ABSTRACT
The shoot apical meristem (SAM) is responsible for forming most of the above-ground portion of the plant. We sought to isolate regulatory genes expressed in the Arabidopsis SAM by screening a Brassica oleracea (cauliflower) meristem cDNA library with the homeobox fragment from the maize Knotted-1 (Kn1) gene. We isolated and characterized the corresponding clone, Merihb1, from Arabidopsis. Analysis shows that the predicted MERIHB1 protein exhibits strong homology to KN1 and RS1 from maize, SBH1 from soybean, and KNAT1 and KNAT2 from Arabidopsis. Merihb1 is highly expressed in mRNA from cauliflower meristems and also accumulates in stem and flower mRNA. Based on the similarity of the Merihb1 and Kn1 sequences, expression patterns, and in situ hybridizations, we suggest that Merihb1 represents an Arabidopsis homologue of the maize Kn1 gene.
Subject(s)
Arabidopsis Proteins , Arabidopsis/genetics , Genes, Homeobox , Genes, Plant , Homeodomain Proteins/genetics , Plant Proteins/genetics , Amino Acid Sequence , Base Sequence , Gene Expression Regulation, Plant , Molecular Sequence Data , RNA, Messenger/genetics , Sequence Alignment , Sequence Homology, Amino AcidABSTRACT
In plant development, leaf primordia are formed on the flanks of the shoot apical meristem in a highly predictable pattern. The cells that give rise to a primordium are sequestered from the apical meristem. Maintenance of the meristem requires that these cells be replaced by the addition of new cells. Despite the central role of these activities in development, the mechanism controlling and coordinating them is poorly understood. These processes have been characterized in the Arabidopsis mutant forever young (fey). The fey mutation results in a disruption of leaf positioning and meristem maintenance. The predicted FEY protein shares significant homology to a nodulin and limited homology to various reductases. It is proposed that FEY plays a role in communication in the shoot apex through the modification of a factor regulating meristem development.
Subject(s)
Arabidopsis Proteins , Arabidopsis/genetics , Genes, Plant , Oxidoreductases/genetics , Amino Acid Sequence , Arabidopsis/growth & development , Base Sequence , Blotting, Southern , Cloning, Molecular , Consensus Sequence , DNA Primers , DNA, Plant/isolation & purification , Gene Expression , Genomic Library , Molecular Sequence Data , Oxidoreductases/biosynthesis , Plant Leaves , Polymerase Chain Reaction , Sequence Homology, Amino AcidABSTRACT
Vegetative development in the Arabidopsis shoot apex follows both sequential and repetitive steps. Early in development, the young vegetative meristem is flat and has a rectangular shape with bilateral symmetry. The first pair of leaf primordia is radially symmetrical and is initiated on opposite sides of the meristem. As development proceeds, the meristem changes first to a bilaterally symmetrical trapezoid and then to a radially symmetrical dome. Vegetative development from the domed meristem continues as leaves are initiated in a repetitive manner. Abnormal development of the vegetative shoot apex is described for a number of mutants. The mutants we describe fall into at least three classes: (1) lesions in the shoot apex that do not show an apparent alteration in the shoot apical meristem, (2) lesions in the apical meristem that also (directly or indirectly) alter leaf primordia, and (3) lesions in the apical meristem that alter meristem size and leaf number but not leaf morphology. These mutations provide tools both to genetically analyze vegetative development of the shoot apex and to learn how vegetative development influences floral development.
