April 2017, Volume 59 Issue 4, Pages 229每287.

Cover Caption: Tonoplast targeting of V-ATPase
Similar to the transportation network in a city, the dynamic trafficking of membrane proteins is crucial for a cell to function properly. In this issue, Feng et al. (230-233) demonstrate that tonoplast associated V-ATPase is transported through a Rab5-mediated but Rab7- independent pathway, suggesting the presence of a non-conventional vacuolar trafficking route in plant cells.


          Letters to the Editor
Tonoplast targeting of VHA-a3 relies on a Rab5-mediated but Rab7-independent vacuolar trafficking route  
Author: Qiang-Nan Feng, Yan Zhang and Sha Li
Journal of Integrative Plant Biology 2017 59(4): 230每233
Published Online: February 15, 2017
DOI: 10.1111/jipb.12526

Vacuolar trafficking routes and their regulators have recently drawn lots of attention in plant cell biology. A recent study reported the discovery of a plant-specific vacuolar trafficking route, i.e., a direct ER-to-vacuole route, through analysis of VHA-a3 subcellular targeting, a key component for the tonoplast V-ATPases. Our recent findings showed that VHA-a3 targets to the tonoplast through a Rab5-mediated but Rab7-independent pathway, shedding new lights on the unconventional vacuolar trafficking route in plant cells.

Abstract (Browse 491)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Dynamic trafficking of membrane proteins is crucial for cells to function properly, not unlike a transportation network linking all locations within a city. Understanding regulators in these trafficking routes is thus an important topic. This study reveals a regulatory route through which the tonoplast-associated V-ATPase is transported in Arabidopsis.
BIK1 cooperates with BAK1 to regulate constitutive immunity and cell death in Arabidopsis  
Author: Jun Liu, Sufen Chen, Lijuan Chen, Qi Zhou, Menglong Wang, Dongru Feng, Jian-Feng Li, Jinfa Wang, Hong-Bin Wang and Bing Liu
Journal of Integrative Plant Biology 2017 59(4): 234每239
Published Online: February 22, 2017
DOI: 10.1111/jipb.12529

In Arabidopsis, both the membrane-anchored receptor-like kinase (RLK) BAK1 and the receptor-like cytoplasmic kinase (RLCK) BIK1 are important mediators of transmembrane signal transduction that regulate plant development and immunity. However, little attention has been paid to their genetic association. This study found the bak1 bik1 double mutant of Arabidopsis displayed a severe dwarfism phenotype due to constitutive immunity and cell death in developing plants. These data suggest that BIK1 cooperates with BAK1 to regulate constitutive immunity and cell death.

Abstract (Browse 555)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
bak1 bik1 double mutants showed a severe dwarfism phenotype. The constitutive immune activation was mainly responsible for the cell death and developmental defects in bak1 bik1 double mutants. This study indicated that BAK1 and BIK1 are critical for regulation of the constitutive immune response and cell death in Arabidopsis.
          Invited Expert Review
What are the evolutionary origins of stomatal responses to abscisic acid in land plants?  
Author: Frances C. Sussmilch, Timothy J. Brodribb and Scott A. M. McAdam
Journal of Integrative Plant Biology 2017 59(4): 240每260
Published Online: January 17, 2017
DOI: 10.1111/jipb.12523

The evolution of active stomatal closure in response to leaf water deficit, mediated by the hormone abscisic acid (ABA), has been the subject of recent debate. Two different models for the timing of the evolution of this response recur in the literature. A single-step model for stomatal control suggests that stomata evolved active, ABA-mediated control of stomatal aperture, when these structures first appeared, prior to the divergence of bryophyte and vascular plant lineages. In contrast, a gradualistic model for stomatal control proposes that the most basal vascular plant stomata responded passively to changes in leaf water status. This model suggests that active ABA-driven mechanisms for stomatal responses to water status instead evolved after the divergence of seed plants, culminating in the complex, ABA-mediated responses observed in modern angiosperms. Here we review the findings that form the basis for these two models, including recent work that provides critical molecular insights into resolving this intriguing debate, and find strong evidence to support a gradualistic model for stomatal evolution.

Abstract (Browse 883)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
This review examines when active, ABA-mediated mechanisms for control of stomatal aperture evolved in land plants, allowing improved plant survival in dry terrestrial environments. The evidence for two prominent and opposing models is outlined with recent findings strongly supporting the gradual evolution of ABA-driven control from passive ancestral responses.
          Molecular Physiology
Transition from a maternal to external nitrogen source in maize seedlings  
Author: Kasra Sabermanesh, Luke R. Holtham, Jessey George, Ute Roessner, Berin A. Boughton, Sigrid Heuer, Mark Tester, Darren C. Plett and Trevor P. Garnett
Journal of Integrative Plant Biology 2017 59(4): 261每274
Published Online: February 7, 2017
DOI: 10.1111/jipb.12525

Maximizing NO3 uptake during seedling development is important as it has a major influence on plant growth and yield. However, little is known about the processes leading to, and involved in, the initiation of root NO3 uptake capacity in developing seedlings. This study examines the physiological processes involved in root NO3 uptake and metabolism, to gain an understanding of how the NO3 uptake system responds to meet demand as maize seedlings transition from seed N use to external N capture. The concentrations of seed-derived free amino acids within root and shoot tissues are initially high, but decrease rapidly until stabilizing eight days after imbibition (DAI). Similarly, shoot N% decreases, but does not stabilize until 12–13 DAI. Following the decrease in free amino acid concentrations, root NO3 uptake capacity increases until shoot N% stabilizes. The increase in root NO3 uptake capacity corresponds with a rapid rise in transcript levels of putative NO3 transporters, ZmNRT2.1 and ZmNRT2.2. The processes underlying the increase in root NO3 uptake capacity to meet N demand provide an insight into the processes controlling N uptake.

Abstract (Browse 414)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Root NO3 uptake capacity is regulated to meet plant nitrogen demand. To develop a model detailing it, we exploited a seedling's transition from seed nitrogen use to external nitrogen capture.
          Plant-environmental Interactions
ORA59 and EIN3 interaction couples jasmonate-ethylene synergistic action to antagonistic salicylic acid regulation of PDF expression  
Author: Xiang He, Jishan Jiang, Changquan Wang and Katayoon Dehesh
Journal of Integrative Plant Biology 2017 59(4): 275每287
Published Online: February 7, 2017
DOI: 10.1111/jipb.12524

Hormonal crosstalk is central for tailoring plant responses to the nature of challenges encountered. The role of antagonism between the two major defense hormones, salicylic acid (SA) and jasmonic acid (JA), and modulation of this interplay by ethylene (ET) in favor of JA signaling pathway in plant stress responses is well recognized, but the underlying mechanism is not fully understood. Here, we show the opposing function of two transcription factors, ethylene insensitive3 (EIN3) and EIN3-Like1 (EIL1), in SA-mediated suppression and JA-mediated activation of PLANT DEFENSIN1.2 (PDF1.2). This functional duality is mediated via their effect on protein, not transcript levels of the PDF1.2 transcriptional activator octadecanoid-responsive Arabidopsis59 (ORA59). Specifically, JA induces ORA59 protein levels independently of EIN3/EIL1, whereas SA reduces the protein levels dependently of EIN3/EIL1. Co-infiltration assays revealed nuclear co-localization of ORA59 and EIN3, and split-luciferase together with yeast-two-hybrid assays established their physical interaction. The functional ramification of the physical interaction is EIN3-dependent degradation of ORA59 by the 26S proteasome.

These findings allude to SA-responsive reduction of ORA59 levels mediated by EIN3 binding to and targeting of ORA59 for degradation, thus nominating ORA59 pool as a coordination node for the antagonistic function of ET/JA and SA.

Abstract (Browse 1003)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
SA treatment promotes EIN3 binding and targeting to ORA59 for degradation, whereas JA promotes EIN3 transactivation of ORA59 and induction of PDF1.2 Thus ORA59 acts as a coordinating node for the antagonistic function of ET/JA and SA.
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