Identification of a Nicotiana plumbaginifolia plasma membrane H + -ATPase gene expressed in the pollen tube w Benoit Lefebvre, Miguel Arango, Mohammed Oufattole, Je´roˆme Crouzet, Be´ne´dicte Purnelle and Marc Boutry* Unite ´ de biochimie physiologique, Institut des sciences de la vie, Universite´ catholique de Louvain, Croix du Sud 2-20, B-1348, Louvain-la-Neuve, Belgium (*author for correspondence; e-mail boutry@fysa.ucl.ac.be) Received 8 December 2004; accepted in revised form 25 May 2005 Key words: asymmetric distribution, H + -ATPase, plasma membrane, pollen, pollen tube, transport Abstract In Nicotiana plumbaginifolia, plasma membrane H + -ATPases (PMAs) are encoded by a gene family of nine members. Here, we report on the characterization of a new isogene, NpPMA5 (belonging to subfamily IV), and the determination of its expression pattern using the b-glucuronidase (gusA) reporter gene. pNpPMA5– gusA was expressed in cotyledons, in vascular tissues of the stem (mainly in nodal zones), and in the flower and fruit. In the flower, high expression was found in the pollen tube after in vitro or in vivo germination. Northern blotting analysis confirmed that NpPMA5 was expressed in the pollen tube contrary to NpPMA2 (subfamily I) or NpPMA4 (subfamily II), two genes highly expressed in other tissues. The subcellular localization of PM H + -ATPase in the pollen tube was analyzed by immunocytodecoration. As expected, this enzyme was localized to the plasma membrane. However, neither the tip nor the base of the pollen tube was labeled, showing an asymmetrical distribution of this enzyme. This observation supports the hypothesis that the PM H + -ATPase is involved in creating the pH gradient that is observed along the pollen tube and is implicated in cell elongation. Compared to other plant PM H + -ATPases, the C-terminal region of NpPMA5 is shorter by 26 amino acid residues and is modified in the last 6 residues, due to a sequence rearrangement, which was also found in the orthologous gene of Nicotiana glutinosa,a Nicotiana species distant from N. plumbaginifolia and Petunia hybrida and Lycopersicon esculentum, other Solanacae species. This modification alters part of the PM H + -ATPase regulatory domain and raises the question whether this isoform is still regulated. Introduction Solute accumulation and exclusion in the cell are controlled by transporters embedded in the plasma membrane. The plasma membrane proton pump ATPase (PM H + -ATPase) plays a key role in transport processes across the plasma membrane, since, as a primary transporter, it pumps protons out of the cell, creating a H + electrochemical gradient across the membrane. This chemiosmotic energy is the motive force for a large set of secondary transporters which move their sub- strates against a concentration gradient. The PM H + -ATPase is therefore involved in many physi- ological functions, such as mineral absorption from the soil, changes in stomatal aperture, and phloem transport. It is also suggested to be involved in processes such as cytoplasmic pH w The genomic and cDNA nucleotide sequences of NpPMA5 have been deposited into the Genbank database (AY772462–AY772468). Plant Molecular Biology (2005) 58:775–787 Ó Springer 2005 DOI 10.1007/s11103-005-7875-3