Vacuolar transporters and their essential role in plant metabolism

Abstract

Following the unequivocal demonstration that plants contain at least two types of vacuoles, scientists studying this organelle have realized that the plant 'vacuome' is far more complex than they expected. Some fully developed cells contain at least two large vacuoles, with different functions. Remarkably, even a single vacuole may be subdivided and fulfil several functions, which are supported in part by the vacuolar membrane transport systems. Recent studies, including proteomic analyses for several plant species, have revealed the tonoplast transporters and their involvement in the nitrogen storage, salinity tolerance, heavy metal homeostasis, calcium signalling, guard cell movements, and the cellular pH homeostasis. It is clear that vacuolar transporters are an integrated part of a complex cellular network that enables a plant to react properly to changing environmental conditions, to save nutrients and energy in times of plenty, and to maintain optimal metabolic conditions in the cytosol. An overview is given of the main features of the transporters present in the tonoplast of plant cells in terms of their function, regulation, and relationships with the microheterogeneity of the vacuome.

Nitrate Reductase Knockout Uncouples Nitrate Transport from Nitrate Assimilation and Drives Repartitioning of Carbon Flux in a Model Pennate Diatom

“…In yeast, and in Arabidopsis, regions within the vacuolar bilayer, enriched in sphingolipids and sterols (Chung et al, 2003;Finnigan et al, 2011), have been identified as essential to the function of vacuolar-ATPases (Ozolina et al, 2013;Yoshida et al, 2013). Vacuolar-ATPases are the proton pumps in plants (reviewed in Martinoia et al, 2007) that provide energy for NO 3 2 transport into the vacuole via NO 3 2 ClC transporters identified in this study. The presence of putative NO 3 2 vacuolar transporters in P. tricornutum, combined with results supporting the likelihood that diatom vacuolar membrane lipids can be constructed from recycled thylakoid membrane lipids, prompts consideration of whether marine NO 3 2 upwelling events produce a similar response in P. tricornutum and other vacuolate diatoms.…”

“…A comparison of wild-type expression profiles for two vacuolar transporter genes, EG01952 and J28245, clearly documents alternatively timed responses to NO 3 2 availability ( Figure 8C). In addition to NO 3 2 (ClC) vacuolar transporters, V-type ATPases and H + PPases provide energy, or generate a proton motive force, to pump NO 3 2 and other ions across the vacuolar membrane (reviewed in Martinoia et al, 2007). Their expression profiles were similar to the NO 3 2 (ClC) vacuolar transporter profiles in both the wild-type and NR-KO14 transcriptomes (Supplemental Data Set 1).…”

Arabidopsis V-ATPase activity at the tonoplast is required for efficient nutrient storage but not for sodium accumulation

“…All vacuolar functions require massive fluxes of ions and metabolites that are channeled by a battery of vacuolar transport proteins, many of which have been well characterized physiologically, but the nature of several transporters remains to be identified (1). Among those characterized on the molecular level are, e.g., those transporting NO 3 − , Na + , and protons.…”

Impaired Function of the Tonoplast-Localized Sucrose Transporter in Rice, OsSUT2, Limits the Transport of Vacuolar Reserve Sucrose and Affects Plant Growth

“…Considering that Suc is temporarily stored in the vacuoles of photosynthetic assimilatory tissues (Riens et al, 1991;Winter et al, 1993;Martinoia et al, 2007;Neuhaus, 2007;Linka and Weber, 2010), this raises the question of the involvement and function of tonoplast-localized SUTs in plant growth and development in cereals. The rice genome contains five SUTs, OsSUT1 to OsSUT5 (Aoki et al, 2003).…”