Auxins and Cytokinins—The Role of Subcellular Organization on Homeostasis

Abstract

Plant hormones are master regulators of plant growth and development. Better knowledge of their spatial signaling and homeostasis (transport and metabolism) on the lowest structural levels (cellular and subcellular) is therefore crucial to a better understanding of developmental processes in plants. Recent progress in phytohormone analysis at the cellular and subcellular levels has greatly improved the effectiveness of isolation protocols and the sensitivity of analytical methods. This review is mainly focused on homeostasis of two plant hormone groups, auxins and cytokinins. It will summarize and discuss their tissue- and cell-type specific distributions at the cellular and subcellular levels.

Plant Hormones in Phytoplasma Infected Plants

“…Several of these changes are related to genes associated with the expression of hormones. Plant hormones are naturally occurring, small, organic molecules that have important regulatory roles in plant growth and developmental processes (Rijavec and Dermastia, 2010; Wasternack and Song, 2016; Liu et al, 2017; Ahanger et al, 2018; Binenbaum et al, 2018; Camara et al, 2018; Ma et al, 2018; Skalický et al, 2018; Weijers et al, 2018; Wasternack and Strnad, 2019). They are also involved in plant defense responses against pathogens (Pieterse et al, 2012; Shigenaga and Argueso, 2016; Shigenaga et al, 2017).…”

The Lateral Root Cap Acts as an Auxin Sink that Controls Meristem Size

“…PIN5 is localized at the endoplasmic reticulum (ER) and mediates auxin flow from the cytoplasm to the ER lumen [26]. Either the ER or the cytosol have been hypothesized as compartments of activity of GH3 auxin conjugases, but supporting evidence for one or the other location is still lacking [27][28][29].…”

Transporter-Mediated Subcellular Distribution in the Metabolism and Signaling of Jasmonates

“…Information on the intracellular transport of JAs is limited, due to technical difficulties in measuring JAs in different subcellular compartments (Skalicky et al, 2018). The significance of subcellular distribution on the metabolism and signaling of JAs has been revealed by the identification of peroxisomal ATP-binding cassette (ABC) COMATOSE (CTS) transporter.…”

“…However, dual localizations at the ER and PM of the short PIN (PIN-FORMED) permease-like auxin transporters, which lack the extensive hydrophilic loop separating two transmembrane domains, have also been revealed in Arabidopsis epidermal and root hair cells, as well as in tobacco BY-2 cells. These ER-localized PINs presumably regulate auxin homeostasis by pumping auxin into (PIN5) or out (PIN8) of the ER lumen or hypothetically from the ER lumen into the nucleus (PIN6 and PIN8) (Mravec et al, 2009; Bender et al, 2013; Viaene et al, 2013; Park et al, 2017; Skalicky et al, 2018). The identification of AtJAT1 further supports a common theme that the transporter-modulated subcellular partition plays an essential role in modulating the signaling of plant hormones.…”