Regulation of the polarity of protein trafficking by phosphorylation

The asymmetry of environmental stimuli and the execution of developmental programs at the organism level require a corresponding polarity at the cellular level, in both unicellular and multicellular organisms. In plants, cell polarity is important in major developmental processes such as cell division, cell enlargement, cell morphogenesis, embryogenesis, axis formation, organ development, and defense. One of the most important factors controlling cell polarity is the asymmetric distribution of polarity determinants. In particular, phosphorylation is implicated in the polar distribution of the determinant protein factors, a mechanism conserved in both prokaryotes and eukaryotes. In plants, formation of local gradients of auxin, the morphogenic hormone, is critical for plant developmental processes exhibiting polarity. The auxin efflux carriers PIN-FORMEDs (PINs) localize asymmetrically in the plasma membrane and cause the formation of local auxin gradients throughout the plant. The asymmetry of PIN distribution in the plasma membrane is determined by phosphorylationmediated polar trafficking of PIN proteins. This review discusses recent studies on the role of phosphorylation in polar PIN trafficking.     

The phosphorylation code is implicated in cell type-specific trafficking of PIN-FORMEDs

The subcellular polarity of PIN-FORMEDs (PINs) is critical for directional cell-to-cell transport of auxin. Phosphorylation of PIN proteins plays an important role in generating and maintaining specific PIN polarity. In a recent study, we have shown that phosphorylation in certain conserved residues of the PIN3 hydrophilic loop (HL) modulates its subcellular localization and polarity in a cell type-specific manner in different root tissues. Here, we additionally show that the phosphorylation code of PIN3-HL is operational for the determination of PIN3 polarity in the Arabidopsis guard cell and is deciphered in a differential way even in a single tobacco cell for the intracellular trafficking of PIN3. On the other hand, PIN3 localization often remained unaltered in certain cell types irrespective of its phosphorylation status. These findings, together with previous reports, indicate that the phosphorylation code of the PIN-HL along with cell type-specific factors, kinases, and developmental/environmental cues is instrumental for the PIN trafficking to different subcellular compartments as well as different plasma membrane domains.     

The march of the PINs: developmental plasticity by dynamic polar targeting in plant cells

Development of plants and their adaptive capacity towards ever‐changing environmental conditions largely depend on the spatial distribution of the plant hormone auxin. At the cellular level, various internal and external signals are translated into specific changes in the polar, subcellular localization of auxin transporters from the PIN family thereby directing and redirecting the intercellular fluxes of auxin. The current model of polar targeting of PIN proteins towards different plasma membrane domains encompasses apolar secretion of newly synthesized PINs followed by endocytosis and recycling back to the plasma membrane in a polarized manner. In this review, we follow the subcellular march of the PINs and highlight the cellular and molecular mechanisms behind polar foraging and subcellular trafficking pathways. Also, the entry points for different signals and regulations including by auxin itself will be discussed within the context of morphological and developmental consequences of polar targeting and subcellular trafficking.     

生长素输出载体PIN家族研究进展

生长素极性运输调控植物的生长发育。生长素极性运输主要依赖3类转运蛋白: AUX/LAX、PIN和ABCB蛋白家族。生长素在细胞间流动的方向与PIN蛋白在细胞上的极性定位密切相关。PIN蛋白由1个中心亲水环和2个由中心亲水环隔开的疏水区组成。中心亲水环上含多个磷酸化位点,其为一些蛋白激酶的靶点。PIN蛋白受多方面调控,包...     

Polar auxin transport – old questions and new concepts?

Polar auxin transport controls multiple aspects of plant development including differential growth, embryo and root patterning and vascular tissue differentiation. Identification of proteins involved in this process and availability of new tools enabling `visualization' of auxin and auxin routes in planta largely contributed to the significant progress that has recently been made. New data support classical concepts, but several recent findings are likely to challenge our view on the mechanism of auxin transport. The aim of this review is to provide a comprehensive overview of the polar auxin transport field. It starts with classical models resulting from physiological studies, describes the genetic contributions and discusses the molecular basis of auxin influx and efflux. Finally, selected questions are presented in the context of developmental biology, integrating available data from different fields.     

ABI4调控侧根发育研究(综述)

生长素是调控植物侧根发育的关键植物激素,生长素运输载体PIN蛋白介导其极性分布。ABI4抑制生长素极性运输蛋白基因PIN1的表达,影响生长素的极性运输,抑制侧根形成。本文概述ABI4转录因子调控侧根发育的研究进展。     

Shedding light on auxin movement: Light-regulation of polar auxin transport in the photocontrol of plant development

By being sessile, plants have evolved a remarkable capacity to perceive and respond to changes in environmental conditions throughout their life cycle. Light represents probably the most important environmental factor that impinge on plant development because, other than supplying the energy source for photosynthesis, it also provides seasonal and positional information that are essential for the plant survival and fitness. Changes in the light environment can dramatically alter plant morphogenesis, especially during the early phases of plant life, and a compelling amount of evidence indicates that light-mediated changes in auxin homeostasis are central in these processes. Auxin exerts its morphogenetic action through instructive hormone gradients that drive developmental programs of plants. Such gradients are formed and maintained via an accurate control on directional auxin transport. This review summarizes the recent advances in understanding the influence of the light environment on polar auxin transport.     

A Pin gene families encoding components of auxin efflux carriers in Brassica juncea

Based on the sequence information of Arabidopsis PIN1, two cDNAs encoding PIN homologues fromBrassica juncea, Bjpin2 and Bjpin3, were isolated through cDNA library screening. Bjpin2 and Bjpin3encoded proteins containing 640 and 635 amino acid residues, respectively, which shared 97.5% identities witheach other and were highly homologous to Arabidopsis PIN1, PIN2 and other putative PIN proteins. BjPIN2and BjPIN3 had similar structures as AtPIN proteins. Northern blot analysis indicated that Bjpin2 wasexpressed in stem, leaf and floral tissues, while Bjpin3 was expressed predominantly in stem and hypocotyls.Two promoter fragments of pin genes, Bjpin-X and Bjpin-Z, were isolated by ‘genome walking‘ techniqueusing primers at 5‘-end of pin cDNA. Promoter-gus fusion studies revealed the GUS activities driven byBjpin-X were at internal side of xylem and petal; while those driven by Bjpin-Z were detected at leaf vein,epidermal cell and cortex of stem, vascular tissues and anther. Results of the pin genes with differentexpression patterns in B. juncea suggested the presence of a gene family.     

A Pin gene families encoding components of auxin efflux carriers in Brassica juncea

Based on the sequence information of Arabidopsis PIN1, two cDNAs encoding PIN homologues from Brassica juncea, Bjpin2 and Bjpin3, were isolated through cDNA library screening. Bjpin2 and Bjpin3 encoded proteins containing 640 and 635 amino acid residues, respectively, which shared 97.5% identities with each other and were highly homologous to Arabidopsis PIN1, PIN2 and other putative PIN proteins. BJPIN2 and BjPIN3 had similar structures as AtPIN proteins. Northern blot analysis indicated that Bjpin2 was expressed in stem, leaf and floral tissues, while Bjpin3 was expressed predominantly in stem and hypocotyls. Two promoter fragments of pin genes, Bjpin-X and Bjpin-Z, were isolated by 'genome walking' technique using primers at 5'-end of pin cDNA. Promoter-gus fusion studies revealed the GUS activities driven by Bjpin-X were at internal side of xylem and petal; while those driven by Bjpin-Z were detected at leaf vein, epidermal cell and cortex of stem, vascular tissues and anther. Results of the pin gene     

类黄酮调节生长素的极性运输(综述)

生长素在植物体内是通过极性运输方式输送的,这个运输过程是一个严格调控的过程.目前对其调控机理尚不了解.植物体内广泛存在的类黄酮类物质影响生长素运输,对生长素运输起负调控作用.