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Miyawaki K.N.,Shanghai Center for Plant Stress Biology | Yang Z.,University of California at Riverside
Frontiers in Plant Science | Year: 2014

Rho-like GTPase from plants (ROPs) function as signaling switches that control a wide variety of cellular functions and behaviors including cell morphogenesis, cell division and cell differentiation. The Arabidopsis thaliana genome encodes 11 ROPs that form a distinct single subfamily contrarily to animal or fungal counterparts where multiple subfamilies of Rho GTPases exist. Since Rho proteins bind to their downstream effector proteins only in their GTP-bound “active” state, the activation of ROPs by upstream factor(s) is a critical step in the regulation of ROP signaling. Therefore, it is critical to examine the input signals that lead to the activation of ROPs. Recent findings showed that the plant hormone auxin is an important signal for the activation of ROPs during pavement cell morphogenesis as well as for other developmental processes. In contrast to auxin, another plant hormone, abscisic acid, negatively regulates ROP signaling. Calcium is another emerging signal in the regulation of ROP signaling. Several lines of evidence indicate that plasma membrane localized-receptor like kinases play a critical role in the transmission of the extracellular signals to intracellular ROP signaling pathways. This review focuses on how these signals impinge upon various direct regulators of ROPs to modulate various plant processes. © 2014 Miyawaki and Yang. Source

Guan Y.,University of Missouri | Guan Y.,Shanghai Center for Plant Stress Biology | Lu J.,Zhejiang University | Xu J.,Zhejiang University | And 2 more authors.
Plant Physiology | Year: 2014

Double fertilization in flowering plants requires the delivery of two immotile sperm cells to the female gametes by a pollen tube, which perceives guidance cues, modifies its tip growth direction, and eventually enters the micropyle of the ovule. In spite of the recent progress, so far, little is known about the signaling events in pollen tubes in response to the guidance cues. Here, we show that MPK3 and MPK6, two Arabidopsis (Arabidopsis thaliana) mitogen-activated protein kinases, mediate the guidance response in pollen tubes. Genetic analysis revealed that mpk3 mpk6 double mutant pollen has reduced transmission. However, direct observation of mpk3 mpk6 mutant pollen phenotype was hampered by the embryo lethality of double homozygous mpk3-/- mpk6-/- plants. Utilizing a fluorescent reporter-tagged complementation method, we showed that the mpk3 mpk6 mutant pollen had normal pollen tube growth but impaired pollen tube guidance. In vivo pollination assays revealed that the mpk3 mpk6 mutant pollen tubes were defective in the funicular guidance phase. By contrast, semi-in vitro guidance assay showed that the micropylar guidance of the double mutant pollen tube was normal. Our results provide direct evidence to support that the funicular guidance phase of the pollen tube requires an in vivo signaling mechanism distinct from the micropyle guidance. Moreover, our finding opened up the possibility that the MPK3/MPK6 signaling pathway may link common signaling networks in plant stress response and pollen-pistil interaction. © 2014 American Society of Plant Biologists. All Rights Reserved. Source

Muller D.,University of York | Waldie T.,University of Cambridge | Miyawaki K.,University of North Carolina at Chapel Hill | Miyawaki K.,Shanghai Center for Plant Stress Biology | And 6 more authors.
Plant Journal | Year: 2015

Summary Auxin produced by an active primary shoot apex is transported down the main stem and inhibits the growth of the axillary buds below it, contributing to apical dominance. Here we use Arabidopsis thaliana cytokinin (CK) biosynthetic and signalling mutants to probe the role of CK in this process. It is well established that bud outgrowth is promoted by CK, and that CK synthesis is inhibited by auxin, leading to the hypothesis that release from apical dominance relies on an increased supply of CK to buds. Our data confirm that decapitation induces the expression of at least one ISOPENTENYLTRANSFERASE (IPT) CK biosynthetic gene in the stem. We further show that transcript abundance of a clade of the CK-responsive type-A Arabidopsis response regulator (ARR) genes increases in buds following CK supply, and that, contrary to their typical action as inhibitors of CK signalling, these genes are required for CK-mediated bud activation. However, analysis of the relevant arr and ipt multiple mutants demonstrates that defects in bud CK response do not affect auxin-mediated bud inhibition, and increased IPT transcript levels are not needed for bud release following decapitation. Instead, our data suggest that CK acts to overcome auxin-mediated bud inhibition, allowing buds to escape apical dominance under favourable conditions, such as high nitrate availability. Significance Statement It has been proposed that the release of buds from auxin-mediated apical dominance following decapitation requires increased cytokinin biosynthesis and consequent increases in cytokinin supply to buds. Here we show that in Arabidopsis, increases in cytokinin appear to be unnecessary for the release of buds from apical dominance, but rather allow buds to escape the inhibitory effect of apical auxin, thereby promoting bud activation in favourable growth conditions. © 2015 The Authors. Source

Miyawaki K.,University of California at Riverside | Miyawaki K.,Shanghai Center for Plant Stress Biology | Tabata R.,Kumamoto University | Tabata R.,Japan National Institute for Basic Biology | Sawa S.,Kumamoto University
Current Opinion in Plant Biology | Year: 2013

Small polypeptides are widely used as signaling molecules in cell-to-cell communication in animals and plants. The CLAVATA3/EMBRYO SURROUNDING REGION-RELATED (CLE) gene family is composed of numerous genes that contain conserved CLE domains in various plant species and plant-parasitic nematodes. Here, we review recent progress in our understanding of CLE signaling during stem cell maintenance in Arabidopsis and grasses. We also summarize the roles of CLE signaling in the legume-Rhizobium symbiosis and infection by plant-parasitic nematodes. CLE signaling is important for diverse aspects of cell-to-cell signaling and long-distance communication, which are critical for survival, and the basic components of the CLE signaling pathway are evolutionarily conserved in both plants and animals. © 2013 . Source

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