYLOSA (STY) and FISTULATA (FIS) which control floral homeotic meristem- and organ-identity genes and developmental events in all floral whorls. The morphology of the reproductive organs in the first and second whorls of sty fis double mutant flowers indicate that the two genes are part of the mechanism to prevent ectopic expression of the C-function in the perianth of wild-type flowers. This is verified by the detection of the expansion of the expression domain of the class C gene PLENA (PLE) towards the perianth. Interestingly, in the second whorl of sty and fis mutants, spatial differences in stamenoid features and in the pattern of ectopic expression of the PLE gene were observed. This suggests that, with respect to the negative control of PLE, petals are composed of two regions, a lateral and a central one. Mutation in ple is epistatic to most of the sty/fis-related homeotic defects. PLE, however, is not the primary target of STY/FIS control, because dramatic reduction of expression of FIMBRIATA, meristem identity genes (FLORICAULA and SQUAMOSA) and of class B organ identity genes (GLOBOSA) occur before changes in the PLE expression pattern. We propose that STY/FIS are hierarchically high-ranking genes that control cadastral component(s) of the A-function. SQUAMOSA as a potential target of this control is discussed. Retarded growth of second whorl organs, subdivision of third whorl primordia and the failure to initiate them in sty/fis mutants may be mediated by the FIMBRIATA gene.
The expression of the Antirrhinum gene FIL2 is affected in mutants of the homeoti¢ transcription factor DEFIClENS.Northern and Western blot analyses showed that FIL2 in wild-type Antirrhinum flowers is expressed weakly in the petals and more abundantly in the reproductive organs; the gene is active in the filaments and anthers of stamens, and in the stigma and transmitting tissue of the carpels.The FIL2 protein is glycosylated with high mannose type glycan chains and is located in the middle lamella of the extracellular matrix.The amino acid sequence contains 10 tandem repeats, the composition of which is similar to the Leucine-Rich Repeat (LRR) motif found in mammals, Drosophila and yeast.The poseiblity that FIL2 might be a component of a cellular signalling mechanism, involving LRR-medlated protein-protein interactions is discussed.
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