Phospholipase Dζ2 Drives Vesicular Secretion of Auxin for Its Polar Cell-Cell Transport in the Transition Zone of the Root Apex

Abstract

Auxin (IAA) is versatile signalling molecule of plants, currently classified as plant hormone. But there are data suggesting that auxin is acting also as plant-specific morphogen, electric-responses inducing transmitter, and as general signalling molecule used for plant-bacteria communication. Our previous data revealed that auxin is associated with secretory endosomes and also highly enriched within cell walls of cells active in transcellular auxin transport. Our present data, based on in vivo non-invasive auxin flux recordings, reveal that auxin is secreted out of synaptic-like domains specialized for efflux of auxin in root apex cells highly active in polar cell-cell transport of auxin. We obtained both genetic and pharmacological evidence that phospholipase Dzeta2 drives vesicular secretion of auxin for its polar transcellular transport in the transition zone of the root apex. Secretion of auxin via secretory vesicles has far-reaching consequences not only for our understanding of cell-cell auxin transport but also for plant sciences as a whole.

The Signal Transducer NPH3 Integrates the Phototropin1 Photosensor with PIN2-Based Polar Auxin Transport in Arabidopsis Root Phototropism

“…To determine the possible mechanism for the altered phototropic responses of the pin2, nph3, phot1, and phot1phot2 mutants, we further measured auxin flux profiles in vivo in the root apical region using a noninvasive microelectrode system (Mancuso et al, , 2007McLamore et al, 2010), which indicated that all lines have a net rhizosphere auxin influx in the root tip region (Figures 2A and 2B Two-way ANOVAs were performed to compare significant differences between measured peak values of auxin flux rates. Light conditions and different mutant lines were the two sources of variation; both caused extremely significant differences (P < 0.001).…”

Longitudinal zonation pattern inArabidopsisroot tip defined by a multiple structural change algorithm

“…Thus, for a particular cell file within the arabidopsis root, the TD can also be defined as the region where cells endoreduplicate and continue elongating at the same rate as in the PD. It has also been shown that phospholipase Df2, involved in vesicle trafficking, is strongly expressed in the transition zone (Li and Xue, 2007;Mancuso et al, 2007). The MSC analysis used here clearly shows that before the onset of rapid elongation all cells within a file, irrespective of the tissue type, are distributed in two subsets separated by an identifiable transition: those in the PD and those in the TD.…”

Plant neurobiology

“…12 The most active electric activity has been reported in the root apex zone 13 which shows also the most active polar auxin transport from cell-to-cell in vivo. 14,15 This so-called transition zone 16 shows numerous characteristics which indicate that it might act as a plant-specific, 'brain-like' command centre 17 which integrates and possibly memorizes numerous sensory experiences. 17,18 Because this specific root-apical zone initiates root tropisms, 17,18 it can be speculated that it also integrates the motor-like activity of growing root apices by which roots navigate through their complex environment.…”