Thursday 7 September 2017
Perturbing phosphoinositide homeostasis during vascular cell differentiation: a tale of two halves?
The plant vascular network is an inter-organ communication system that enables plants to respond and adapt to environmental and developmental stimuli. While xylem is required for the transport of water and nutrients by the root to the above-ground organs, phloem delivers photosynthetic compounds as well as essential growth regulators through the whole plant body. To become functional units, phloem and xylem cells undergo two different morphogenetic developmental programs which involve the reinforcement of their cell wall and total or partial cell clearance. As a final stage of cell differentiation, xylem elements undergo vacuolar-driven programmed cell death (PCD) resulting in a system of adjoining hollow cells. By contrast, mature protophloem cells undergo a rather complex and poorly understood differentiation program which involves cell enucleation and vacuolar degradation. Interestingly, our results show that a genetic disturbance of the phosphoinositide homeostasis at the plasma membrane (PM) antagonistically impinge on both vascular programs. In particular, an increase of phosphatidylinositol 4,5-bis-phosphate [PtdIns(4,5)P2 ] rewires intracellular trafficking towards the vacuole in Arabidopsis root cells. Consequently, an enhanced phosphoinositide-mediated vacuolar biogenesis leads to premature PCD and secondary cell wall building in xylem cells. Inhibition of vesicular trafficking from trans-Golgi network (TGN) to the vacuole by brefeldin A (BFA) application abolishes the premature xylem differentiation triggered by increasing PtdIns(4,5)P2 levels. On the contrary, BFA treatments induces the abnormal formation of big vacuoles in mature protophloem cells, preventing cell clearance and thus, tissue functionality. Moreover, a fine-tuned cycling of the inositol 5’ phosphatase COTYLEDON VASCULAR PATTERN 2 from TGN to the PM is required to tightly regulate PtdIns(4,5)P2 turnover in protophloem cells to regulate vascular differentiation rate. Together, our data indicate that a tight PM phosphoinositide homeostasis is required to modulate vacuolar biogenesis, contributing to antagonistically regulate vascular cell differentiation.
Contact : Benjamin Péret