<i>MRF</i> Family Genes Are Involved in Translation Control, Especially under Energy-Deficient Conditions, and Their Expression and Functions Are Modulated by the TOR Signaling Pathway

Lee, Du-Hwa,Park, Seung Jun,Ahn, Chang Sook,Pai, Hyun-Sook Americ 2017 The Plant cell Vol.29 No.11

<P><I>MRF</I> family genes encode translation regulatory factors, with functions that are important under energy-deficient conditions, and the TOR signaling pathway modulates MRF expression and functions.</P><P>Dynamic control of protein translation in response to the environment is essential for the survival of plant cells. Target of rapamycin (TOR) coordinates protein synthesis with cellular energy/nutrient availability through transcriptional modulation and phosphorylation of the translation machinery. However, mechanisms of TOR-mediated translation control are poorly understood in plants. Here, we report that <I>Arabidopsis thaliana MRF</I> (MA3 DOMAIN-CONTAINING TRANSLATION REGULATORY FACTOR) family genes encode translation regulatory factors under TOR control, and their functions are particularly important in energy-deficient conditions. Four <I>MRF</I> family genes (<I>MRF1</I>-<I>MRF4</I>) are transcriptionally induced by dark and starvation (DS). Silencing of multiple <I>MRFs</I> increases susceptibility to DS and treatment with a TOR inhibitor, while <I>MRF1</I> overexpression decreases susceptibility. MRF proteins interact with eIF4A and cofractionate with ribosomes. <I>MRF</I> silencing decreases translation activity, while <I>MRF1</I> overexpression increases it, accompanied by altered ribosome patterns, particularly in DS. Furthermore, MRF deficiency in DS causes altered distribution of mRNAs in sucrose gradient fractions and accelerates rRNA degradation. MRF1 is phosphorylated in vivo and phosphorylated by S6 kinases in vitro. <I>MRF</I> expression and MRF1 ribosome association and phosphorylation are modulated by cellular energy status and TOR activity. We discuss possible mechanisms of the function of MRF family proteins under normal and energy-deficient conditions and their functional link with the TOR pathway.</P>

Spatial Regulation of ABCG25, an ABA Exporter, Is an Important Component of the Mechanism Controlling Cellular ABA Levels

Park, Youngmin,Xu, Zheng-Yi,Kim, Soo Youn,Lee, Jihyeong,Choi, Bongsoo,Lee, Juhun,Kim, Hyeran,Sim, Hee-Jung,Hwang, Inhwan Americ 2016 The Plant cell Vol.28 No.10

<P>The phytohormone abscisic acid (ABA) plays crucial roles in various physiological processes, including responses to abiotic stresses, in plants. Recently, multiple ABA transporters were identified. The loss-of-function and gain-of-function mutants of these transporters show altered ABA sensitivity and stomata regulation, highlighting the importance of ABA transporters in ABA-mediated processes. However, how the activity of these transporters is regulated remains elusive. Here, we show that spatial regulation of ATP BINDING CASETTE G25 (ABCG25), an ABA exporter, is an important mechanism controlling its activity. ABCG25, as a soluble green fluorescent protein (sGFP) fusion, was subject to posttranslational regulation via clathrin-dependent and adaptor protein complex-2-dependent endocytosis followed by trafficking to the vacuole. The levels of sGFP: ABCG25 at the plasma membrane (PM) were regulated by abiotic stresses and exogenously applied ABA; PM-localized sGFP: ABCG25 decreased under abiotic stress conditions via activation of endocytosis in an ABA-independent manner, but increased upon application of exogenous ABA via activation of recycling from early endosomes in an ABA-dependent manner. Based on these findings, we propose that the spatial regulation of ABCG25 is an important component of the mechanism by which plants fine-tune cellular ABA levels according to cellular and environmental conditions.</P>

SIZ1-mediated sumoylation of ICE1 controls CBF3/DREB1A expression and freezing tolerance in Arabidopsis.

Miura, Kenji,Jin, Jing Bo,Lee, Jiyoung,Yoo, Chan Yul,Stirm, Vicki,Miura, Tomoko,Ashworth, Edward N,Bressan, Ray A,Yun, Dae-Jin,Hasegawa, Paul M Americ 2007 The Plant cell Vol.19 No.4

<P>SIZ1 is a SUMO E3 ligase that facilitates conjugation of SUMO to protein substrates. siz1-2 and siz1-3 T-DNA insertion alleles that caused freezing and chilling sensitivities were complemented genetically by expressing SIZ1, indicating that the SIZ1 is a controller of low temperature adaptation in plants. Cold-induced expression of CBF/DREB1, particularly of CBF3/DREB1A, and of the regulon genes was repressed by siz1. siz1 did not affect expression of ICE1, which encodes a MYC transcription factor that is a controller of CBF3/DREB1A. A K393R substitution in ICE1 [ICE1(K393R)] blocked SIZ1-mediated sumoylation in vitro and in protoplasts identifying the K393 residue as the principal site of SUMO conjugation. SIZ1-dependent sumoylation of ICE1 in protoplasts was moderately induced by cold. Sumoylation of recombinant ICE1 reduced polyubiquitination of the protein in vitro. ICE1(K393R) expression in wild-type plants repressed cold-induced CBF3/DREB1A expression and increased freezing sensitivity. Furthermore, expression of ICE1(K393R) induced transcript accumulation of MYB15, which encodes a MYB transcription factor that is a negative regulator of CBF/DREB1. SIZ1-dependent sumoylation of ICE1 may activate and/or stabilize the protein, facilitating expression of CBF3/DREB1A and repression of MYB15, leading to low temperature tolerance.</P>

Cytokinin-Mediated Regulation of Reactive Oxygen Species Homeostasis Modulates Stomatal Immunity in Arabidopsis

Arnaud, Dominique,Lee, Seungchul,Takebayashi, Yumiko,Choi, Daeseok,Choi, Jaemyung,Sakakibara, Hitoshi,Hwang, Ildoo Americ 2017 The Plant cell Vol.29 No.3

<P>Stomata play an important role in preinvasive defense responses by limiting pathogen entry into leaves. Although the stress hormones salicylic acid (SA) and abscisic acid (ABA) are known to regulate stomatal immunity, the role of growth promoting hormones is far from understood. Here, we show that in Arabidopsis thaliana, cytokinins (CKs) function in stomatal defense responses. The cytokinin receptor HISTIDINE KINASE3 (AHK3) and RESPONSE REGULATOR2 (ARR2) promote stomatal closure triggered by pathogen-associated molecular pattern (PAMP) and resistance to Pseudomonas syringae pv tomato bacteria. Importantly, the cytokinin trans-zeatin induces stomatal closure and accumulation of reactive oxygen species (ROS) in guard cells through AHK3 and ARR2 in an SA-dependent and ABA-independent manner. Using pharmacological and reverse genetics approaches, we found that CK-mediated stomatal responses involve the apoplastic peroxidases PRX4, PRX33, PRX34, and PRX71, but not the NADPH oxidases RBOHD and RBOHF. Moreover, ARR2 directly activates the expression of PRX33 and PRX34, which are required for SA-and PAMP-triggered ROS production. Thus, the CK signaling pathway regulates ROS homeostasis in guard cells, which leads to enhanced stomatal immunity and plant resistance to bacteria.</P>

ZEITLUPE Contributes to a Thermoresponsive Protein Quality Control System in Arabidopsis

Gil, Kyung-Eun,Kim, Woe-Yeon,Lee, Hyo-Jun,Faisal, Mohammad,Saquib, Quaiser,Alatar, Abdulrahman A.,Park, Chung-Mo Americ 2017 The Plant cell Vol.29 No.11

<P>The E3 ligase ZEITLUPE mediates the clearance of denatured protein aggregates under heat stress conditions, thereby enhancing thermotolerance and the thermal stability of the circadian clock.</P><P>Cellular proteins undergo denaturation and oxidative damage under heat stress, forming insoluble aggregates that are toxic to cells. Plants possess versatile mechanisms to deal with insoluble protein aggregates. Denatured proteins are either renatured to their native conformations or removed from cellular compartments; these processes are often referred to as protein quality control. Heat shock proteins (HSPs) act as molecular chaperones that assist in the renaturation-degradation process. However, how protein aggregates are cleared from cells in plants is largely unknown. Here, we demonstrate that heat-induced protein aggregates are removed by a protein quality control system that includes the ZEITLUPE (ZTL) E3 ubiquitin ligase, a central circadian clock component in <I>Arabidopsis thaliana</I>. ZTL mediates the polyubiquitination of aggregated proteins, which leads to proteasomal degradation and enhances the thermotolerance of plants growing at high temperatures. The ZTL-defective <I>ztl-105</I> mutant exhibited reduced thermotolerance, which was accompanied by a decline in polyubiquitination but an increase in protein aggregate formation. ZTL and its interacting partner HSP90 were cofractionated with insoluble aggregates under heat stress, indicating that ZTL contributes to the thermoresponsive protein quality control machinery. Notably, the circadian clock was hypersensitive to heat in <I>ztl-105</I>. We propose that ZTL-mediated protein quality control contributes to the thermal stability of the circadian clock.</P>

SH3 Domain-Containing Protein 2 Plays a Crucial Role at the Step of Membrane Tubulation during Cell Plate Formation

Ahn, Gyeongik,Kim, Hyeran,Kim, Dae Heon,Hanh, Hong,Yoon, Youngdae,Singaram, Indira,Wijesinghe, Kaveesha J.,Johnson, Kristen A.,Zhuang, Xiaohong,Liang, Zizhen,Stahelin, Robert V.,Jiang, Liwen,Cho, Wonh Americ 2017 The Plant cell Vol.29 No.6

<P>During cytokinesis in plants, trans-Golgi network-derived vesicles accumulate at the center of dividing cells and undergo various structural changes to give rise to the planar cell plate. However, how this conversion occurs at the molecular level remains elusive. In this study, we report that SH3 Domain-Containing Protein 2 (SH3P2) in Arabidopsis thaliana plays a crucial role in converting vesicles to the planar cell plate. SH3P2 RNAi plants showed cytokinesis-defective phenotypes and produced aggregations of vesicles at the leading edge of the cell plate. SH3P2 localized to the leading edge of the cell plate, particularly the constricted or curved regions of the cell plate. The BAR domain of SH3P2 induced tubulation of vesicles. SH3P2 formed a complex with dynamin-related protein 1A (DRP1A) and affected DRP1A accumulation to the cell plate. Based on these results, we propose that SH3P2 functions together with DRP1A to convert the fused vesicles to tubular structures during cytokinesis.</P>

Arabidopsis nuclear-encoded plastid transit peptides contain multiple sequence subgroups with distinctive chloroplast-targeting sequence motifs.

Lee, Dong Wook,Kim, Jong Kyoung,Lee, Sumin,Choi, Seungjin,Kim, Sanguk,Hwang, Inhwan Americ 2008 The Plant cell Vol.20 No.6

<P>The N-terminal transit peptides of nuclear-encoded plastid proteins are necessary and sufficient for their import into plastids, but the information encoded by these transit peptides remains elusive, as they have a high sequence diversity and lack consensus sequences or common sequence motifs. Here, we investigated the sequence information contained in transit peptides. Hierarchical clustering on transit peptides of 208 plastid proteins showed that the transit peptide sequences are grouped to multiple sequence subgroups. We selected representative proteins from seven of these multiple subgroups and confirmed that their transit peptide sequences are highly dissimilar. Protein import experiments revealed that each protein contained transit peptide-specific sequence motifs critical for protein import into chloroplasts. Bioinformatics analysis identified sequence motifs that were conserved among members of the identified subgroups. The sequence motifs identified by the two independent approaches were nearly identical or significantly overlapped. Furthermore, the accuracy of predicting a chloroplast protein was greatly increased by grouping the transit peptides into multiple sequence subgroups. Based on these data, we propose that the transit peptides are composed of multiple sequence subgroups that contain distinctive sequence motifs for chloroplast targeting.</P>

Steam-Chest Molding of Expanded Polypropylene Foams. 1. DSC Simulation of Bead Foam Processing

김영욱 AMER CHEMICAL SOC 2010 INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH - Vol.49 No.20

Transfer of Magnitude and Spatial Mappings to the SNARC Effect for Parity Judgments

GEN,최준식 AMER PSYCHOLOGICAL ASSOC 2009 JOURNAL OF EXPERIMENTAL PSYCHOLOGY-LEARNING MEMORY Vol.35 No.6

Conditioning-Induced Attentional Bias for Face Stimuli Measured With the Emotional Stroop Task

김현택,이강희,한재현,김민식,최준식 AMER PSYCHOLOGICAL ASSOC 2009 EMOTION - Vol.9 No.1