SLAH 3‐type anion channel expressed in poplar secretory epithelia operates in calcium kinase CPK ‐autonomous manner

• Published in: The New phytologist 2016-05, Vol.210 (3), p.922-933
• Main Authors: Jaborsky, Mario, Maierhofer, Tobias, Olbrich, Andrea, Escalante‐Pérez, María, Müller, Heike M., Simon, Judy, Krol, Elzbieta, Cuin, Tracey Ann, Fromm, Jörg, Ache, Peter, Geiger, Dietmar, Hedrich, Rainer
• Format: Article
• Language: English
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/nph.13841

Extrafloral nectaries secrete a sweet sugar cocktail that lures predator insects for protection from foraging herbivores. Apart from sugars and amino acids, the nectar contains the anions chloride and nitrate. Recent studies with Populus have identified a type of nectary covered by apical bipolar epidermal cells, reminiscent of the secretory brush border epithelium in animals. Border epithelia operate transepithelial anion transport, which is required for membrane potential and/or osmotic adjustment of the secretory cells. In search of anion transporters expressed in extrafloral nectaries, we identified Ptt SLAH 3 ( Populus tremula  ×  Populus tremuloides SLAC 1 Homologue3), an anion channel of the SLAC / SLAH family. When expressed in Xenopus oocytes, Ptt SLAH 3 displayed the features of a voltage‐dependent anion channel, permeable to both nitrate and chloride. In contrast to the Arabidopsis SLAC / SLAH family members, the poplar isoform Ptt SLAH 3 is independent of phosphorylation activation by protein kinases. To understand the basis for the autonomous activity of the poplar SLAH 3, we generated and expressed chimera between kinase‐independent Ptt SLAH 3 and kinase‐dependent Arabidopsis At SLAH 3. We identified the N‐terminal tail and, to a lesser extent, the C‐terminal tail as responsible for Ptt SLAH 3 kinase‐(in)dependent action. This feature of Ptt SLAH 3 may provide the secretory cell with a channel probably controlling long‐term nectar secretion.