Salt regulation of transcript levels for the c subunit of a leaf vacuolar H⁺‐ATPase in the halophyte Mesembryanthemum crystallinum

Abstract

SummaryThe halophyte Mesembryanthemum crystallinum is an inducible crassulacean acid metabolism (CAM) plant native to seasonally arid coastal environments that has been widely used to study plant responses to environmental stress. On exposure of plants to salt, the activities of both the tonoplast (vacuolar) H+-ATPase (V-ATPase) and Na+/ H + antiporter increase in leaf cells, thereby energizing vacuolar salt accumulation. To investigate the molecular basis of this response, a cDNA (Vmacl) encoding the H +-conducting c subunit (16.6 kDa) of an M. crystallinum V-ATPase has been cloned. Northern analysis of RNA from leaves of plants treated with NaCl or with isoosmotic mannitoL solutions demonstrated (i) that NaCI increased steady-state transcript levels for the V-ATPase c subunit, and (ii) that this effect was caused by the ionic rather than the osmotic component of salt stress. Southern analysis of genomic DNA suggested the probable existence of more than one gene for this subunit of the V-ATPasa in M.crystallinum. Expression studies using the 3"-untranslated region of the Vmacl cDNA as a probe showed that the corresponding salt-inducible transcript was preferentially expressed in leaves. Induction by salt was also observed in juvenile plants in addition to adult ones. These findings, as well as the inability of mannitol to upregulate mRNA levels for this gene, clearly differentiate between the induction of transcript for the V-ATPase c subunit and for genes involved in the CAM pathway in M. crystallinum.Further, the plant growth regulator abscisic acid (ABA) was able to mimic the effect of salt on transcript levels for the V-ATPasa c subunit, suggesting the possible involvement of ABA in a distinct signal-transduction pathway linked to vacuolar salt accumulation in this highly salt-tolerant species.

Inositol(1,4,5)trisphosphate production in plant cells: an early response to salinity and hyperosmotic stress

“…It is known that plants have the ability to discriminate between osmotic and salt stresses [20] but the underlying mechanisms have yet to be identi¢ed. It is now generally recognised that the creation of distinct spatio-temporal Ca 2 pro¢les within cellular microdomains is utilised by mammalian cells to distinguish between both the nature and intensity of a wide range of cellular stimuli [21] and, as has recently been pointed out by several researchers, a similar situation is likely to exist in plant cells [22,23].…”

The vacuolar H+-ATPase: a universal proton pump of eukaryotes

“…The 16-17 kDa subunit c of the V o sector has been widely studied, and the genes from diverse fungal [102,103], plant [104][105][106][107][108][109], arthropod [7,[110][111][112], mammalian [113][114][115] and other vertebrate [116] sources have been cloned. The 16 kDa proteolipid is one of the most conserved membrane proteins known, with greater than 65 % identity between virtually all species (M. E. Finbow and M. A. Harrison, unpublished work).…”

“…However, Drosophila contains a single gene locus encoding a single transcript [111] and, although four genes have been identified in humans, three are thought to be pseudogenes [125]. By contrast, higher plants, which do not have gap junctions but have alternative means of cell-cell communication through plasmadesmata, have multiple genes encoding nearidentical polypeptides [105,106,108,109]. The significance of this multiplicity in plants is unclear.…”

Signaling Events Leading to Crassulacean Acid Metabolism Induction in the Common Ice Plant

“…Salinity and drought stress treatments cause marked increases of endogenous ABA amounts Taybi et al, 1995). Endogenous increases or exogenous application of ABA result in CAM induction (Dai et al, 1994;Taybi et al, 1995) by stimulating increased expression of key CAM enzymes such as PEPC (Chu et al, 1990;Dai et al, 1994;Taybi et al, 1995), enolase (Forsthoefel et al, 1995a), phosphoglyceromutase (Forsthoefel et al, 1995b), and vacuolar ATPase subunit c (Tsiantis et al, 1996). Other plant growth regulators such as cytokinins have been shown to either suppress or enhance PEPC expression depending on the mode of application (Schmitt and Piepenbrock, 1992;Thomas et al, 1992;Thomas and Bohnert, 1993;Dai et al, 1994;Peters et al, 1997).…”