On the origin of vascular species

Vascular tissues are indispensable in higher plants, where they provide physical support and are responsible for long-range solute transport. Thus, many agronomic traits depend on the ability of cells to acquire vascular identity. For example, new vascular connections must be established during grafting, which is a common strategy to enhance yield or to acquire disease resistance in crops. Despite the importance of vascular identity, little is known on how it is established. To date, vascular development has been intensively studied in root, stem and leaf. However, given tissue complexity, it is challenging to identify early developmental switches.

The processes that lead to the formation of the mature vascular bundle encompasses four discrete processes. Cells first need to (1) acquire vascular identity, then (2) divide to create a bundle, (3) become patterned into xylem, phloem and cambium cell types and finally (4) terminally differentiate to functional transport tissue (Figure 1). In the past few decades research has focused on the latter 3 aspects of vascular development.

Figure 1: Vascular tissue development encompasses identity specification (A,B), growth, patterning (C,D), and differentiation (D). These processes are temporally isolated in the embryo (A-C), while they occur simultaneously in post-embryonic organs (e.g. conifer stem in D). Adapted from Scarpella and Helariutta (2010) and Biodisc ART.com.
Figure 1: Vascular tissue development encompasses identity specification (A,B), growth, patterning (C,D), and differentiation (D). These processes are temporally isolated in the embryo (A-C), while they occur simultaneously in post-embryonic organs (e.g. conifer stem in D). Adapted from Scarpella and Helariutta (2010) and Biodisc ART.com.
In this project, I will use the simple and predictable Arabidopsis embryo to study the earliest specification of vascular identity in the absence of subsequent vascular growth, patterning and differentiation. I will combine complementary approaches to identify the elusive regulators of vascular identity. While some approaches start from the known involvement of the hormone auxin and its transcriptional mediator MONOPTEROS, others will yield candidate regulated from relatively unbiased approaches (Yeast One Hybrid, EMS, activation tagging). These approaches will yield several candidate regulators of vascular identity.

Candidate regulators will then be validated via a series of experiments. I will look at their expression patterns in embryo and root, their role in vascular tissue development and their ability to trigger vascular identity ectopically. We expect this project to yield “master” regulators that control and can induce vascular identity. These should serve as molecular markers for the competence to de novo vascular tissue formation, and as leads for engineering vascular development in crops.