Insights into the regulation of plant plasma membrane H+-ATPase: Interactions with microbial compounds and implications for root hair growth

Publikation: Bog/antologi/afhandling/rapportPh.d.-afhandlingForskning

Abstract

The plant plasma membrane (PM) H+-ATPase is a P-type ATPase that catalyzes the transport of protons from the cytoplasm into the apoplast at the expense of ATP. This generates a steep electrochemical proton gradient, creating the membrane potential needed for secondary transport and nutrient uptake from the soil surrounding the plant. The activity of the PM H+ATPase is upregulated during cell expansion by protein kinase activity perceived at the Cterminal regulatory domain. Activation of the proton pump leads to apoplastic acidification that activates cell wall loosening enzymes, cleavage of cell wall cross-linkages, allowing rapid cell expansion. The PM H+-ATPase is integral to plant growth and development, which makes it a key target enzyme for microorganisms during plant-microbe interactions.

This thesis describes the molecular interaction between natural compounds from microorganisms that regulate the activity of the PM H+-ATPase. Most natural compounds from microorganisms found in literature interact with the PM H+-ATPase through indirect regulation by modifications to the surrounding lipid bilayer. This thesis focuses on the non-host specific fungal toxin tenuazonic acid (TeA) and its inhibitory mechanism of the PM H+-ATPase. TeA is a potent phytotoxin with herbicidal activity towards the model plant Arabidopsis thaliana. TeA inhibits root elongation and causes cell death at low concentrations when applied. The herbicidal activity of TeA was found to be an effect of PM H+-ATPase inhibition, where TeA binds to the Regulatory Region I of the C-terminal domain of the pump, thus stabilizing the pump in an autoinhibited state and preventing pump activation. This supports the notion for the use of TeA as a potential herbicide. Investigations of PM H+-ATPase stimulated activity by Trichoderma harzianum peptaibols showed that this stimulated effect was caused by modifications of the lipid bilayer. Thus, making the H+-ATPase an indirect target of peptaibol activity, during growth stimulated interactions between T. harzianum and plants.

Regulation of root hair growth is important for increased root surface area and nutrient uptake from the soil. In Arabidopsis there are two major PM H+-ATPase (AHA) isoforms involved the in regulation of root hair growth, AHA2 and AHA7, both of which are located throughout the plasma membrane of growing root hairs, exhibiting lateral diffusion within the membrane. Both AHA2 and AHA7 are important for sustaining the membrane potential across the plasma membrane in growing root hairs, while AHA2 is important for the regulation of root hair growth in response to external pH changes. Furthermore, is AHA2 activity regulated by root hair-specific the receptor-like kinase ERULUS, during root hair growth.

This thesis describes two projects with the PM H+-ATPase in the center, showing that the regulation of PM H+-ATPase activity is important for plant-microbe interactions and root hair growth.

Citationsformater