Ubiquitination regulates the plasma membrane expression of renal UT-A urea transporters

The renal UT-A urea transporters UT-A1, UT-A2, and UT-A3 are known to play an important role in the urinary concentrating mechanism. The control of the cellular localization of UT-A transporters is therefore vital to overall renal function. In the present study, we have investigated the effect of ubiquitination on UT-A plasma membrane expression in Madin-Darby canine kidney (MDCK) cell lines expressing each of the three renal UT-A transporters. Inhibition of the ubiquitin-proteasome pathway caused an increase in basal transepithelial urea flux across MDCK-rat (r)UT-A1 and MDCK-mouse (m)UT-A2 monolayers (P < 0.01, n = 3, ANOVA) and also increased dimethyl urea-sensitive, arginine vasopressin-stimulated urea flux (P < 0.05, n = 3, ANOVA). Inhibition of the ubiquitin-proteasome pathway also increased basolateral urea flux in MDCK-mUT-A3 monolayers (P < 0.01, n = 4, ANOVA) in a concentration-dependent manner. These increases in urea flux corresponded to a significant increase in UT-A transporter expression in the plasma membrane (P < 0.05, n = 3, ANOVA). Further analysis of the MDCK-mUT-A3 cell line confirmed that vasopressin specifically increased UT-A3 expression in the plasma membrane (P < 0.05, n = 3, ANOVA). However, preliminary data suggested that vasopressin produces this effect through an alternative route to that of the ubiquitin-proteasome pathway. In conclusion, our study suggests that ubiquitination regulates the plasma membrane expression of all three major UT-A urea transporters, but that this is not the mechanism primarily used by vasopressin to produce its physiological effects. ubiquitin-proteasome pathway; urea transport; membrane localization     

Cyclic dinucleotides at the forefront of innate immunity

Cyclic dinucleotides (CDNs) have emerged as ubiquitous signaling molecules in all domains of life. In eukaryotes, CDN signaling systems are evolutionarily ancient and have developed to sense and respond to pathogen infection. On the other hand, dysregulation of these pathways has been implicated in the pathogenesis of autoimmune diseases. Thus, CDNs have garnered major interest over recent years for their ability to elicit potent immune responses in the eukaryotic host. Similarly, ancestral CDN-based signaling systems also appear to confer immunological protection against infection in prokaryotes. Therefore, a better understanding of the host processes regulated by CDNs will be of tremendous value in many areas of research. Here, we aim to review the latest discoveries and recent trends in CDN research with a particular focus on the molecular mechanisms by which these small molecules mediate innate immunity.     

Hemiascomycetous yeasts at the forefront of comparative genomics

With more than a dozen species fully sequenced, as many as this partially sequenced, and more in development, yeasts are now used to explore the frontlines of comparative genomics of eukaryotes. Innovative procedures have been developed to compare and annotate genomes at various evolutionary distances, to identify short cis-acting regulatory elements, to map duplications, or to align syntenic blocks. Human and plant pathogens, in addition to yeasts that show a variety of interesting physiological properties, are included in this multidimensional comparative survey, which encompasses a very broad evolutionary range. As major steps of the evolutionary history of hemiascomycetous genomes emerge, precise questions on the general mechanisms of their evolution can be addressed, using both experimental and in silico methods.     

Ubiquitination of pattern recognition receptors in plant innate immunity

Lacking an adaptive immune system, plants largely rely on plasma membrane‐resident pattern recognition receptors (PRRs) to sense pathogen invasion. The activation of PRRs leads to the profound immune responses that coordinately contribute to the restriction of pathogen multiplication. Protein post‐translational modifications dynamically shape the intensity and duration of the signalling pathways. In this review, we discuss the specific regulation of PRR activation and signalling by protein ubiquitination, endocytosis and degradation, with a particular focus on the bacterial flagellin receptor FLS2 (flagellin sensing 2) in Arabidopsis.     

Anion transporters in plant mitochondria

The swelling of potato (Solanum tuberosum L.) mitochondria in isosmotic ammonium salts of phosphate, chloride, malate, succinate, and citrate was investigated by measuring light scattering. Potato mitochondria swell spontaneously in ammonium phosphate, and this swelling can be inhibited in N-ethylmaleimide. They swell in ammonium malate or succinate only after the addition of inorganic phosphate and in ammonium citrate only after the addition of both phosphate and a dicarboxylic acid. Pentylmalonate inhibits swelling in ammonium citrate solutions by competing for dicarboxylate entry. The results indicate that potato mitochondria possess a phosphate-hydroxyl carrier, a dicarboxylate carrier, and a tricarboxylate carrier.     

植物硫转运蛋白研究进展

硫转运蛋白在植物对硫酸盐的吸收和转运中起着重要的作用。已经在拟南芥、大麦和小麦等植物中分离到了40多种硫转运蛋白基因。这些基因序列与其他种类生物的硫转运蛋白基因序列有着高度的保守性。利用CLUSTAL程序建立的系统进化树将植物硫转运蛋白划分为5个亚群。使用多种拓扑预测程序推测出不同植物硫转运蛋白的共同结构特点是均含有12个跨膜域。在柱花草和大麦中,硫转运蛋白基因表达调控包括植物体内硫水平的负调控和O—乙酰丝氨酸的正调控两种方式。对硫转运蛋白的组织定位和功能研究表明,高亲和硫转运蛋白主要定位于根部,在根系硫酸盐吸收中起重要作用。     

植物钾营养性状的遗传潜力v

钾是植物生长发育所必需的大量元素,是与氮、磷并列的植物营养的“三大要素”之一。不同植物种类或同种类植物的不同品种之间钾营养效率的差异非常显著,这为植物钾营养性状的遗传改良提供了科学依据     

Exposing the hidden half: root research at the forefront of science

Plant and Soil - Soil organic matter (SOM) supports multiple soil ecosystem functions, underpinned by processes such as C sequestration, N mineralization, aggregation, promotion of plant health and...     

Sugar transporters in plant biology.

Sugar transporters are key players in many fundamental processes in plant growth and development. Recent results have identified several new transporters that contribute to a wide array of physiological activities, and detailed molecular analysis has provided exciting insights into the structure and regulation of these essential membrane proteins.     

Molecular physiology of higher plant sucrose transporters

Sucrose is the primary product of photosynthetic CO(2) fixation that is used for the distribution of assimilated carbon within higher plants. Its partitioning from the site of synthesis to different sites of storage, conversion into other storage compounds or metabolic degradation involves various steps of cell-to-cell movement and transport. Many of these steps occur within symplastic domains, i.e. sucrose moves passively cell-to-cell through plasmodesmata. Some essential steps, however, occur between symplastically isolated cells or tissues. In these cases, sucrose is transiently released into the apoplast and its cell-to-cell transport depends on the activity of plasma membrane-localized, energy dependent, H(+)-symporting carrier proteins. This paper reviews the current knowledge of sucrose transporter physiology and molecular biology.     

The plant PDR family of ABC transporters

The plant pleiotropic drug resistance (PDR) family of ATP-binding cassette (ABC) transporters has been implicated in the transport of antifungal agents. In this paper, we provide an analysis of the entire family of PDR genes present in the Arabidopsis thaliana (L.) Heynh. genome. This analysis both resolves discrepancies in published inventories of plant ABC proteins and provides an expression analysis of all the annotated Arabidopsis PDR genes. The results indicate that the Arabidopsis genome contains 15 genes encoding PDR proteins and that these genes show a spectrum of specific expression patterns, both at the organ level and in response to various hormonal, environmental and chemical factors. These data provide a scaffold for the future molecular genetic analysis of this important family of ABC transporters. In addition, we demonstrate the usefulness of such data by using them to identify an Arabidopsis PDR protein that may play a role in the extrusion of the antifungal diterpene sclareol. Electronic Supplementary Material is available if you access this article at http://dx.doi.org/10.1007/s00425-002-0889-z. On that page (frame on the left side), a link takes you directly to the supplementary material.     

ABC transporters involved in the transport of plant secondary metabolites

Plants produce a large number of secondary metabolites, such as alkaloids, terpenoids, polyphenols, quinones and many further compounds having combined structures of those groups. Physiological roles of those metabolites for plants are still under investigation, but they play, at least in part, important functions as protectants for plant bodies against herbivores and pathogens, as well as from physical stresses like ultraviolet light and heat. In order to accomplish these functions, biosyntheses and accumulation of secondary metabolites are highly regulated in a temporal and spatial manner in plant organs, where they can appropriately accumulate. In this mini-review, I introduce the mechanism of accumulation and membrane transport of these metabolites, in particular, focusing on ATP-binding cassette transporters involved.     

Effects of wheat plant inoculation with cytokinin-producing microorganisms on plant growth at increasing level of mineral nutrition

Triticum durum Desf. plants were grown for 11 days in sand culture on nutrient solutions with optimum or lowered content of mineral nutrients. Thereafter, the level of mineral nutrition was increased in some portion of deficient plants. Two days before, plants were inoculated with cytokinin-producing microorganisms of the Bacillus genus. Nutrition deficiency resulted in a decrease in the rate of plant biomass accumulation, which was correlated with the level of active cytokinins in both roots and shoots. After improving the mineral nutrition of noninoculated plants, the rate of their biomass accumulation increased and, by the end of experiment, their shoot fresh weight was 1.5-fold higher than in deficient plants; however, it was still by 20% lower than in plants continuously growing at optimum mineral nutrition. Inoculation resulted in the considerable increase in the cytokinin content in shoots as compared with all other treatments. In this case, after the improvement of plant mineral nutrition, the rates of growth and relative biomass accumulation increased sharply; as a result, these plants had the highest dry and fresh weights. Thus, inoculation with cytokinin-producing bacteria was beneficial for plant growth after their transfer from deficient to sufficient mineral nutrition.     

Ubiquitination of p53 at multiple sites in the DNA-binding domain

The tumor suppressor p53 is negatively regulated by the ubiquitin ligase MDM2. The MDM2 recognition site is at the NH2-terminal region of p53, but the positions of the actual ubiquitination acceptor sites are less well defined. Lysine residues at the COOH-terminal region of p53 are implicated as sites for ubiquitination and other post-translational modifications. Unexpectedly, we found that substitution of the COOH-terminal lysine residues did not diminish MDM2-mediated ubiquitination. Ubiquitination was not abolished even after the entire COOH-terminal regulatory region was removed. Using a method involving in vitro proteolytic cleavage at specific sites after ubiquitination, we found that p53 was ubiquitinated at the NH2-terminal portion of the protein. The lysine residue within the transactivation domain is probably not essential for ubiquitination, as substitution with an arginine did not affect MDM2 binding or ubiquitination. In contrast, several conserved lysine residues in the DNA-binding domain are critical for p53 ubiquitination. Removal of the DNA-binding domain reduced ubiquitination and increased the stability of p53. These data provide evidence that in addition to the COOH-terminal residues, p53 may also be ubiquitinated at sites in the DNA-binding domain.