Abstract
Auxin controls a myriad of plant developmental processes and plant response to environmental conditions. Precise trafficking of auxin transporters is essential for auxin homeostasis in plants. Here, we report characterization of Arabidopsis CTL1, which controls seedling growth and apical hook development by regulating intracellular trafficking of PIN-type auxin transporters. The CTL1 gene encodes a choline transporter-like protein with an expression pattern highly correlated with auxin distribution and is enriched in shoot and root apical meristems, lateral root primordia, the vascular system, and the concave side of the apical hook. The choline transporter-like 1 (CTL1) protein is localized to the trans-Golgi network (TGN), prevacuolar compartment (PVC), and plasma membrane (PM). Disruption of CTL1 gene expression alters the trafficking of 2 auxin efflux transporters—Arabidopsis PM-located auxin efflux transporter PIN-formed 1 (PIN1) and Arabidopsis PM-located auxin efflux transporter PIN-formed 3 (PIN3)—to the PM, thereby affecting auxin distribution and plant growth and development. We further found that phospholipids, sphingolipids, and other membrane lipids were significantly altered in the ctl1 mutant, linking CTL1 function to lipid homeostasis. We propose that CTL1 regulates protein sorting from the TGN to the PM through its function in lipid homeostasis.
Highlights
Dynamic endomembrane trafficking delivers proteins and other cargo molecules to a variety of organelles and controls almost all aspects of plant development and physiology, including gravitropism, epidermis differentiation, guard cell movement, cell wall remodeling, defense against pathogens, and hormone signaling [1]
In tracking down the mechanism of choline transporter-like 1 (CTL1) function, we discovered that CTL1 is closely associated with auxin signaling in the control of plant developmental processes
We took a comprehensive reverse genetic approach to identify the function of these proteins by screening Arabidopsis SALK transfer deoxyribonucleic acid (T-DNA) insertion lines disrupting the expression of corresponding genes
Summary
Dynamic endomembrane trafficking delivers proteins and other cargo molecules to a variety of organelles and controls almost all aspects of plant development and physiology, including gravitropism, epidermis differentiation, guard cell movement, cell wall remodeling, defense against pathogens, and hormone signaling [1]. In this context, exocytosis and endocytosis determine the abundance and dynamics of signaling receptors and transporters at the plasma membrane (PM), which in turn afford cells the ability to respond to extracellular stimuli. Many components have been shown to affect the trafficking and PM abundance of auxin transporters. The mutations in genes encoding these transporters are often trackable because the mutants often show severe phenotypic changes in plant growth and development
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