A mutual support mechanism through intercellular movement of CAPRICE and GLABRA3 can pattern the Arabidopsis root epidermis

The patterning of the Arabidopsis root epidermis depends on a genetic regulatory network that operates both within and between cells. Genetic studies have identified a number of key components of this network, but a clear picture of the functional logic of the network is lacking. Here, we integrate existing genetic and biochemical data in a mathematical model that allows us to explore both the sufficiency of known network interactions and the extent to which additional assumptions about the model can account for wild-type and mutant data. Our model shows that an existing hypothesis concerning the autoregulation of WEREWOLF does not account fully for the expression patterns of components of the network. We confirm the lack of WEREWOLF autoregulation experimentally in transgenic plants. Rather, our modelling suggests that patterning depends on the movement of the CAPRICE and GLABRA3 transcriptional regulators between epidermal cells. Our combined modelling and experimental studies show that WEREWOLF autoregulation does not contribute to the initial patterning of epidermal cell fates in the Arabidopsis seedling root. In contrast to a patterning mechanism relying on local activation, we propose a mechanism based on lateral inhibition with feedback. The active intercellular movements of proteins that are central to our model underlie a mechanism for pattern formation in planar groups of cells that is centred on the mutual support of two cell fates rather than on local activation and lateral inhibition.

A Cyclical Semicontinuous Process for Production of Human α1-Antitrypsin Using Metabolically Induced Plant Cell Suspension Cultures

Transgenic rice suspension cultures were utilized to produce a human therapeutic protein, recombinant alpha(1)-antitrypsin (rAAT), in a cyclical, semicontinuous operation. Recombinant protein production was induced by removing the carbon source from the cell culture medium. The transgenic rice cells secreted the rAAT into the medium, and therefore medium exchanges could be performed for consecutive growth and protein expression phases. The process consisted of three cycles over a 25-28 day period, with growth phases lasting 4-6 days each and protein expression phases lasting 2.5-5 days each. Biomass and sugar concentrations, oxygen uptake rate, cell viability, culture pH, total extracellular protein, and active rAAT were measured throughout the cyclical process. The data profiles were reproducible between separate cyclical runs where, following each induction period, cell growth and viability could be reestablished once sucrose was added back to the culture. Volumetric productivities ranged from 3 to 12 mg active rAAT/(L day) for individual cycles with overall volumetric productivities of 4.5 and 7.7 mg active rAAT/(L day).

A transient assay to evaluate the expression of polyhydroxybutyrate genes regulated by oil palm mesocarp-specific promoter

The promoter of the oil palm metallothionein-like gene (MT3-A) demonstrated mesocarp-specific activity in functional analysis using transient expression assay of reporter gene in bombarded oil palm tissue slices. In order to investigate the tissue-specific expression of polyhydroxybutyrate (PHB) biosynthetic pathway genes, a multi-gene construct carrying PHB genes fused to the oil palm MT3-A promoter was co-transferred with a construct carrying GFP reporter gene using microprojectile bombardment targeting the mesocarp and leaf tissues of the oil palm. Transcriptional analysis using RT-PCR revealed successful transcription of all the three phbA, phbB, and phbC genes in transiently transformed mesocarp but not in transiently transformed leaf tissues. Furthermore, all the three expected sizes of PHB-encoded protein products were only detected in transiently transformed mesocarp tissues on a silver stained polyacrylamide gel. Western blot analysis using polyclonal antibody specific for phbB product confirmed successful translation of phbB mRNA transcript into protein product. This study provided valuable information, supporting the future engineering of PHB-producing transgenic palms.

[Induction, regeneration, and biolistic sensitivity of different genotypes of common wheat (Triticum aestivum L.)]

The induction, regeneration, and biolistic sensitivities of different genotypes of common wheat (Triticum aestivum L.) have been determined in order to develop an efficient system for transformation of Russian cultivars of spring wheat. Short-term (two days) cold treatment (4 degrees C) has been demonstrated to distinctly increase the frequency of morphogenetic callus induction. The optimal phytohormonal composition of the nutrient medium ensuring an in vitro regeneration rate of the common wheat cultivar Lada as high as 90% has been determined. The optimal temporal parameters of genetic transformation of wheat plants (10-14 days of culturing after initiation of a morphogenetic callus) have been determined for two transformation methods: biolistic without precipitated DNA and transformation with the plasmid psGFP-BAR. Analysis of the transient expression of the gfp gene has confirmed that 14 days of culturing is the optimal duration.

Antioxidant protection during ageing and senescence in chloroplasts of tobacco with modulated life span

We studied changes in antioxidant protection during ageing and senescence in chloroplasts of tobacco (Nicotiana tabacum L., cv. Wisconsin) with introduced SAG(12) promoter fused with ipt gene for cytokinin synthesis (transgenic plants with increased levels of cytokinins, SAG) or without it (control). Old leaves of SAG plants as well as their chloroplasts maintained higher physiological parameters compared to controls; accordingly, we concluded that their ageing was diverted due to increased cytokinin content. The chloroplast antioxidant protection did not decrease as well. Although antioxidant protection usually decreased in whole leaves of senescing control plants, ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR) activity, which maintained the high redox state of ascorbate, increased in chloroplasts of old control leaves.

Transformation by T-DNA integration causes highly sterile phenotype independent of transgenes in Arabidopsis thaliana

Agrobacterium tumefaciens-mediated gene transformation caused highly sterile phenotype in T1 transgenic populations of Arabidopsis thaliana. The phenomenon occurred independent of the genes and construct types used for transformation. The occurring frequency is less than 10% and the phenotype is inheritable. Intensive examination elucidated that the sterility is due to indehiscence or delayed dehiscence of the anthers during the flowering stage, resulting from the reduced or disordered endothecial secondary wall thickening of the anthers in the sterile flowers. Exogenous jasmonic acid application cannot rescue the sterile phenotype. Additionally, by using the Escherichia coli uidA gene encoding the beta-glucuronidase as a reporter gene, we indicated that the Cauliflower mosaic virus 35S promoter was not constitutively active as expected previously in the reproductive organs of Arabidopsis. These results contribute significantly to the plant community by suggesting that more careful examination and statistical analysis are needed while studying gain-of-function phenotypes of genes, especially for genes that might be involved in reproductive development.

SCAMPs highlight the developing cell plate during cytokinesis in tobacco BY-2 cells

We previously demonstrated that rice (Oryza sativa) SECRETORY CARRIER MEMBRANE PROTEIN1 (OsSCAMP1)-yellow fluorescent protein in transgenic tobacco (Nicotiana tabacum) Bright Yellow-2 cells locates to the plasma membrane and to motile punctate structures, which represent the trans-Golgi network/early endosome and are tubular-vesicular in nature. Here, we now show that SCAMPs are diverted to the cell plate during cytokinesis dividing Bright Yellow-2 cells. As cells progress from metaphase to cytokinesis, punctate OsSCAMP1-labeled structures begin to collect in the future division plane. Together with the internalized endosomal marker FM4-64, they then become incorporated into the cell plate as it forms and expands. This was confirmed by immunogold electron microscopy. We also monitored for the Golgi apparatus and the prevacuolar compartment (PVC)/multivesicular body. Golgi stacks tend to accumulate in the vicinity of the division plane, but the signals are clearly separate to the cell plate. The situation with the PVC (labeled by green fluorescent protein-BP-80) is not so clear. Punctate BP-80 signals are seen at the advancing periphery of the cell plate, which was confirmed by immunogold electron microscopy. Specific but weak labeling was observed in the cell plate, but no evidence for a fusion of the PVC/multivesicular body with the cell plate could be obtained. Our data, therefore, support the notion that cell plate formation is mainly a secretory process involving mass incorporation of domains of the trans-Golgi network/early endosome membrane. We regard the involvement of multivesicular late endosomes in this process to be equivocal.

Arabidopsis TONNEAU1 proteins are essential for preprophase band formation and interact with centrin

Plant cells have specific microtubule structures involved in cell division and elongation. The tonneau1 (ton1) mutant of Arabidopsis thaliana displays drastic defects in morphogenesis, positioning of division planes, and cellular organization. These are primarily caused by dysfunction of the cortical cytoskeleton and absence of the preprophase band of microtubules. Characterization of the ton1 insertional mutant reveals complex chromosomal rearrangements leading to simultaneous disruption of two highly similar genes in tandem, TON1a and TON1b. TON1 proteins are conserved in land plants and share sequence motifs with human centrosomal proteins. The TON1 protein associates with soluble and microsomal fractions of Arabidopsis cells, and a green fluorescent protein-TON1 fusion labels cortical cytoskeletal structures, including the preprophase band and the interphase cortical array. A yeast two-hybrid screen identified Arabidopsis centrin as a potential TON1 partner. This interaction was confirmed both in vitro and in plant cells. The similarity of TON1 with centrosomal proteins and its interaction with centrin, another key component of microtubule organizing centers, suggests that functions involved in the organization of microtubule arrays by the centrosome were conserved across the evolutionary divergence between plants and animals.

Glyco-engineering of biotherapeutic proteins in plants

Many therapeutic glycoproteins have been successfully generated in plants. Plants have advantages regarding practical and economic concerns, and safety of protein production over other existing systems. However, plants are not ideal expression systems for the production of biopharmaceutical proteins, due to the fact that they are incapable of the authentic human N-glycosylation process. The majority of therapeutic proteins are glycoproteins which harbor N-glycans, which are often essential for their stability, folding, and biological activity. Thus, several glyco-engineering strategies have emerged for the tailor-making of N-glycosylation in plants, including glycoprotein subcellular targeting, the inhibition of plant specific glycosyltranferases, or the addition of human specific glycosyltransferases. This article focuses on plant N-glycosylation structure, glycosylation variation in plant cell, plant expression system of glycoproteins, and impact of glycosylation on immunological function. Furthermore, plant glyco-engineering techniques currently being developed to overcome the limitations of plant expression systems in the production of therapeutic glycoproteins will be discussed in this review.

Expression of cell wall related genes in basal and ear internodes of silking brown-midrib-3, caffeic acid O-methyltransferase (COMT) down-regulated, and normal maize plants

BACKGROUND

Silage maize is a major forage and energy resource for cattle feeding, and several studies have shown that lignin content and structure are the determining factors in forage maize feeding value. In maize, four natural brown-midrib mutants have modified lignin content, lignin structure and cell wall digestibility. The greatest lignin reduction and the highest cell wall digestibility were observed in the brown-midrib-3 (bm3) mutant, which is disrupted in the caffeic acid O-methyltransferase (COMT) gene.

RESULTS

Expression of cell wall related genes was investigated in basal and ear internodes of normal, COMT antisens (AS225), and bm3 maize plants of the INRA F2 line. A cell wall macro-array was developed with 651 gene specific tags of genes specifically involved in cell wall biogenesis. When comparing basal (older lignifying) and ear (younger lignifying) internodes of the normal line, all genes known to be involved in constitutive monolignol biosynthesis had a higher expression in younger ear internodes. The expression of the COMT gene was heavily reduced, especially in the younger lignifying tissues of the ear internode. Despite the fact that AS225 transgene expression was driven only in sclerenchyma tissues, COMT expression was also heavily reduced in AS225 ear and basal internodes. COMT disruption or down-regulation led to differential expressions of a few lignin pathway genes, which were all over-expressed, except for a phenylalanine ammonia-lyase gene. More unexpectedly, several transcription factor genes, cell signaling genes, transport and detoxification genes, genes involved in cell wall carbohydrate metabolism and genes encoding cell wall proteins, were differentially expressed, and mostly over-expressed, in COMT-deficient plants.

CONCLUSION

Differential gene expressions in COMT-deficient plants highlighted a probable disturbance in cell wall assembly. In addition, the gene expressions suggested modified chronology of the different events leading to cell expansion and lignification with consequences far beyond the phenylpropanoid metabolism. The reduced availability of monolignols and S units in bm3 or AS225 plants led to plants also differing in cell wall carbohydrate, and probably protein, composition. Thus, the deficiency in a key-enzyme of the lignin pathway had correlative effects on the whole cell wall metabolism. Furthermore, the observed differential expression between bm3 and normal plants indicated the possible involvement in the maize lignin pathway of genes which up until now have not been considered to play this role.

High-resolution whole-mount imaging of three-dimensional tissue organization and gene expression enables the study of Phloem development and structure in Arabidopsis

Currently, examination of the cellular structure of plant organs and the gene expression therein largely relies on the production of tissue sections. Here, we present a staining technique that can be used to image entire plant organs using confocal laser scanning microscopy. This technique produces high-resolution images that allow three-dimensional reconstruction of the cellular organization of plant organs. Importantly, three-dimensional domains of gene expression can be analyzed with single-cell precision. We used this technique for a detailed examination of phloem cells in the wild type and mutants. We were also able to recognize phloem sieve elements and their differentiation state in any tissue type and visualize the structure of sieve plates. We show that in the altered phloem development mutant, a hybrid cell type with phloem and xylem characteristics develops from initially normally differentiated protophloem cells. The simplicity of sieve element data collection allows for the statistical analysis of structural parameters of sieve plates, essential for the calculation of phloem conductivity. Taken together, this technique significantly improves the speed and accuracy of the investigation of plant growth and development.

Targeted degradation of the cyclin-dependent kinase inhibitor ICK4/KRP6 by RING-type E3 ligases is essential for mitotic cell cycle progression during Arabidopsis gametogenesis

Following meiosis, plant gametophytes develop through two or three rounds of mitosis. Although the ontogeny of gametophyte development has been defined in Arabidopsis thaliana, the molecular mechanisms regulating mitotic cell cycle progression are not well understood. Here, we report that RING-H2 group F 1a (RHF1a) and RHF2a, two RING-finger E3 ligases, play an important role in Arabidopsis gametogenesis. The rhf1a rhf2a double mutants are defective in the formation of male and female gametophytes due to interphase arrest of the mitotic cell cycle at the microspore stage of pollen development and at female gametophyte stage 1 of embryo sac development. We demonstrate that RHF1a directly interacts with and targets a cyclin-dependent kinase inhibitor ICK4/KRP6 (for Interactors of Cdc2 Kinase 4/Kip-related protein 6) for proteasome-mediated degradation. Inactivation of the two redundant RHF genes leads to the accumulation of ICK4/KRP6, and reduction of ICK4/KRP6 expression largely rescues the gametophytic defects in rhf1a rhf2a double mutants, indicating that ICK4/KRP6 is a substrate of the RHF E3 ligases. Interestingly, in situ hybridization showed that ICK4/KRP6 was predominantly expressed in sporophytes during meiosis. Our findings indicate that RHF1a/2a-mediated degradation of the meiosis-accumulated ICK4/KRP6 is essential to ensure the progression of subsequent mitoses to form gametophytes in Arabidopsis.

Mutation of Arabidopsis BARD1 causes meristem defects by failing to confine WUSCHEL expression to the organizing center

Stem cell fate in the Arabidopsis thaliana shoot apical meristem (SAM) is controlled by WUSCHEL (WUS) and CLAVATA. Here, we examine BARD1 (for BRCA1-associated RING domain 1), which had previously been implicated in DNA repair functions; we find that it also regulates WUS expression. We observed severe SAM defects in the knockout mutant bard1-3. WUS transcripts accumulated >238-fold in bard1-3 compared with the wild type and were located mainly in the outermost cell layers instead of the usual organizing center. A specific WUS promoter region was recognized by nuclear protein extracts obtained from wild-type plants, and this protein-DNA complex was recognized by antibodies against BARD1. The double mutant (wus-1 bard1-3) showed prematurely terminated SAM structures identical to those of wus-1, indicating that BARD1 functions through regulation of WUS. BARD1 overexpression resulted in reduced WUS transcript levels, giving a wus-1-like phenotype. Either full-length BARD1 or a clone that encoded the C-terminal domain (BARD1:C-ter;bard1-3) was sufficient to complement the bard1-3 phenotype, indicating that BARD1 functions through its C-terminal domain. Our data suggest that BARD1 regulates SAM organization and maintenance by limiting WUS expression to the organizing center.

Truncated myosin XI tail fusions inhibit peroxisome, Golgi, and mitochondrial movement in tobacco leaf epidermal cells: a genetic tool for the next generation

Although organelle movement in higher plants is predominantly actin-based, potential roles for the 17 predicted Arabidopsis myosins in motility are only just emerging. It is shown here that two Arabidopsis myosins from class XI, XIE, and XIK, are involved in Golgi, peroxisome, and mitochondrial movement. Expression of dominant negative forms of the myosin lacking the actin binding domain at the amino terminus perturb organelle motility, but do not completely inhibit movement. Latrunculin B, an actin destabilizing drug, inhibits organelle movement to a greater extent compared to the effects of AtXIE-T/XIK-T expression. Amino terminal YFP fusions to XIE-T and XIK-T are dispersed throughout the cytosol and do not completely decorate the organelles whose motility they affect. XIE-T and XIK-T do not affect the global actin architecture, but their movement and location is actin-dependent. The potential role of these truncated myosins as genetically encoded inhibitors of organelle movement is discussed.

Agroinfiltration of grapevine leaves for fast transient assays of gene expression and for long-term production of stable transformed cells

Agrobacterium-mediated transient assays for the analysis of gene function are used as alternatives to genetic complementation and stable plant transformation. Although such assays are routinely performed in several plant species, they have not yet been successfully applied to grapevines. We explored genetic background diversity of grapevine cultivars and performed agroinfiltration into in vitro cultured plants. By combining different genotypes and physiological conditions, we developed a protocol for efficient transient transformations of selected grapevine cultivars. Among the four cultivars analyzed, Sugraone and Aleatico exhibited high levels of transient transformation. Transient expression occurred in the majority of cells within the infiltrated tissue several days after agroinfiltration and, in a few cases, it later spread to a larger portion of the leaf. Three laboratory strains of Agrobacterium tumefaciens with different virulence levels were used for agroinfiltration assays on grapevine plants. This method promises to be a powerful tool to perform subcellular localization analyses. Grapevine leaf tissues were transformed with fluorescent markers targeted to cytoplasm (free GFP and mRFP1), endoplasmatic reticulum (GFP::HDEL), chloroplast (GAPA1::YFP) and mitochondria (beta::GFP). Confocal microscope analyses demonstrated that these subcellular compartments could be easily visualized in grapevine leaf cells. In addition, from leaves of the Sugraone cultivar agroinfiltrated with endoplasmic reticulum-targeted GFP-construct, stable transformed cells were obtained that show the opportunity to convert a transiently transformed leaf tissue into a stably transformed cell line.

The chimeric cyclic nucleotide-gated ion channel ATCNGC11/12 constitutively induces programmed cell death in a Ca2+ dependent manner

The hypersensitive response (HR) involves programmed cell death (PCD) in response to pathogen infection. To investigate the pathogen resistance signaling pathway, we previously identified the Arabidopsis mutant cpr22, which displays constitutive activation of multiple defense responses including HR like cell death. The cpr22 mutation has been identified as a 3 kb deletion that fuses two cyclic nucleotide-gated ion channel (CNGC)-encoding genes, ATCNGC11 and ATCNGC12, to generate a novel chimeric gene, ATCNGC11/12. In this study, we conducted a characterization of cell death induced by transient expression of ATCNGC11/12 in Nicotiana benthamiana. Electron microscopic analysis of this cell death showed similar characteristics to PCD, such as plasma membrane shrinkage and vesicle formation. The hallmark of animal PCD, fragmentation of nuclear DNA, was also observed in ATCNGC11/12-induced cell death. The development of cell death was significantly suppressed by caspase-1 inhibitors, suggesting the involvement of caspases in this process. Recently, vacuolar processing enzyme (VPE) was isolated as the first plant caspase-like protein, which is involved in HR development. In VPE-silenced plants development of cell death induced by ATCNGC11/12 was much slower and weaker compared to control plants, suggesting the involvement of VPE as a caspase in ATCNGC11/12-induced cell death. Complementation analysis using a Ca2+ uptake deficient yeast mutant demonstrated that the ATCNGC11/12 channel is permeable to Ca2+. Additionally, calcium channel blockers such as GdCl3 inhibited ATCNGC11/12-induced HR formation, whereas potassium channel blockers did not. Taken together, these results indicate that the cell death that develops in the cpr22 mutant is indeed PCD and that the chimeric channel, ATCNGC11/12, is at the point of, or up-stream of the calcium signal necessary for the development of HR.

The illuminated plant cell

The past decade has provided biologists with a palette of genetically encoded, multicolored fluorescent proteins. The living plant cell turned into a 'coloring book' and today, nearly every text-book organelle has been highlighted in scintillating fluorescent colors. This review provides a concise listing of the earliest representative fluorescent-protein probes used to highlight various targets within the plant cell, and introduces the idea of using the numerous multicolor, subcellular probes for the development of an early intracellular response profile of plants.

LeERF1 positively modulated ethylene triple response on etiolated seedling, plant development and fruit ripening and softening in tomato

To study the function of LeERF1 in ethylene triple response on etiolated seedling, plant development and fruit ripening and softening, LeERF1 gene was introduced into tomato (Lycopersicon esculentum cv. No. 4 Zhongshu) through Agrobacterium-mediated transformation. The sense LeERF1 and anti-sense LeERF1 transgenic tomato were obtained. Overexpression of LeERF1 in tomato caused the typical ethylene triple response on etiolated seedling. In the adult stage, 35S::LeERF1 resulted in morphological changes in the leaves of the LeERF1-sn lines. Anti-sense LeERF1 fruits had longer shelf life compared with wild-type tomato. The results of this manuscript indicated that LeERF1 positively mediated the ethylene signals, while the function of LeERF1 was verified for the first time to be positively related with ethylene triple response on etiolated seedling, plant development and fruit ripening and softening using LeERF1-sn, wt and LeERF1-as tomato.

Direct creation of marker-free tobacco plants from agroinfiltrated leaf discs

Agroinfiltration is employed as a fast way to directly create marker-free transgenic tobacco plants. As an example for the efficiency of the method, Agrobacterium cells harboring a marker-free vector coding for beta-glucuronidase (GUS) were infiltrated into the leaf discs of Nicotiana tabacum, which were then used as explants for marker-free plant regeneration by tissue culture. Through GUS staining, a large number of small calli were shown to be stably transformed on the treated leaf discs at 17 days after agroinfiltration. Most importantly, after continuous culture of the leaf discs until shoot regeneration, about 15% of the regenerants were proven to be transformants by polymerase chain reaction (PCR) analysis.

Capsicum annuum CCR4-associated factor CaCAF1 is necessary for plant development and defence response

The CCR4-associated factor 1 (CAF1) protein belongs to the CCR4-NOT complex, which is an evolutionary conserved protein complex and plays an important role in the control of transcription and mRNA decay in yeast and mammals. To investigate the function of CAF1 in plants, we performed gain- and loss-of-function studies by overexpression of the pepper CAF1 (CaCAF1) in tomato and virus-induced gene silencing (VIGS) of the gene in pepper plants. Overexpression of CaCAF1 in tomato resulted in significant growth enhancement, with increasing leaf thickness, and enlarged cell size by more than twofold when compared with the control plants. A transmission electron microscopic analysis revealed that the CaCAF1-transgenic tomato plants had thicker cell walls and cuticle layers than the control plants. In addition to developmental changes, overexpression of CaCAF1 in tomato plants resulted in enhanced resistance against the oomycete pathogen Phytophthora infestans. Additionally, microarray, northern and real-time polymerase chain reaction analyses of CaCAF1-transgenic tomato plants revealed that multiple genes were constitutively upregulated, including genes involved in polyamine biosynthesis, defence reactions and cell-wall organogenesis. In contrast, VIGS of CaCAF1 in pepper plants caused significant growth retardation and enhanced susceptibility to the pepper bacterial spot pathogen Xanthomonas axonopodis pv. vesicatoria. Our results suggest roles for plant CAF1 in normal growth and development, as well as in defence against pathogens.

TERE; a novel cis-element responsible for a coordinated expression of genes related to programmed cell death and secondary wall formation during differentiation of tracheary elements

The differentiation of water-conducting tracheary elements (TEs) is the result of the orchestrated construction of secondary wall structure, including lignification, and programmed cell death (PCD), including cellular autolysis. To understand the orchestrated regulation of differentiation of TEs, we investigated the regulatory mechanism of gene expression directing TE differentiation. Detailed loss-of-function and gain-of-function analyses of the ZCP4 (Zinniacysteine protease 4) promoter, which confers TE-specific expression, demonstrated that a novel 11-bp cis-element is necessary and sufficient for the immature TE-specific promoter activity. The 11-bp cis-element-like sequences were found in promoters of many Arabidopsis TE differentiation-related genes. A gain-of-function analysis with similar putative cis-elements from secondary wall formation or modification-related genes as well as PCD-related genes indicated that the cis-elements are also sufficient for TE-specific expression of genes. These results demonstrate that a common sequence, designated as the tracheary-element-regulating cis-element, confers TE-specific expression to both genes related to secondary wall formation or modification and PCD.

Characterization of vascular-specific RSs1 and rolC promoters for their utilization in engineering plants to develop resistance against hemipteran insect pests

Rice sucrose synthase1, RSs1 (isolated from rice) and rolC (isolated from Agrobacterium rhizogenes) promoters were evaluated by binding analyses of their respective cis-elements with host nuclear transcription factors. The expression profile of an insecticidal protein driven by these promoters in transgenic plants was monitored. Motif-search analysis with available phloem-specific promoter sequences revealed the presence of two BoxII elements in RSs1. An octopine synthase element, a stem-specific, a root-specific and a light-responsive element were found in the rolC promoter, whereas the ASL box, GATA and 13 bp motifs were detected in both promoters. Binding analysis of these cis-elements (both in native and mutant forms) with the trans-factors present in the nuclear extracts from rice, tobacco and chickpea, followed by electrophoretic mobility shift assay, documented a highly specific cis-trans interaction. Both promoters were utilized to express Allium sativum leaf agglutinin (ASAL) gene in the three aforementioned plant systems. By immunohistochemistry and immunohistofluorescence, specific patterns of ASAL accumulation were detected in vascular tissues of single copy transgenic plants. Transgenic plants expressing ASAL in a phloem-specific manner demonstrated about 60-65% more insecticidal activity than control plants. The two promoters, which evolved independently from two distinctly unrelated origins, were found to maintain their functionality in a conserved manner. They were able to express the insecticidal protein coding ASAL as transgene both in monocot and dicot hosts. Thus, the two promoters are valuable as prospective phloem-specific promoters for use in plant biotechnological programmes.

Metabolic diversion of the phenylpropanoid pathway causes cell wall and morphological changes in transgenic tobacco stems

Studies involving transgenic plants with modifications in the lignin pathway reported to date, have received a relatively preliminary characterisation in relation to the impact on vascular integrity, biomechanical properties of tissues and carbon allocation to phenolic pools. Therefore, in this study transgenic tobacco plants (Nicotiana tabacum cv XHFD 8) expressing various levels of a bacterial 4-hydroxycinnamoyl-CoA hydratase/lyase (HCHL) gene have been characterised for cell wall and related morphological changes. The HCHL enzyme converts p-coumaroyl-CoA to 4-hydroxybenzaldehyde thereby rerouting the phenylpropanoid pathway. Plants expressing high levels of HCHL activity exhibited reduced lignin deposition, impaired monolignol biosynthesis and vascular integrity. The plants also exhibited reduction in stem toughness concomitant with a massive reduction in both the cell wall esterified and soluble phenolics. A notable result of redirecting the carbon flux was the wall-bound accretion of vanillin and vanillic acid, probably due to the shunt pathway. Intracellular accumulation of novel metabolites such as hydroxybenzoic and vanillic acid derivatives also occurred in the transgenic plants. A line with intermediate levels of HCHL expression conferred correspondingly reduced lignin deposition, toughness and phenolics. This line displayed a normal morphology but distorted vasculature. Coloration of the xylem has been previously attributed to incorporation of alternative phenolics, whereas results from this study indicate that the coloration is likely to be due to the association of low molecular weight phenolics. There was no evidence of increased growth or enhanced cellulose biosynthesis as a result of HCHL expression. Hence, rerouting the phenylpropanoid biosynthetic pathway quantitatively and qualitatively modifies cell wall-bound phenolics and vascular structure.