期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：23
页码：7309-7314
DOI：10.1073/pnas.1507810112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceThe Venus flytrap Dionaea muscipula has been in the focus of scientists since Darwin's time. Carnivorous plants, with their specialized lifestyle, including insect capture, as well as digestion and absorption of prey, developed unique tools to gain scarce nutrients. In this study, we identified the molecular nature of the uptake machinery for prey-derived potassium and the posttranslational regulation. For the first time, to our knowledge, we functionally characterize DmHAK5 here--a KUP/HAK/KT family member as activated by a CBL-CIPK kinase complex. Detailed electrophysiological characterization identified DmHAK5 as a proton-driven, high-affinity potassium transporter with a weak selectivity. Working hand-in-hand with the low-affinity, high-capacity K+-channel DmKT1 activated by the same kinase, the transporters allow the Venus flytrap to take up prey-derived potassium. The Darwin plant Dionaea muscipula is able to grow on mineral-poor soil, because it gains essential nutrients from captured animal prey. Given that no nutrients remain in the trap when it opens after the consumption of an animal meal, we here asked the question of how Dionaea sequesters prey-derived potassium. We show that prey capture triggers expression of a K+ uptake system in the Venus flytrap. In search of K+ transporters endowed with adequate properties for this role, we screened a Dionaea expressed sequence tag (EST) database and identified DmKT1 and DmHAK5 as candidates. On insect and touch hormone stimulation, the number of transcripts of these transporters increased in flytraps. After cRNA injection of K+-transporter genes into Xenopus oocytes, however, both putative K+ transporters remained silent. Assuming that calcium sensor kinases are regulating Arabidopsis K+ transporter 1 (AKT1), we coexpressed the putative K+ transporters with a large set of kinases and identified the CBL9-CIPK23 pair as the major activating complex for both transporters in Dionaea K+ uptake. DmKT1 was found to be a K+-selective channel of voltage-dependent high capacity and low affinity, whereas DmHAK5 was identified as the first, to our knowledge, proton-driven, high-affinity potassium transporter with weak selectivity. When the Venus flytrap is processing its prey, the gland cell membrane potential is maintained around -120 mV, and the apoplast is acidified to pH 3. These conditions in the green stomach formed by the closed flytrap allow DmKT1 and DmHAK5 to acquire prey-derived K+, reducing its concentration from millimolar levels down to trace levels.
