Plant vascular development: from early specification to differentiation.

Vascular tissues in plants are crucial to provide physical support and to transport water, sugars and hormones and other small signalling molecules throughout the plant. Recent genetic and molecular studies have identified interconnections among some of the major signalling networks that regulate plant vascular development. Using Arabidopsis thaliana as a model system, these studies enable the description of vascular development from the earliest tissue specification events during embryogenesis to the differentiation of phloem and xylem tissues. Moreover, we propose a model for how oriented cell divisions give rise to a three-dimensional vascular bundle within the root meristem

Auxin regulation of embryo development

Important steps in plant development are made shortly after fertilization. In a brief succession of cell divisions, the zygote is transformed into an embryo, a multicellular structure carrying all fundamental tissue types and the meristems. Hence, embryogenesis offers excellent opportunities to dissect the molecular control and cellular mechanisms underlying plant development. In the past decades, forward and reverse genetics studies have revealed that the plant hormone auxin plays a central role in the establishment of pattern and polarity in the Arabidopsis embryo. Here, we review the roles that localized auxin biosynthesis, directional transport and cell type-specific response play in embryo development. We focus on the molecular mechanisms, as well as the feedbacks that connect these disparate levels of regulation. Finally, we discuss the potential for hormonal cross-talk in auxin-dependent control of the key events during the earliest, formative phase of plant life.</p