Two Plasma Membrane H+-ATPase Genes Expressed in Guard Cells of Vicia faba Are Also Expressed Throughout the Plant

Abstract

Guard cells modulate stomatal apertures in response to hormones, metabolic demands and environmental stimuli. The guard cell PM H(+)-ATPases play a critical role in this process by generating the electrochemical gradient to drive solute transport and concomitant water flux. The PM H(+)-ATPase activity is specifically regulated by red and blue light, fungal toxins and auxin. To determine if the unique responsiveness of the guard cell PM H(+)-ATPase is due to the expression of a cell-specific isoform, we amplified by PCR, and cloned portions of PM H(+)-ATPase genes VHA1 and VHA2, which are expressed in guard cell protoplasts (GCP). In situ hybridization to leaf tissue sections indicated that VHA1 and VHA2 genes were expressed in guard cells and mesophyll cells but not in epidermal cells or vascular tissues. Furthermore, a gene-specific quantitative reverse transcription (RT)-PCR detected VHA1 and VHA2 mRNAs in both GCP and mesophyll cell protoplast mRNA as well as in mRNA isolated from roots, leaves, stems and flowers. Thus, two PM H(+)-ATPase genes expressed in guard cells are also expressed in many other tissues and cell types. This suggests that the unique responsiveness of the guard cell PM H(+)-ATPases to environmental stimuli results from cell-specific signal transduction pathways rather than the expression of a cell-specific PM H(+)-ATPase.

Differential Regulation of Gene Expression in the Obligate Biotrophic Interaction of Uromyces fabae with Its Host Vicia faba

“…We confirmed their expression in all vegetative tissues and the dominance of Vf-VHA1 in leaves and of Vf-VHA2 in roots (Hentzen et al 1996). Both were generally down-regulated upon infection (Fig.…”

Blue light activates the plasma membrane H+-ATPase by phosphorylation of the C-terminus in stomatal guard cells

“…Since guard cells respond specifically to BL by activating the plasma membrane H ϩ -ATPase, it is expected that a guard cell-specific isoprotein with a unique regulatory domain catalyses this reaction. In guard cells of V.faba, two mRNAs encoding the H ϩ -ATPase isoproteins (VHA1 and VHA2) are expressed; however, these genes are not unique to guard cells and it is suggested that they are expressed in roots, leaves, stems and flowers (Nakajima et al, 1995;Hentzen et al, 1996). Thus, it is most likely that the H ϩ -ATPase(s) in guard cells are phosphorylated via a guard cell-specific signalling pathway which can respond to BL.…”

“…These results suggest that phosphorylation of plasma membrane H ϩ -ATPase is required for its activation, and that the increased H ϩ -ATPase activity is responsible for BL-dependent H ϩ pumping in GCPs. Figure 5 shows the amino acid sequences of the C-termini of two H ϩ -ATPase isoforms deduced from isogenes of VHA1 and VHA2 expressed in guard cells (Nakajima et al, 1995;Hentzen et al, 1996). Treatment of these H ϩ -ATPases with cyanogen bromide (CNBr), which should split the H ϩ -ATPase polypeptide chains on the carboxyl side of Met782 and Met840, will generate 19.7 and 12.9 kDa of the C-terminal regions from VHA1 (positions 783-956) and VHA2 (position 841-952), respectively, and the other regions of the H ϩ -ATPase will be digested below 12 kDa.…”

“…Two mRNAs encoding the H ϩ -ATPase isoproteins (VHA1 and VHA2, Vicia H ϩ -ATPase isoforms 1 and 2) are expressed in Vicia guard cells, and cDNA clones for these have been isolated (Nakajima et al, 1995;Hentzen et al, 1996). Since the plasma membrane H ϩ -ATPase generates a H ϩ electrochemical gradient, and provides a driving force for the uptake of various nutrients such as K ϩ , nitrate, sulfate, sucrose and amino acids across the plasma membrane in many cell types and tissues of plant, the regulatory mechanism of this enzyme has been studied extensively (Serrano, 1989;Palmgren, 1991;Sussman, 1994;Michelet and Boutry, 1995;Sze et al, 1999).…”

Plant Plasma Membrane H+-ATPase in Adaptation of Plants to Abiotic Stresses

“…It has been shown that various genes are expressed in the same organ. Moreover, even within the same cell type at the same developmental stage, at least two H + -ATPase genes are expressed (Harms et al, 1994;Hentzen et al, 1996;Moriau et al, 1999). In N. plumbaginifolia two different plasma membrane H + -ATPase genes, PMA2 and PMA4, are expressed in guard cells (Moriau et al, 1999).…”