An emerging concept in plant developmental biology is that the genetic control of patterned cell division is the key to understanding plant development. Plants depend on controlled cell divisions in order to make new organs throughout their life cycle. Organ development in flowering plants results almost entirely from the patterned control of the number, place and plane of cell division, in conjunction with regulated and coordinated cellular expansion. The establishment of patterned control occurs during several major phases of plant development, namely during embryogenesis, shoot and root development, and during inflorescence and floral morphogenesis. A novel homeobox gene, ATML1, in Arabidopsis thaliana is expressed very early in plant development, being first detected in the zygote, then segregated to the apical cell and later to the early protoderm during asymmetric cell division. An atml1 mutant exhibits an embryo-defective phenotype, with a loss of cellular patterning. Based on its pattern of expression and its mutant phenotype, the ATML1 gene and its protein product are likely to play a critical role in early embryogenesis, specifically contributing to the control of pattern formation during embryogenesis and possibly later during shoot development. This project seeks to determine the function of ATML1 in embryogenesis and SAM organization/function by characterizing the genetics and phenotype of an atml1 mutant. The specific objectives are to use a combination of classical and molecular genetic approaches to study the effect of the T-DNA insertion in the atml1 mutant line. This research will provide critical information for our understanding of the basis of cell division and early pattern formation during embryogenesis, and the specification of the identity of an L1 cell layer in the SAM. Localization of the ATML1 gene products should also provide insight into current hypotheses concerning protein trafficking and lineage versus positional information in the determination of pattern in plants.
