Plant Cell Growth and Ion Flux Responses to the Streptomycete Phytotoxin Thaxtomin A: Calcium and Hydrogen Flux Patterns Revealed by the Non-invasive MIFE Technique

Abstract

Thaxtomin A, a key phytotoxin produced by plant pathogenic Streptomyces sp., is implicit in common scab disease expression in potato. Primary targets and modes of action of thaxtomin A toxicity in plant cells are not well understood. In this work, early signalling events associated with thaxtomin A toxicity were studied using the ion-selective microelectrode ion flux estimation (MIFE) technique. Thaxtomin A-induced changes in net ion fluxes were measured across the plasma membrane (PM) of root and pollen tube tissue in Arabidopsis thaliana and tomato. Within a minute after toxin application, a rapid and short-lived Ca2+ influx was observed. Well ahead of the marked inhibition of root growth, a significant shift towards net H+ efflux across the PM occurred in all tissues. Similar to root tissues, thaxtomin A significantly modified ion flux profiles from growing pollen tubes. Thaxtomin A was more effective in young, physiologically active tissues (root elongation zone or pollen tube apex), suggesting a higher density of thaxtomin A-binding sites in these regions. Overall, our data provide the first evidence that thaxtomin A triggers an early signalling cascade, which may be crucial in plant-pathogen interactions. It also suggests a possible interaction between thaxtomin A and PM auxin receptors, as revealed from experiments on the auxin-sensitive ucu2-2/gi2 A. thaliana mutant.

Leaf Senescence Signaling: The Ca2+-Conducting Arabidopsis Cyclic Nucleotide Gated Channel2 Acts through Nitric Oxide to Repress Senescence Programming

“…Results in Figure 2, B and C, indicate that with regard to the rapid senescence that occurs in detached leaves kept in the dark, application of Gd 3+ , a channel blocker that prevents inward currents through plasma membrane Ca 2+ -conducting channels (Tegg et al, 2005), mimics the phenotype shown by dnd1. Further studies were undertaken to determine if the effect of Gd 3+ on senescence programming could be observed at the biochemical and gene expression level.…”

Auxin-Induced Resistance to Common Scab Disease of Potato Linked to Inhibition of Thaxtomin A Toxicity

“…Auxin effects on the morphological development of len-ticels or periderm during early tuber growth, a period of susceptibility to infection by S. scabiei (2,4), might help explain how auxin treatments confer protection against common scab disease. Furthermore, recent evidence from our laboratory suggests an interaction whereby increased sensitivity to auxin correlates with an increased sensitivity to thaxtomin A (37).…”

Ca 2 + signaling by plant Arabidopsis thaliana Pep peptides depends on AtPepR1, a receptor with guanylyl cyclase activity, and cGMP-activated Ca 2+ channels

“…4A). Promotion of cytosolic Ca 2+ spikes in roots of Arabidopsis seedlings by application of several different ligands has been shown to inhibit primary root growth (26,32). In addition, we have found that some members of the CNGC protein family are expressed in roots, contribute to Ca 2+ uptake, and facilitate Ca 2+ -mediated inhibition of root elongation under some conditions (33).…”

“…S6A. Lanthanides such as Gd 3+ and La 3+ block plant plasma membrane Ca 2+ channels (26). Gd 3+ has been specifically shown to block inwardly rectified cyclic nucleotide-activated Ca 2+ channels in the plasma membrane of Arabidopsis leaf cells (20).…”