In this issue of Development, two papers exploit the genetic tractability of the model plant Arabidopsis thaliana to investigate plant vascular development, and by doing so shed new light on processes that are of general importance to multicellular life. In the first study (see ), Naramoto et al. investigate the role of VAN3 in the formation of a continuous leaf vasculature and report that both its subcellular localisation and activity are regulated by phosphoinositide (PI) signalling. VAN3 is an ARF GTPase-activating (ARF-GAP) protein, a family of proteins that regulate multiple cellular processes, including endocytosis and secretion, through their roles in vesicle transport and protein trafficking. Consistent with it functioning in the post-Golgi transport pathway, VAN3, the authors report,localises to subdomains of the trans-Golgi network (TGN). Through genetic interaction studies and yeast two-hybrid screening, they identify two novel regulators of VAN3 localisation: CVP2, an inositol polyphosphate 5′phosphatase, and VAN3-binding protein (VAB). CVP2, they show, regulates VAN3 localisation to the TGN by regulating cellular PI levels, whereas VAB helps to recruit VAN3 to PI-enriched TGN subdomains. PIs also control the ARF-GAP activity of VAN3, leading the researchers to propose that they have a dual role in regulating the subcellular distribution and enzymatic activity of VAN3. Future work should identify whether VAN3 is also involved in polar auxin transport.
In the second study, Pascal Genschik and colleagues turned to Arabidopsis development to shed light on the activity of the ubiquitin protein ligase APC/C(), which is important for DNA replication and cell division but which surprisingly remains active in post-mitotic vertebrate cells, such as neurons. The researchers report that APC/C also remains active in most post-mitotic Arabidopsis cells, and that reduced APC/C activity in mutant plants results in developmental defects. These defects include disturbed vein patterning in the cotyledon (the first leaf of a germinating seed) and increased vascular tissue, indicating that APC/C functions in vascular development and organisation. Although the role of PIs in vesicular trafficking and the post-mitotic functions of APC/C now await further investigation, these two studies illustrate the power of diverse model systems for biological research.
