Characterization of a gene transcribed in the L2 and L3 layers of the tobacco shoot apical meristem

The concept of the eudicot shoot apical meristem as it applies to four Spiraea (Rosaceae), one Mentha (Lamiaceae) and one Euonymus (Celastraceae) cultivars based on chimeric analysis

BACKGROUND AND AIMS

Eversporting eudicots were sought to see if they behave like gymnosperms. Behaviour of eversporting gymnosperm chimeras indicates a single apical cell is present in SAM and it would be of interest to see if eudicot chimeras have the same behaviour.

METHODS

Four eversporting spireas, the pineapple mint and the Silver King euonymus were inspected for the fate of the yellow (mutant)-green (wild type) chimeras.

KEY RESULTS

As with gymnosperms, unstable eudicot chimeras in the four spireas, the pineapple mint and the Silver King euonymus became stable yellow about 80 % or more of the time and 20 % or less became stable green.

CONCLUSIONS

The statistically significant preponderance of chimeric fates becoming all yellow suggests that a single apical cell resides in the yellow tunica. As with gymnosperms, descendent cells of the yellow replacement corpus cell eventually take over the corpus. Here is the first chimeric set of data to support the hypothesis of a one-celled meristem in eudicots rather than the traditional view of a muticellular meristem.

The Arabidopsis thaliana MERISTEM LAYER 1 promoter specifies epidermal expression in meristems and young primordia

The Arabidopsis thaliana MERISTEM LAYER 1 (ATML1) gene is expressed in the epidermis of developing embryos and shoot meristems. To identify regulatory sequences necessary for epidermis-specific expression, three fusions of overlapping ATML1 genomic sequences to the GUS reporter gene were introduced into Arabidopsis plants. All fusion genes conferred epidermis-specific expression of both GUS mRNA and protein activity but varied in both the timing and relative levels of expression, suggesting partial redundancy of ATML1 regulatory elements. This study defines L1-specific regulatory sequences that are sufficient to direct foreign gene expression in a layer-specific manner.

GENETICS OF ANGIOSPERM SHOOT APICAL MERISTEM DEVELOPMENT

▪ Abstract  Recent progress has been made in the genetic dissection of angiosperm shoot apical meristem (SAM) structure and function. Genes required for proper SAM development have been identified in a variety of species through the isolation of mutants. In addition, genes with expression patterns indicating they play a role in SAM function have been identified molecularly. The processes of SAM formation, self-renewal, and pattern formation within the SAM are examined with an emphasis on the contributions of recent classical and molecular genetic experiments to our understanding of this basic problem in plant developmental biology.

Acquisition of identity in the developing leaf

Leaves are produced repeatedly from the shoot apical meristem of plants. Molecular and cellular evidence show that identity of the leaf and its parts is acquired progressively and that the underlying process changes as the leaf matures. The relative importance of cell lineage compared with a position-dependent model for specifying cell fates is discussed.