The Effect of a Genetically Reduced Plasma Membrane Protonmotive Force on Vegetative Growth of Arabidopsis      

Abstract

The plasma membrane proton gradient is an essential feature of plant cells. In Arabidopsis (Arabidopsis thaliana), this gradient is generated by the plasma membrane proton pump encoded by a family of 11 genes (abbreviated as AHA, for Arabidopsis H + -ATPase), of which AHA1 and AHA2 are the two most predominantly expressed in seedlings and adult plants. Although double knockdown mutant plants containing T-DNA insertions in both genes are embryonic lethal, under ideal laboratory growth conditions, single knockdown mutant plants with a 50% reduction in proton pump concentration complete their life cycle without any observable growth alteration. However, when grown under conditions that induce stress on the plasma membrane protonmotive force (PMF), such as high external potassium to reduce the electrical gradient or high external pH to reduce the proton chemical gradient, aha2 mutant plants show a growth retardation compared with wild-type plants. In this report, we describe the results of studies that examine in greater detail AHA2's specific role in maintaining the PMF during seedling growth. By comparing the wild type and aha2 mutants, we have measured the effects of a reduced PMF on root and hypocotyl growth, ATP-induced skewed root growth, and rapid cytoplasmic calcium spiking. In addition, genome-wide gene expression profiling revealed the up-regulation of potassium transporters in aha2 mutants, indicating, as predicted, a close link between the PMF and potassium uptake at the plasma membrane. Overall, this characterization of aha2 mutants provides an experimental and theoretical framework for investigating growth and signaling processes that are mediated by PMF-coupled energetics at the cell membrane.

Phosphoproteomic Analyses Reveal Early Signaling Events in the Osmotic Stress Response

“…This pattern of phosphoregulation is distinct from the AHA response to KCl treatment, suggesting that these different forms of osmotic stress have unique effects on AHA activity. This observation is supported by genetic data showing that aha2 null mutants are hypersensitive to KCl but not sorbitol or NaCl treatment (Haruta and Sussman, 2012).…”

Analysis of the Root System Architecture of Arabidopsis Provides a Quantitative Readout of Crosstalk between Nutritional Signals

“…pH is a good candidate; K-influx promotes H + -efflux through the proton pump (Amtmann et al, 1999), while nitrate influx is accompanied by H + -influx (Miller et al, 2007). The importance of apoplastic pH for extension growth and cell wall deposition is well documented, and its potential effect on MR angle is further supported by a report that root skewing is ATP dependent and reduced in aha2 mutants, defective in the major root H + -ATPase (Haruta and Sussman, 2012).…”

The Tomato 14-3-3 Protein TFT4 Modulates H+ Efflux, Basipetal Auxin Transport, and the PKS5-J3 Pathway in the Root Growth Response to Alkaline Stress

“…Optimal primary root elongation requires the fine regulation of H + -ATPase-mediated H + efflux, particularly at the root tip (Staal et al, 2011;Haruta and Sussman, 2012). Under alkaline stress, in Arabidopsis (Arabidopsis thaliana), PROTEIN KINASE5 (PKS5) and the chaperone DNAJ HOMOLOG3 (J3) play important roles in H + efflux by regulating the interaction between PM H + -ATPase and 14-3-3 proteins (Fuglsang et al, 2007;Yang et al, 2010).…”