Gallium(III)- and calcium(II)-catalyzed Meyer–Schuster rearrangements followed by intramolecular aldol condensation or endo-Michael addition

The first gallium- and calcium-catalyzed Meyer–Schuster rearrangements are described. The incipient conjugated ketones can undergo calcium-catalyzed aldol condensation (a) or endo-Michael addition (b) with β-keto esters or amides.

Expression analysis of two gene subfamilies encoding the plasma membrane H+-ATPase in Nicotiana plumbaginifolia reveals the major transport functions of this enzyme

The plasma membrane H+-ATPase couples ATP hydrolysis to proton transport, thereby establishing the driving force for solute transport across the plasma membrane. In Nicotiana plumbaginifolia, this enzyme is encoded by at least nine pma (plasma membrane H+-ATPase) genes. Four of these are classified into two gene subfamilies, pma1-2-3 and pma4, which are the most highly expressed in plant species. We have isolated genomic clones for pma2 and pma4. Mapping of their transcript 5' end revealed the presence of a long leader that contained small open reading frames, regulatory features typical of other pma genes. The gusA reporter gene was then used to determine the expression of pma2, pma3 and pma4 in N. tabacum. These data, together with those obtained previously for pma1, led to the following conclusions. (i) The four pma-gusA genes were all expressed in root, stem, leaf and flower organs, but each in a cell-type specific manner. Expression in these organs was confirmed at the protein level, using subfamily-specific antibodies. (ii) pma4-gusA was expressed in many cell types and notably in root hair and epidermis, in companion cells, and in guard cells, indicating that in N. plumbaginifolia the same H+-ATPase isoform might be involved in mineral nutrition, phloem loading and control of stomata aperture. (iii) The second gene subfamily is composed, in N. plumbaginifolia, of a single gene (pma4) with a wide expression pattern and, in Arabidopsis thaliana, of three genes (aha1, aha2, aha3), at least two of them having a more restrictive expression pattern. (iv) Some cell types expressed pma2 and pma4 at the same time, which encode H+-ATPases with different enzymatic properties.

A plant plasma membrane proton-ATPase gene is regulated by development and environment and shows signs of a translational regulation

A proton-pumping ATPase is present in the plasma membrane of plant cells where it sustains transport-related functions. This enzyme is encoded by a family of genes that shows signs of both transcriptional and post-transcriptional regulation. The regulation of pma1, one of the Nicotiana plumbaginifolia H+-ATPase genes, was characterized with the help of the beta-glucuronidase (gusA) receptor gene in transgenic plants. pma1 is active in the root epidermis, the stem cortex, and guard cells. This activity depends on developmental and growth conditions. For instance, pma1 activity in guard cells was strongly enhanced when the plant material (young seedlings or mature leaves) was incubated in liquid growth medium. pma1 is also expressed in several tissues of the reproductive organs where active transport is thought to occur but where scarcely any ATPase activity has been identified, namely in the tapetum, the pollen, the transmitting tissue, and the ovules. Several pma genes have a long 5'untranslated region (leader sequence) containing an upstream open reading frame (URF). Analysis of translational and transcriptional fusions with gusA in transgenic plants suggests that the pma1 leader sequence might activate translation of the main open reading frame, even though the URF is translated by a large majority of the scanning ribosomes. As confirmation, transient expression experiments showed that the pma1 leader causes a fourfold post-transcriptional increase of main open reading frame expression. Deletion of the URF by site-directed mutagenesis stimulated the main open reading frame translation 2.7-fold in an in vitro translational assay. These results are consistent with a regulatory mechanism involving translation reinitiation. Altogether, they suggest a fine, multilevel regulation of H+-ATPase activity in the plant.

Differential expression within a three-gene subfamily encoding a plasma membrane H(+)-ATPase in Nicotiana plumbaginifolia

Genomic and cDNA clones for the three members of a gene subfamily (pma) encoding a plasma membrane H(+)-translocating ATPase in Nicotiana plumbaginifolia were isolated and sequenced. They are between 95 and 96% identical at the deduced amino acid sequence level. Sequence comparisons with the corresponding tomato genes (Ewing, N.N., Wimmers, L.E., Meyer, D.J., Chetelat, R.T., and Bennett, A.B. (1990) Plant Physiol. 94, 1874-1881) indicate that divergence among the three N. plumbaginifolia pma genes occurred before the development of the Solanaceae family. Here, determination of pma1 transcription initiation sites reveals several 5' boundaries located 266 to 120 nucleotides upstream from the plasma membrane H(+)-ATPase translation initiation codon. The 5'-untranslated region contains a small open reading frame, 9 residues long. pma3 has a single, 264-nucleotide long 5' leader containing a 5-residue open reading frame. The latter is completely conserved in a corresponding tomato gene. These features suggest the possibility of translational regulation of plant pma genes. S1 nuclease protection assays on total cellular RNA isolated from different organs reveals that all three genes are expressed in leaf, stem, flower, and root tissues, albeit at different levels according to the organ and gene. The different genes for the plant H(+)-translocating ATPase are thus subject to differential regulation of transcription, possibly related to specific aspects of enzyme function.

Molecular cloning of a family of plant genes encoding a protein homologous to plasma membrane H+-translocating ATPases

cDNA clones from Nicotiana plumbaginifolia have been isolated by hybridization to a yeast H+-ATPase gene. The largest one encodes a polypeptide (PMA2) of 956 amino acid residues which exhibits a homology of 73% with a limited protein sequence obtained from purified oat plasma membrane H+-ATPase (Schaller and Sussman, Plant Physiol. 86, 512-516, 1988) and an 82% homology with the Arabidopsis thaliana pma gene (Harper et al., Proc. Natl. Acad. Sci. USA 86, 1234-1238). It is therefore concluded that the N. plumbaginifolia pma2 gene encodes a plasma membrane H+-ATPase. Southern blot hybridization indicates that the plant pma2 gene belongs to a multigene family. Partial sequences of cDNA clones show that at least three pma genes are expressed in root cells.