Unlike plants, animals rely on rapid nervous systems to escape predation. A stationary fly that perceives danger takes less than 300 ms to take off, and this process requires complex whole- to ion fluxes in cell populations in wounded Arabidopsis plants. As summarised in Supplementary Fig. 1, we show that electrical signalling activates jasmonate biosynthesis in leaves distal to wounds and we identify genes involved in electrical signal propagation. Wound-induced surface potential changesTo investigate patterns of electrical activity and gene expression in 5 week-old rosettes, individual leaves were numbered from oldest to youngest. Electrodes placed on leaf 8 at the midrib/petiole junction (e2 electrode position) and on the petiole (position e3) did not detect changes in electrical activity and such changes were not elicited by walking S. littoralis larvae (Fig. 1b). When recordings were extended, they often showed periodicity ( Supplementary Fig. 3). We used three parameters to characterise these signals: latency (time from wounding to arrival at the amplitude midpoint), amplitude and duration (Fig. 1b). To gain more information on the spread of WASPs within a wounded leaf, four electrodes were placed on the leaf surface (Fig. 1a). After damage, WASPs were detected first at e1, then several seconds later at e2, and finally at e3. An electrode on the lamina also detected damage-elicited electrical activity and, in each case (Fig. 1c), the changes in amplitude were typically close to -70 mV (SupplementaryTable 1). The signals we measured had the same polarity as those produced after a chilling treatment known to cause plasma membrane depolarisation 24,25 . Therefore WASPs in leaf 8 were due to plasma membrane depolarisation ( Supplementary Fig. 4). The WASPs detected on WT plants were indistinguishable to those on wounded plants that lacked the ability to synthesize jasmonates ( Supplementary Fig. 5).This suggests that the mechanism that produces WASPs is upstream or independent of jasmonate synthesis. WASP territories and speedsSignals generated by wounding leaf tips first move towards the centre of the rosette and then disperse away from the apex into a restricted number of distal leaves to initiate distal JA accumulation and signalling 11 . In order to map the spatial distribution of WASPs in the rosette after wounding leaf 8 we placed electrodes in the e3 position of leaves 5 through 18. Leaves 5, 11, 13 and 16 showed responses similar to those in the wounded leaf (Fig. 1d, Supplementary Table 2). For example, after wounding leaf 8, a WASP with a duration of 78±20 s and a peak amplitude of -51 ± 9 mV was reached in leaf 13 after a latency of 66 ± 13 s (n=61 plants). Other leaves (7, 9, 10, 12, 14, 15,17 and 18) showed small positive surface potential changes. For example, leaf 9 showed a 20±5 mV change in surface potential with a latency of 54±12 s (n=46 plants). Most of these observations fit a developmental pattern: In adult-phase Arabidopsis rosettes, leaf 'n' shares direct vascular connections to leave...

Potassium (K +)channel function is fundamental to many physiological processes. However, components and mechanisms regulating the activity of plant K + channels remain poorly understood. Here, we show that the calcium (Ca 2+ ) sensor CBL4 together with the interacting protein kinase CIPK6 modulates the activity and plasma membrane (PM) targeting of the K + channel AKT2 from Arabidopsis thaliana by mediating translocation of AKT2 to the PM in plant cells and enhancing AKT2 activity in oocytes. Accordingly, akt2, cbl4 and cipk6 mutants share similar developmental and delayed flowering phenotypes. Moreover, the isolated regulatory C-terminal domain of CIPK6 is sufficient for mediating CBL4-and Ca 2+-dependent channel translocation from the endoplasmic reticulum membrane to the PM by a novel targeting pathway that is dependent on dual lipid modifications of CBL4 by myristoylation and palmitoylation. Thus, we describe a critical mechanism of ion-channel regulation where a Ca 2+ sensor modulates K + channel activity by promoting a kinase interaction-dependent but phosphorylation-independent translocation of the channel to the PM.

Summary Grapevine (Vitis vinifera), the genome sequence of which has recently been reported, is considered as a model species to study fleshy fruit development and acid fruit physiology. Grape berry acidity is quantitatively and qualitatively affected upon increased K+ accumulation, resulting in deleterious effects on fruit (and wine) quality. Aiming at identifying molecular determinants of K+ transport in grapevine, we have identified a K+ channel, named VvK1.1, from the Shaker family. In silico analyses indicated that VvK1.1 is the grapevine counterpart of the Arabidopsis AKT1 channel, known to dominate the plasma membrane inward conductance to K+ in root periphery cells, and to play a major role in K+ uptake from the soil solution. VvK1.1 shares common functional properties with AKT1, such as inward rectification (resulting from voltage sensitivity) or regulation by calcineurin B‐like (CBL)‐interacting protein kinase (CIPK) and Ca2+‐sensing CBL partners (shown upon heterologous expression in Xenopus oocytes). It also displays distinctive features such as activation at much more negative membrane voltages or expression strongly sensitive to drought stress and ABA (upregulation in aerial parts, downregulation in roots). In roots, VvK1.1 is mainly expressed in cortical cells, like AKT1. In aerial parts, VvK1.1 transcripts were detected in most organs, with expression levels being the highest in the berries. VvK1.1 expression in the berry is localized in the phloem vasculature and pip teguments, and displays strong upregulation upon drought stress, by about 10‐fold.VvK1.1 could thus play a major role in K+ loading into berry tissues, especially upon drought stress.

SUMMARYThe grape berry provides a model for investigating the physiology of non-climacteric fruits. Increased K + accumulation in the berry has a strong negative impact on fruit acidity (and quality). In maturing berries, we identified a K + channel from the Shaker family, VvK1.2, and two CBL-interacting protein kinase (CIPK)/calcineurin B-like calcium sensor (CBL) pairs, VvCIPK04-VvCBL01 and VvCIPK03-VvCBL02, that may control the activity of this channel. VvCBL01 and VvCIPK04 are homologues of Arabidopsis AtCBL1 and AtCIPK23, respectively, which form a complex that controls the activity of the Shaker K + channel AKT1 in Arabidopsis roots. VvK1.2 remained electrically silent when expressed alone in Xenopus oocytes, but gave rise to K + currents when co-expressed with the pairs VvCIPK03-VvCBL02 or VvCIPK04-VvCBL01, the second pair inducing much larger currents than the first one. Other tested CIPK-CBL pairs expressed in maturing berries were found to be unable to activate VvK1.2. When activated by its CIPK-CBL partners, VvK1.2 acts as a voltagegated inwardly rectifying K + channel that is activated at voltages more negative than -100 mV and is stimulated upon external acidification. This channel is specifically expressed in the berry, where it displays a very strong induction at veraison (the inception of ripening) in flesh cells, phloem tissues and perivascular cells surrounding vascular bundles. Its expression in these tissues is further greatly increased upon mild drought stress. VvK1.2 is thus likely to mediate rapid K + transport in the berry and to contribute to the extensive reorganization of the translocation pathways and transport mechanisms that occurs at veraison.