Control of Arabidopsis thaliana embryogenesis and the developmental regulation of embryo identity at the transcriptional level

Plant embryogenesis is a highly regulated developmental period resulting in a fully functional, metabolically paused desiccated seed. Embryo development can occur in multiple forms, such as zygotic, somatic, microspore and apomictic embryogenesis. There are transcriptional regulators that are active in many forms of embryogenesis, suggesting common genetic regulation. One such transcriptional regulator is LEAFY COTYLEDON1 (LEC1). Expression of LEC1 is limited to developing somatic and zygotic embryos. LEC1 expression during vegetative development causes a developmental switch inducing embryo development. lec1 mutant seeds lose embryo identity resulting in embryos with mixed vegetative and embryonic traits. In this thesis I have used the LEC1 gene as a tool to understand the regulation of embryogenesis.; The LEC1 protein is one member of a large family in Arabidopsis . I analyzed the family member with the closest sequence identity to LEC1, LEC1-LIKE (L1L). L1L is expressed during embryogenesis; loss of L1L function leads to embryo arrest, and analysis of transgenic plants expressing L1L during vegetative growth show L1L can induce embryonic characteristics. Thus the sequence identity existing between LEC1 and L1L allowed for the discovery of the LEC1-type plant family members.; To analyze the function of LEC1 during embryogenesis and vegetative development, I created transgenic plants with modified LEC1 activities. LEC1 was shown to regulate desiccation tolerance during seed maturation independent of activity during morphogenesis. Activation of LEC1 in vegetative and floral development resulted in the production of cotyledon-like structures. LEC1 has the ability to cause a conversion to embryonic developmental programming.; LEC1 transcriptional regulation of gene expression was monitored by Genechip analysis. During embryogenesis and the vegetative development stage LEC1 regulated different genes unique to each stage and also genes shared in both stages. Changes in vegetative gene expression accompanying LEC1 activity suggest a possible link between embryogenesis and stress tolerance. Results of my analysis of the LEC1 protein and LEC1 activity suggest broad transcriptional changes result in embryogenic developmental programming during plant development.