The pattern of plant annexin gene expression

Identification of differentially expressed genes in pistils from self-incompatible Citrus reticulata by suppression subtractive hybridization

Self-incompatibility (SI) is one important factor that can result in Citrus seedlessness. However, the molecular mechanism of SI in Citrus is not clear yet. To isolate the pistil's SI-related genes, a suppression subtractive hybridization library was constructed using mature pistils of 'Wuzishatangju' mandarin (SI) as the tester and mature pistils of 'Shatangju' mandarin (self-compatibility, SC) as the driver. 229 differentially expressed cDNA clones from 967 positive clones were sequenced and identified. Differentially expressed ESTs are possibly involved in the SI reaction of 'Wuzishatangju' through a regulating signaling pathway, serine/threonine phosphatase activity, receptor kinase, embryonic development, gibberellin stimulus, or transcription. 11 out of 36 SI candidate genes displayed different expression patterns in various tissues and stages after self- and cross-pollination of 'Wuzishatangju'. The expression of CaBP (WY65), a senescence-protease (WY372), an unknown gene (WY283), and a WRKY (WY17) were up-regulated in the styles of 'Wuzishatangju' while higher expression of WY190 was observed in styles of 'Shatangju'. Highest expression levels of WY65, WY372, an annexin (WY598), the zinc-finger protein (WY376), a C2-protein (WY291), and an unknown gene (WY318) were detected in styles at 3 days after self-pollination of 'Wuzishatangju' while lowest levels were observed in styles at 3 days after cross-pollination of 'Wuzishatangju' × 'Shatangju'. The potential involvement of these genes in the SI reaction is discussed.

Identification and characterization of annexin gene family in rice

Plant annexins are Ca(2+)-dependent phospholipid-binding proteins and are encoded by multigene families. They are implicated in the regulation of plant development as well as protection from drought and other stresses. They are well characterized in Arabidopsis, however no such characterization of rice annexin gene family has been reported thus far. With the availability of the rice genome sequence information, we have identified ten members of the rice annexin gene family. At the protein level, they share 16-64% identity with predicted molecular masses ranging from 32 to 40 kDa. Phylogenetic analysis of rice annexins together with annexins from other monocots led to their classification into five different orthologous groups and share similar motif patterns in their protein sequences. Expression analysis by real-time RT-PCR revealed differential temporal and spatial regulation of these genes. The rice annexin genes are also found to be regulated in seedling stage by various abiotic stressors including salinity, drought, heat and cold. Additionally, in silico analysis of the putative upstream sequences was analyzed for the presence of stress-responsive cis-elements. These results provide a basis for further functional characterization of specific rice annexin genes at the tissue/developmental level and in response to abiotic stresses.

Genomic organization, phylogenetic comparison and expression profiles of annexin gene family in tomato (Solanum lycopersicum)

Annexins have been suggested to play pivotal roles in stress resistance and plant development. However, related studies on fruit-bearing plants, especially on fruit development, are very limited. In the present study, we provide a comprehensive overview of the annexin family in tomato, describing the gene structure, promoter cis-regulatory elements, organ expression profile, and gene expression patterns under hormone and stress treatments. Bioinformatic analysis revealed that the nine tomato annexins were structurally different from their animal counterparts, but highly conserved annexin domains were still found in most of them. Cis-regulatory element prediction showed that there were important elements in the 2kb upstream promoter regions, including stress- and hormone-responsive-related elements. The expression patterns of these genes were investigated, and the results revealed that they were regulated under developmental processes and environmental stimuli. Among them, AnnSl1.1 and AnnSl2 were highly expressed in most of the tested organs. Genes preferentially or specifically expressed in organs, such as stigma or ovary (AnnSl6), stamen (AnnSl8), and fruit pericarp (AnnSl1.2 and AnnSl9), were identified. Some annexin genes were induced by plant hormones including abscisic acid (AnnSl3, AnnSl6, AnnSl8, and AnnSl9) and gibberellic acid (AnnSl1.1, AnnSl1.2, AnnSl4, and AnnSl7). Most of these annexin genes were induced by salt, drought, wounding, and heat or cold stresses. The present study provides significant information for understanding the diverse roles of annexins in tomato growth and development.

Molecular cloning and characterization of five annexin genes from Indian mustard (Brassica juncea L. Czern and Coss)

Plant annexins constitute a multigene family having suggested roles in a variety of cellular processes including stress responses. We have isolated and characterized five different cDNAs of mustard, Brassica juncea (AnnBj1, AnnBj2, AnnBj3, AnnBj6 and AnnBj7) encoding annexin proteins using a RT-PCR/RACE-PCR based strategy. The predicted molecular masses of these annexins are approximately 36.0 kDa with acidic pIs. At the amino acid level, they share high sequence similarity with each other and with annexins from higher plants. Phylogenetic analysis revealed their evolutionary relationship with corresponding orthologous sequences in Arabidopsis and deduced proteins in various plant species. Expression analysis by semi-quantitative RT-PCR revealed that these genes are differentially expressed in various tissues. The expression patterns of these genes also showed regulation by various stress conditions such as exposure to signaling molecules, salinity and oxidative stress and wounding. Additionally, the in silico promoter analysis (of AnnBj1, AnnBj2 and AnnBj3) showed the presence of different cis-responsive elements that could respond to various stress conditions. These results indicate that AnnBj genes may play important roles in adaptation of plants to various environmental stresses.

Identification of the first Oomycete annexin as a (1→3)-β-d-glucan synthase activator

(1-->3)-beta-D-Glucans are major components of the cell walls of Oomycetes and as such they play an essential role in the morphogenesis and growth of these microorganisms. Despite the biological importance of (1-->3)-beta-D-glucans, their mechanisms of biosynthesis are poorly understood. Previous studies on (1-->3)-beta-D-glucan synthases from Saprolegnia monoica have shown that three protein bands of an apparent molecular weight of 34, 48 and 50 kDa co-purify with enzyme activity. However, none of the corresponding proteins have been identified. Here we have identified, purified, sequenced and characterized a protein from the 34 kDa band and clearly shown that it has all the biochemical properties of proteins from the annexin family. In addition, we have unequivocally demonstrated that the purified protein is an activator of (1-->3)-beta-D-glucan synthase. This represents a new type of function for proteins belonging to the annexin family. Two other proteins from the 48 and 50 kDa bands were identified as ATP synthase subunits, which most likely arise from contaminations by mitochondria during membrane preparation. The results, which are discussed in relation with the possible regulation mechanisms of (1-->3)-beta-D-glucan synthases, represent a first step towards a better understanding of cell wall polysaccharide biosynthesis in Oomycetes.

A cellular hypothesis for the induction of blossom-end rot in tomato fruit

BACKGROUND

The incidence of blossom-end rot (BER) is generally associated with a calcium (Ca) deficiency in the distal portion of tomato fruits. The visible symptom is a necrotic lesion, which is presumed to be a consequence of cell death and the subsequent leakage of solutes into the extracellular space. Environmental factors that affect either fruit cell expansion or Ca delivery to the distal portion of the fruit influence the occurrence of BER. However, since no absolute, critical fruit Ca concentration for the occurrence of BER has been identified, it is now important to define the role of Ca in fruit cell physiology and to seek the cause of BER at the cellular level.

HYPOTHESIS

Here, it is suggested that BER is initiated by a cellular dysfunction in the distal portion of a young fruit during rapid cell expansion. It is proposed that insufficient Ca(2+) is available for critical apoplastic and cytoplasmic functions when the cellular Ca demand imposed by vacuolation exceeds the Ca delivery to an expanding cell. A local Ca deficiency, therefore, may result in aberrant intracellular Ca(2+) signals, a weakening of cell walls and a loss of cellular integrity. Ultimately it may lead to cell death and the visible symptoms of BER. Several experimental strategies are suggested to confirm the occurrence of aberrant Ca(2+) concentrations in cells contributing to BER.

PERSPECTIVE

Many genetic and genomic resources are becoming available for tomato. Ultimately, these will allow genes affecting the occurrence of BER to be identified. Such knowledge will inform breeding strategies to eliminate BER. In the meanwhile, increasing the apoplastic Ca concentration in susceptible fruit tissue should provide a simple and reliable, practical solution for the prevention of BER in tomatoes. It is suggested that current horticultural practices, such as the manipulation of the mineral composition of the feed or the growth environment, are not completely effective in reducing BER because they affect apoplastic Ca concentration in fruit tissue indirectly. Therefore, spraying Ca directly onto young fruits is recommended for the prevention of BER.

SNAMA, a novel protein with a DWNN domain and a RING finger-like motif: a possible role in apoptosis

We have characterized SNAMA a hitherto uncharacterized Drosophila protein that appears to play a role in apoptosis. SNAMA (something that sticks like glue) is a 1231 amino acid protein with a conserved 76 residue N-terminal domain called Domain With No Name (DWNN). The DWNN domain was first identified in cytotoxic T Cell-resistant CHO cells using promoter trap mutagenesis to screen for genes involved in apoptosis. Subsequently, this domain was identified in other eukaryotic organisms including animals and plants. The SNAMA transcript is abundant early in embryogenesis but reduced in older embryos and in adult males and females. Human and mouse homologues of SNAMA are known to bind to p53 and to the retinoblastoma protein (Rb) suggesting a role in transcriptional regulation and cell cycle control. We took advantage of a P-element insertion line in which the P-element is inserted in the first intron, to investigate the biological function of the gene. These mutants are lethal when homozygous. Apoptosis appears early during embryogenesis and is observed virtually throughout the gastrula. The DWNN domain has a ubiquitin-like fold and may interact with a subset of cellular proteins. There is also a conserved RING finger-like motif along the sequence of SNAMA following a C2HC zinc finger.

Targeted proteomics to identify cadmium-induced protein modifications in Glomus mosseae-inoculated pea roots

•   Arbuscular mycorrhiza (AM) can increase plant tolerance to heavy metals. A targeted proteomic approach was used to determine the putative identity of some of the proteins induced/modulated by cadmium (Cd) and to analyse the impact of the mycorrhizal process. •   The effect of Cd (100 mg Cd kg^-1  substrate) applied either at planting or 15 d later on two pea (Pisum sativum) genotypes, differing in sensitivity to Cd inoculated or not with the AM fungus Glomus mosseae, was studied at three levels: plant biomass production, development of G. mosseae and root differential protein display with one- and two-dimensional gel electrophoresis (1-DE and 2-DE) analyses. •   Cd-induced growth inhibition was significantly alleviated by mycorrhiza in the Cd-sensitive genotype. The AM symbiosis modulated the expression of several proteins, identified by liquid chromatography-tandem mass spectrometry, newly induced and upregulated or downregulated by Cd. •   The protective effect of AM symbiosis towards Cd stress was observed in the Cd-sensitive genotype. Our results demonstrate the usefulness of proteomics to better understand the possible role of AM symbiosis in detoxification/response mechanisms towards Cd in pea plants.

Genes for calcium-permeable channels in the plasma membrane of plant root cells

In plant cells, Ca(2+) is required for both structural and biophysical roles. In addition, changes in cytosolic Ca(2+) concentration ([Ca(2+)](cyt)) orchestrate responses to developmental and environmental signals. In many instances, [Ca(2+)](cyt) is increased by Ca(2+) influx across the plasma membrane through ion channels. Although the electrophysiological and biochemical characteristics of Ca(2+)-permeable channels in the plasma membrane of plant cells are well known, genes encoding putative Ca(2+)-permeable channels have only recently been identified. By comparing the tissue expression patterns and electrophysiology of Ca(2+)-permeable channels in the plasma membrane of root cells with those of genes encoding candidate plasma membrane Ca(2+) channels, the genetic counterparts of specific Ca(2+)-permeable channels can be deduced. Sequence homologies and the physiology of transgenic antisense plants suggest that the Arabidopsis AtTPC1 gene encodes a depolarisation-activated Ca(2+) channel. Members of the annexin gene family are likely to encode hyperpolarisation-activated Ca(2+) channels, based on their corresponding occurrence in secretory or elongating root cells, their inhibition by La(3+) and nifedipine, and their increased activity as [Ca(2+)](cyt) is raised. Based on their electrophysiology and tissue expression patterns, AtSKOR encodes a depolarisation-activated outward-rectifying (Ca(2+)-permeable) K(+) channel (KORC) in stelar cells and AtGORK is likely to encode a KORC in the plasma membrane of other Arabidopsis root cells. Two candidate gene families, of cyclic-nucleotide gated channels (CNGC) and ionotropic glutamate receptor (GLR) homologues, are proposed as the genetic correlates of voltage-independent cation (VIC) channels.

Plant annexins form calcium-independent oligomers in solution

The oligomeric state in solution of four plant annexins, namely Anx23(Ca38), Anx24(Ca32), Anx(Gh1), and Anx(Gh2), was characterized by sedimentation equilibrium analysis and gel filtration. All proteins were expressed and purified as amino-terminal His(n) fusions. Sequencing of the Anx(Gh1) construct revealed distinct differences with the published sequence. Sedimentation equilibrium analysis of Anx23(Ca38), Anx24(Ca32), and Anx(Gh1) suggests monomer-trimer equilibria for each protein with association constants in the range of 0.9 x 10(10)-1.7 x 10(11) M(-2). All four proteins were subjected to analytical gel filtration under different buffer conditions. Observations from this experiment series agree quantitatively with the ultracentrifugation results, and strongly suggest calcium independence of the annexin oligomerization behavior; moreover, binding of calcium ions to the proteins seems to require disassembly of the oligomers. Anx(Gh2) showed a different elution profile than the other plant annexins; while having only a very small trimer content, this annexin seems to exist in a monomer-dimer equilibrium in solution.

Sulfolipid is a potential candidate for annexin binding to the outer surface of chloroplast

Using a subcellular-specific proteomic approach, we have identified by protein microsequencing, a putative 35-kDa annexin from among the chloroplast envelope polypeptides. To confirm this identification, we demonstrate that (a) a 35-kDa protein, identified as annexin by antibody cross-reactivity, co-purifies with Percoll-purified chloroplasts and their envelope membranes when extracted in the presence of Ca(2+) and (b) the native spinach annexin protein binds to chloroplast-specific lipids in a Ca(2+)-dependent manner. The binding of the spinach annexin to these glycerolipids occurs at similar Ca(2+) concentrations as those, which promote the interaction of annexins to phospholipids in other membranes. Among chloroplast glycerolipids known to be accessible on the cytosolic face (outer leaflet) of the outer envelope membrane, sulfolipid, and probably phosphatidylinositol, would be the sole candidates for a putative Ca(2+)-dependent interaction of annexin with the chloroplast surface.

Regulation of biosynthesis and cellular localization of Sp32 annexins in tobacco BY2 cells

Annexins interact in a calcium-dependent manner with membrane phospholipids. Although their exact function is not known, annexins have been proposed to be involved in a variety of cellular processes. To determine whether plant annexins are implicated in cell division, we have isolated cDNAs encoding annexin from TBY2 cells. Based on sequence analysis, these cDNAs fall into two families, differing mainly by deletions or insertions in their 5'- and 3'-untranslated regions. The two annexins Ntp32.1 and Ntp32.2 encoded by these cDNAs are homologous to p32 from bell pepper (Cap32.1): we propose that these Solanaceae annexins constitute a distinct type which we call Sp32 annexins. There are two genes (Ntan.1 and Ntan.2) derived from the separate progenitor species of Nicotiana tabacum and analysis of Southern blots is consistent with the presence of these two genes. We show that Sp32 transcript amounts are developmentally modulated in tobacco plants: RNA levels are highest in growing and dividing tissues. Sp32 annexin gene expression is also regulated in TBY2 cultured cells: transcripts and proteins are detected only in exponentially growing cells. In synchronized TBY2 cells, Sp32 annexin transcripts are expressed at the G2/M transition, in the M phase and at the G1/S transition. These results are the first evidence that the expression of plant annexins is modulated during the cell cycle. The Sp32 annexin proteins accumulate during the cell cycle and peak at the end of mitosis. Immunolocalization shows that the majority of Sp32 annexins is present in intercellular junctions, forming a ring structure under the plasma membrane. Since annexins are known to bind secretory vesicles during exocytosis, their localization at cell junctions suggests that annexins could be involved in cell wall maturation.

Regulation of biosynthesis and cellular localization of Sp32 annexins in tobacco BY2 cells

Annexins interact in a calcium-dependent manner with membrane phospholipids. Although their exact function is not known, annexins have been proposed to be involved in a variety of cellular processes. To determine whether plant annexins are implicated in cell division, we have isolated cDNAs encoding annexin from TBY2 cells. Based on sequence analysis, these cDNAs fall into two families, differing mainly by deletions or insertions in their 5'- and 3'-untranslated regions. The two annexins Ntp32.1 and Ntp32.2 encoded by these cDNAs are homologous to p32 from bell pepper (Cap32.1): we propose that these Solanaceae annexins constitute a distinct type which we call Sp32 annexins. There are two genes (Ntan.1 and Ntan.2) derived from the separate progenitor species of Nicotiana tabacum and analysis of Southern blots is consistent with the presence of these two genes. We show that Sp32 transcript amounts are developmentally modulated in tobacco plants: RNA levels are highest in growing and dividing tissues. Sp32 annexin gene expression is also regulated in TBY2 cultured cells: transcripts and proteins are detected only in exponentially growing cells. In synchronized TBY2 cells, Sp32 annexin transcripts are expressed at the G2/M transition, in the M phase and at the G1/S transition. These results are the first evidence that the expression of plant annexins is modulated during the cell cycle. The Sp32 annexin proteins accumulate during the cell cycle and peak at the end of mitosis. Immunolocalization shows that the majority of Sp32 annexins is present in intercellular junctions, forming a ring structure under the plasma membrane. Since annexins are known to bind secretory vesicles during exocytosis, their localization at cell junctions suggests that annexins could be involved in cell wall maturation.

The growing cell plate of higher plants is a site of both actin assembly and vinculin-like antigen recruitment

Compelling evidence supports the idea that actin filaments play an active role in the cytokinetic process of higher plant cells. However, the mechanisms that control the growth of the cell plate and its stabilization remain so far unknown. We show that a novel population of short actin filaments continuously assembles in the phragmoplast at the growing cell plate. Microinjection of rhodamine-phalloidin during these final stages of telophase revealed the dynamic assembly and organization of these actin filaments during vesicle fusion. Comparable data were obtained in endosperm syncytia during the development of the cell plate between non sister nuclei, i.e. independently of the formation of the mitotic phragmoplast. Concomitantly, plant polypeptides sharing epitopes with human vinculin are revealed within the forming cell plate, suggesting their recruitment during cytokinesis-associated actin assembly. These vinculin-like antigens may participate in membrane/F-actin anchorage protein complexes. Our data, in addition to the identification of plant integrin homologues reported by several authors, suggest the existence of a cell wall/extracellular matrix/plasma membrane/actin cytoskeleton continuum. Such an architecture may control cell-cell interactions during cell plate formation and may contribute to the establishment of polarity in higher plants.

Characterization and gene expression of an annexin during fruit development in Capsicum annuum

Several lines of evidence indicate that annexins, as calcium-dependent phospholipid-binding proteins, are involved in a variety of plant cellular processes. We were interested in determining if annexins are implicated in the highly regulated fruit development of bell pepper. By differential screening of several cDNA libraries, we isolated a full-length cDNA of 1180 bp encoding an annexin. Northern blot analyses show a differential expression pattern of the transcripts during the early stages of development and during ripening. Immunoblots using antiserum raised against p33/p35 from maize reveal that cross-reactive polypeptides of about 30 kDa are present at each stage of fruit development in bell pepper. We partially purified the annexins from seedlings and green fruits. At least one annexin of 32 kDa is present in these plant tissues.

Tomato annexins p34 and p35 bind to F-actin and display nucleotide phosphodiesterase activity inhibited by phospholipid binding

Annexins are a family of proteins found in a range of eukaryotic cell types. They share a characteristic amino acid sequence and a Ca(2+)-dependent affinity for specific phospholipids. In plants, proteins with common properties and significant homology with annexins have been identified in a number of species and implicated in diverse cellular functions known to be modulated by Ca2+. This study describes several novel biochemical properties of the tomato annexins p34 and p35 that are relevant to our understanding of their functions in the plant. First, the annexins were found to bind to actin in a calcium- and pH-dependent interaction that was specific for F-actin and not G-actin. Second, an enzyme activity defined as a nucleotide phosphodiesterase activity was found associated with the purified annexin preparation. Selective immunoprecipitation of p34 and p35 strongly suggests that the enzyme activity is a property of the annexins and constitutes 60% of the total soluble activity found in root extracts capable of hydrolyzing free ATP. The substrate specificity of the enzyme within in vitro assays is broad. ATP is the preferred substrate, but nearly identical rates of hydrolysis of GTP and substantial hydrolysis of other nucleotide tri- and diphosphates are observed. The enzyme activity was found to be a property of both p34 and p35, although the specific activity was routinely higher for p34. Third, the enzyme activity of the annexins was not affected by F-actin binding but could be abolished by the specific Ca(2+)-dependent interaction of the annexins with phospholipids. Our results showed that p34 and p35 account for substantial enzyme activity in tomato root cells. This activity was exhibited when the proteins were either in soluble form or attached to actin filaments. Enzyme activity was not exhibited when the annexins were bound to phospholipids. These properties suggest a role for the proteins in mediating Ca(2+)-dependent events involving interactions of the cytoskeleton and cellular membranes.

Identification of mRNAs with enhanced expression in ripening strawberry fruit using polymerase chain reaction differential display

Fruit ripening is a complex developmental process that involves specific changes in gene expression and cellular metabolism. In climateric fruits these events are coordinated by the gaseous hormone ethylene, which is synthesized autocatalytically in the early stages of ripening. Nonclimacteric fruits do not synthesize or respond to ethylene in this manner, yet undergo many of the same physiological and biochemical changes associated with the production of a ripe fruit. To gain insight into the molecular determinants associated with nonclimacteric fruit ripening, we examined mRNA populations in ripening strawberry fruit using polymerase chain reaction (PCR) differential display. Five mRNAs with ripening-enhanced expression were identified using this approach. Three of the mRNAs appear to be fruit-specific, with little or no expression detected in vegetative tissues. Sequence analysis of cDNA clones revealed positive identities for three of the five mRNAs based on homology to known proteins. These results indicate that the differential display technique can be a useful tool to study fruit ripening and other developmental processes in plants at the RNA level.

Cotton fiber annexins: a potential role in the regulation of callose synthase

Cotton fibers contain a characteristic set of proteins which interact with plasma membranes in a Ca(2+)-dependent manner. The association of these proteins with the membrane is correlated with a reduced level of UDP-glucose: (1-->3)-beta-glucan (callose) synthase activity. Analysis of the proteins released from membranes by EDTA treatment shows that the most abundant proteins comprise a family of at least three polypeptides (p34) which resemble annexins. This resemblance includes similarity in size (about 34 kDa), sequence homology, Ca(2+)-dependent precipitation or interaction with the plasma membrane, and ability to serve as a substrate for phosphorylation by endogenous protein kinase(s) which also bind to the membranes in a Ca(2+)-dependent manner. A purified fraction of these annexins binds to, and inhibits, the activity of a partially purified cotton fiber callose synthase. These findings suggest that one possible function of annexin(s) in plants is to modulate the activity and/or localization of callose synthase.