The vascular network provides plants with structural support and long-distance transport, meaning that vascular tissues must predictably differentiate to form continuous strands. To uncover the mechanisms that establish and maintain the vascular pattern, we take advantage of the Arabidopsis root tip, which has a stereotypical arrangement with procambial cells separating opposite phloem poles from a central xylem axis. We are also using Populus spp. and Betula spp. as model organisms to study plant development in species with pronounced secondary growth.
Employing a tree species as a model organism in genetic studies pose a challenge in contrast to annual plants such as Arabidopsis thaliana. This is due to several years long juvenile stage which trees usually require before they start to flower and subsequently enable crossings. Conveniently, Betula spp. can be induced to flower within a year when introduced into special accelerated flowering conditions. We utilize accelerated flowering and forward genetics approach to study developmental mechanisms underlying distinct Betula spp. phenotypes. We also employ translational approach to study various overexpression lines for enhanced biomass production in Populus spp.
Research in our lab and elsewhere has uncovered a central role for the phytohormones auxin and cytokinin in vascular patterning. Cytokinin acts to promote procambial proliferation at the expense of xylem, while auxin signalling is critical for the specification of the xylem tissues. Multiple feedback loops between the two hormones at the level of synthesis, metabolism, and signalling determine the size and arrangement of the vascular cylinder. We use genetic screens in sensitized backgrounds to identify novel components of these networks, as well as other genetic factors regulating vascular development. In addition, we use microarrays and whole-transcriptome sequencing to investigate the interactions that define the networks and the changes that occur during the course of development.
Communication between cells has also emerged as an important factor in vascular development. Plasmodesmata bridge cell walls to connect the cytoplasm of neighbouring plant cells, transforming them into a continuous, though compartmentalized, space called the symplast. Phloem is rich in plasmodesmata-like structures.
Using a genetic screen, we discovered a mutation in a callose synthase gene which led to excess callose deposition at plasmodesmata, disrupting intercellular connectivity and resulting in defects in vascular patterning. By expressing the mutated gene under various inducible promoters, we can selectively block plasmodesmatal connections at a chosen time and in specific tissues. This enables us to probe the role of the connections between particular tissue regions at different stages of development. We will use this technology to identify proteins that move across these channels and clarify their role in vascular development, as well as mapping the symplastic connections in the Arabidopsis root tip. We will also focus on phloem morphogenesis.