Perturbing phosphoinositide homeostasis oppositely affects vascular differentiation in Arabidopsis thaliana roots

Abstract

The plant vascular network consists of specialized phloem and xylem elements that undergo two distinct morphogenetic developmental programs to become transport-functional units. Whereas vacuolar rupture is a determinant step in protoxylem differentiation, protophloem elements never form a big central vacuole. Here, we show that a genetic disturbance of phosphatidylinositol 4,5-bis-phosphate [PtdIns(4,5)P2] homeostasis rewires cell trafficking towards the vacuole in Arabidopsis thaliana roots. Consequently, an enhanced phosphoinositide-mediated vacuolar biogenesis correlates with premature programmed cell death (PCD) and secondary cell wall elaboration in xylem cells. By contrast, vacuolar fusion events in protophloem cells trigger the abnormal formation of big vacuoles, preventing cell clearance and tissue functionality. Removal of the inositol 5′ phosphatase COTYLEDON VASCULAR PATTERN 2 from the plasma membrane (PM) by brefeldin A (BFA) treatment increases PtdIns(4,5)P2 content at the PM and disrupts protophloem continuity. Conversely, BFA application abolishes vacuolar fusion events in xylem tissue without preventing PCD, suggesting the existence of additional PtdIns(4,5)P2-dependent cell death mechanisms. Overall, our data indicate that tight PM phosphoinositide homeostasis is required to modulate intracellular trafficking contributing to oppositely regulate vascular differentiation.

A Reservoir of Pluripotent Phloem Cells Safeguards the Linear Developmental Trajectory of Protophloem Sieve Elements

“…Because RPK2 can interact with BAM1 to regulate cell proliferation within the root meristem [29], it appears possible that the root may establish a gradient of CLE45 signaling by modulating the dynamics of its receptors. To this end, previous studies have shown the role of CVP2 and CVL1 in modulating vesicle trafficking in protophloem cells [12]. An enrichment of the CVP2-and CVL1-enzymatic product PtdIns(4,5)P 2 at the plasma membrane redirects vesicle trafficking toward the vacuole [12] and may potentially displace plasma-membrane-localized receptors essential for proper CLE peptide signaling.…”

“…As a widely used drug to alter vesicle trafficking, BFA inhibits ADP-ribosylation factor-guanine-exchange factors [25]. Previous studies have reported the ability of this compound to generate gap cells in the protophloem strand within 24-48 h treatments [12,26], although the underlying mechanisms remain unknown. Remarkably, BFA-triggered gap cells also exhibit SAPL and NaKR1 expression (Figures S1F and S1I), mimicking the cvp2 cvl1 phenotype.…”

Plastidial NAD-Dependent Malate Dehydrogenase: A Moonlighting Protein Involved in Early Chloroplast Development through Its Interaction with an FtsH12-FtsHi Protease Complex

“…To generate artificial microRNA silencing constructs, we recombined the amiRNA miR-mdh-1 cassette in pDONR221 (described previously; Beeler et al, 2014) into a vector containing an estradiol-inducible cassette (XVE) driven by the UBIQUITIN10 promoter, via the LR Clonase reaction (Lee et al, 2013;Gujas et al, 2017). Two artificial microRNA silencing cassettes for FtsH12 were designed and cloned using the Web MicroRNA Designer tool (WMD3, wmd3.weigelworld.org; Ossowski et al, 2008) according to the provided instructions.…”

Meeting report – Cellular gateways: expanding the role of endocytosis in plant development

“…Her lab is interested in the differentiation process of the xylem and phloem elements in the vascular network. By genetically affecting the balance between phosphatases and kinases that are involved in the biogenesis of PI(4,5)P 2 , her group found that high levels of PI(4,5)P 2 stimulate intracellular trafficking towards the vacuole, and this effect promotes protoxylem differentiation, but prevents protophloem differentiation (Gujas et al, 2017).…”