Modified binary plant transformation vectors with the wild-type gene encoding NPTII

The RPT2a-MET1 axis regulates TERMINAL FLOWER1 to control inflorescence meristem indeterminacy in Arabidopsis

Plant inflorescence architecture is determined by inflorescence meristem (IM) activity and controlled by genetic mechanisms associated with environmental factors. In Arabidopsis (Arabidopsis thaliana), TERMINAL FLOWER1 (TFL1) is expressed in the IM and is required to maintain indeterminate growth, whereas LEAFY (LFY) is expressed in the floral meristems (FMs) formed at the periphery of the IM and is required to activate determinate floral development. Here, we address how Arabidopsis indeterminate inflorescence growth is determined. We show that the 26S proteasome subunit REGULATORY PARTICLE AAA-ATPASE 2a (RPT2a) is required to maintain the indeterminate inflorescence architecture in Arabidopsis. rpt2a mutants display reduced TFL1 expression levels and ectopic LFY expression in the IM and develop a determinate zigzag-shaped inflorescence. We further found that RPT2a promotes DNA METHYLTRANSFERASE1 degradation, leading to DNA hypomethylation upstream of TFL1 and high TFL1 expression levels in the wild-type IM. Overall, our work reveals that proteolytic input into the epigenetic regulation of TFL1 expression directs inflorescence architecture in Arabidopsis, adding an additional layer to stem cell regulation.

CRISPR-Cas9 Arabidopsis mutants of genes for ARPC1 and ARPC3 subunits of ARP2/3 complex reveal differential roles of complex subunits

Protein complex Arp2/3 has a conserved role in the nucleation of branched actin filaments. It is constituted of seven subunits, including actin-like subunits ARP2 and ARP3 plus five other subunits called Arp2/3 Complex Component 1 to 5, which are not related to actin. Knock-out plant mutants lacking individual plant ARP2/3 subunits have a typical phenotype of distorted trichomes, altered pavement cells shape and defects in cell adhesion. While knock-out mutant Arabidopsis plants for most ARP2/3 subunits have been characterized before, Arabidopsis plant mutants missing ARPC1 and ARPC3 subunits have not yet been described. Using CRISPR/Cas9, we generated knock-out mutants lacking ARPC1 and ARPC3 subunits. We confirmed that the loss of ARPC1 subunits results in the typical ARP2/3 mutant phenotype. However, the mutants lacking ARPC3 subunits resulted in plants with surprisingly different phenotypes. Our results suggest that plant ARP2/3 complex function in trichome shaping does not require ARPC3 subunit, while the fully assembled complex is necessary for the establishment of correct cell adhesion in the epidermis.

Constitutive expression of JASMONATE RESISTANT 1 induces molecular changes that prime the plants to better withstand drought

In this study, we investigated Arabidopsis thaliana plants with altered levels of the enzyme JASMONATE RESISTANT 1 (JAR1), which converts jasmonic acid (JA) to jasmonoyl-l-isoleucine (JA-Ile). Analysis of a newly generated overexpression line (35S::JAR1) revealed that constitutively increased JA-Ile production in 35S::JAR1 alters plant development, resulting in stunted growth and delayed flowering. Under drought-stress conditions, 35S::JAR1 plants showed reduced wilting and recovered better from desiccation than the wild type. By contrast, jar1-11 plants with a strong reduction in JA-Ile content were hypersensitive to drought. RNA-sequencing analysis and hormonal profiling of plants under normal and drought conditions provided insights into the molecular reprogramming caused by the alteration in JA-Ile content. Especially 35S::JAR1 plants displayed changes in expression of developmental genes related to growth and flowering. Further transcriptional differences pertained to drought-related adaptive systems, including stomatal density and aperture, but also reactive oxygen species production and detoxification. Analysis of wild type and jar1-11 plants carrying the roGFP-Orp1 sensor support a role of JA-Ile in the alleviation of methyl viologen-induced H₂ O₂ production. Our data substantiate a role of JA-Ile in abiotic stress response and suggest that JAR1-mediated increase in JA-Ile content primes Arabidopsis towards improved drought stress tolerance.

Overexpression of pea α-carboxyltransferase in Arabidopsis and camelina increases fatty acid synthesis leading to improved seed oil content

Heteromeric acetyl‐CoA carboxylase (htACCase) catalyzes the committed step of de novo fatty acid biosynthesis in most plant plastids. Plant htACCase is comprised of four subunits: α‐ and β‐carboxyltransferase (α‐ and β‐CT), biotin carboxylase, and biotin carboxyl carrier protein. Based on in vivo absolute quantification of htACCase subunits, α‐CT is 3‐ to 10‐fold less abundant than its partner subunit β‐CT in developing Arabidopsis seeds [Wilson and Thelen, J. Proteome Res., 2018, 17 (5)]. To test the hypothesis that low expression of α‐CT limits htACCase activity and flux through fatty acid synthesis in planta, we overexpressed Pisum sativum α‐CT, either with or without its C‐terminal non‐catalytic domain, in both Arabidopsis thaliana and Camelina sativa. First‐generation Arabidopsis seed of 35S::Ps α‐CT (n = 25) and 35S::Ps α‐CTΔ406‐875 (n = 47) were on average 14% higher in oil content (% dry weight) than wild type co‐cultivated in a growth chamber. First‐generation camelina seed showed an average 8% increase compared to co‐cultivated wild type. Biochemical analyses confirmed the accumulation of Ps α‐CT and Ps α‐CTΔ406‐875 protein and higher htACCase activity in overexpression lines during early seed development. Overexpressed Ps α‐CT co‐migrated with native At β‐CT during anion exchange chromatography, indicating co‐association. By successfully increasing seed oil content upon heterologous overexpression of α‐CT, we demonstrate how absolute quantitation of in vivo protein complex stoichiometry can be used to guide rational metabolic engineering.

Phyllotactic patterning of gerbera flower heads

Phyllotaxis, the distribution of organs such as leaves and flowers on their support, is a key attribute of plant architecture. The geometric regularity of phyllotaxis has attracted multidisciplinary interest for centuries, resulting in an understanding of the patterns in the model plants Arabidopsis and tomato down to the molecular level. Nevertheless, the iconic example of phyllotaxis, the arrangement of individual florets into spirals in the heads of the daisy family of plants (Asteraceae), has not been fully explained. We integrate experimental data and computational models to explain phyllotaxis in Gerbera hybrida We show that phyllotactic patterning in gerbera is governed by changes in the size of the morphogenetically active zone coordinated with the growth of the head. The dynamics of these changes divides the patterning process into three phases: the development of an approximately circular pattern with a Fibonacci number of primordia near the head rim, its gradual transition to a zigzag pattern, and the development of a spiral pattern that fills the head on the template of this zigzag pattern. Fibonacci spiral numbers arise due to the intercalary insertion and lateral displacement of incipient primordia in the first phase. Our results demonstrate the essential role of the growth and active zone dynamics in the patterning of flower heads.

WRKY42 transcription factor positively regulates leaf senescence through modulating SA and ROS synthesis in Arabidopsis thaliana

Leaf senescence represents the final stage of leaf growth and development, and its onset and progression are strictly regulated; however, the underlying regulatory mechanisms remain largely unknown. In this study we found that WRKY42 was highly induced during leaf senescence. Loss-of-function wrky42 mutants showed delayed leaf senescence whereas the overexpression of WRKY42 accelerated senescence. Transcriptome analysis revealed 2721 differentially expressed genes between wild-type and WRKY42-overexpressing plants, including genes involved in salicylic acid (SA) and reactive oxygen species (ROS) synthesis as well as several senescence-associated genes (SAGs). Moreover, WRKY42 activated the transcription of isochorismate synthase 1 (ICS1), respiratory burst oxidase homolog F (RbohF) and a few SAG genes. Consistently, the expression of these genes was reduced in wrky42 mutants but was markedly increased in transgenic Arabidopsis overexpressing WRKY42. Both in vitro electrophoretic mobility shift assays (EMSAs) and in vivo chromatin immunoprecipitation and dual luciferase assays demonstrated that WRKY42 directly bound to the promoters of ICS1 and RbohF, as well as a few SAGs, to activate their expression. Genetic analysis further showed that mutations of ICS1 and RbohF suppressed the early senescence phenotype evoked by WRKY42 overexpression. Thus, we have identified WRKY42 as a novel transcription factor positively regulating leaf senescence by directly activating the transcription of ICS1, RbohF and SAGs, without any seed yield penalty.

Punicic acid production in Brassica napus

Punicic acid (PuA; 18:3Δ^{9cis,11trans,13cis}), a conjugated linolenic acid isomer bearing three conjugated double bonds, is associated with various health benefits and has potential for industrial use. The major nature source of this unusual fatty acid is pomegranate (Punica granatum) seed oil, which contains up to 80% (w/w) of its fatty acids as PuA. Pomegranate seed oil, however, is low yielding with unstable production and thus limits the supply of PuA. Metabolic engineering of established temperate oil crops for PuA production, therefore, has the potential to be a feasible strategy to overcome the limitations associated with sourcing PuA from pomegranate. In this study, the cDNAs encoding a pomegranate fatty acid conjugase and a pomegranate oleate desaturase were co-expressed in canola-type Brassica napus. Transgenic B. napus lines accumulated up to 11% (w/w) of the total fatty acids as PuA in the seed oil, which is the highest level of PuA reported in metabolically engineered oilseed crops so far. Levels of seed oil PuA were stable over two generations and had no negative effects on seed germination. The transgenic B. napus lines with the highest PuA levels contained multiple transgene insertions and the PuA content of B. napus seed oil was correlated with efficiency of oleic acid desaturation and linoleic acid conjugation. In addition, PuA accumulated at lower levels in polar lipids (5.0-6.9%) than triacylglycerol (7.5-10.6%), and more than 60% of triacylglycerol-associated PuA was present at the sn-2 position. This study provides the basis for the commercial production of PuA in transgenic oilseed crops and thus would open new prospects for the application of this unusual fatty acid in health and industry.

Arp2/3 Complex Is Required for Auxin-Driven Cell Expansion Through Regulation of Auxin Transporter Homeostasis

The Arp2/3 complex is an actin nucleator shown to be required throughout plant morphogenesis, contributing to processes such as cell expansion, tissue differentiation or cell wall assembly. A recent publication demonstrated that plants lacking functional Arp2/3 complex also present defects in auxin distribution and transport. This work shows that Arp2/3 complex subunits are predominantly expressed in the provasculature, although other plant tissues also show promoter activity (e.g., cotyledons, apical meristems, or root tip). Moreover, auxin can trigger subunit expression, indicating a role of this phytohormone in mediating the complex activity. Further investigation of the functional interaction between Arp2/3 complex and auxin signaling also reveals their cooperation in determining pavement cell shape, presumably through the role of Arp2/3 complex in the correct auxin carrier trafficking. Young seedlings of arpc5 mutants show increased auxin-triggered proteasomal degradation of DII-VENUS and altered PIN3 distribution, with higher levels of the protein in the vacuole. Closer observation of vacuolar morphology revealed the presence of a more fragmented vacuolar compartment when Arp2/3 function is abolished, hinting a generalized role of Arp2/3 complex in endomembrane function and protein trafficking.

The High Light Response in Arabidopsis Requires the Calcium Sensor Protein CAS, a Target of STN7- and STN8-Mediated Phosphorylation

Reversible phosphorylation of thylakoid proteins contributes to photoacclimation responses in photosynthetic organisms, enabling the fine-tuning of light harvesting under changing light conditions and promoting the onset of photoprotective processes. However, the precise functional role of many of the described phosphorylation events on thylakoid proteins remains elusive. The calcium sensor receptor protein (CAS) has previously been indicated as one of the targets of the state transition kinase 8 (STN8). Here we show that in Arabidopsis thaliana, CAS is also phosphorylated by the state transition kinase 7 (STN7), as well as by another, so-far unknown, Ca2+-dependent kinase. Phosphoproteomics analysis and in vitro phosphorylation assays on CAS variants identified the phylogenetically conserved residues Thr-376, Ser-378, and Thr-380 as the major phosphorylation sites of the STN kinases. Spectroscopic analyses of chlorophyll fluorescence emission at 77K further showed that, while the cas mutant is not affected in state transition, it displays a persistent strong excitation of PSI under high light exposure, similar to the phenotype previously observed in other mutants defective in photoacclimation mechanisms. Together with the observation of a strong concomitant phosphorylation of light harvesting complex II (LHCII) and photosynthetic core proteins under high irradiance in the cas mutant this suggests a role for CAS in the STN7/STN8/TAP38 network of phosphorylation-mediated photoacclimation processes in Arabidopsis.

Brassica rapa hairy root based expression system leads to the production of highly homogenous and reproducible profiles of recombinant human alpha-L-iduronidase

The Brassica rapa hairy root based expression platform, a turnip hairy root based expression system, is able to produce human complex glycoproteins such as the alpha-L-iduronidase (IDUA) with an activity similar to the one produced by Chinese Hamster Ovary (CHO) cells. In this article, a particular attention has been paid to the N- and O-glycosylation that characterize the alpha-L-iduronidase produced using this hairy root based system. This analysis showed that the recombinant protein is characterized by highly homogeneous post translational profiles enabling a strong batch to batch reproducibility. Indeed, on each of the 6 N-glycosylation sites of the IDUA, a single N-glycan composed of a core Man3 GlcNAc2 carrying one beta(1,2)-xylose and one alpha(1,3)-fucose epitope (M3XFGN2) was identified, highlighting the high homogeneity of the production system. Hydroxylation of proline residues and arabinosylation were identified during O-glycosylation analysis, still with a remarkable reproducibility. This platform is thus positioned as an effective and consistent expression system for the production of human complex therapeutic proteins.

Quantitative phosphoproteomics reveals the role of the AMPK plant ortholog SnRK1 as a metabolic master regulator under energy deprivation

Since years, research on SnRK1, the major cellular energy sensor in plants, has tried to define its role in energy signalling. However, these attempts were notoriously hampered by the lethality of a complete knockout of SnRK1. Therefore, we generated an inducible amiRNA::SnRK1α2 in a snrk1α1 knock out background (snrk1α1/α2) to abolish SnRK1 activity to understand major systemic functions of SnRK1 signalling under energy deprivation triggered by extended night treatment. We analysed the in vivo phosphoproteome, proteome and metabolome and found that activation of SnRK1 is essential for repression of high energy demanding cell processes such as protein synthesis. The most abundant effect was the constitutively high phosphorylation of ribosomal protein S6 (RPS6) in the snrk1α1/α2 mutant. RPS6 is a major target of TOR signalling and its phosphorylation correlates with translation. Further evidence for an antagonistic SnRK1 and TOR crosstalk comparable to the animal system was demonstrated by the in vivo interaction of SnRK1α1 and RAPTOR1B in the cytosol and by phosphorylation of RAPTOR1B by SnRK1α1 in kinase assays. Moreover, changed levels of phosphorylation states of several chloroplastic proteins in the snrk1α1/α2 mutant indicated an unexpected link to regulation of photosynthesis, the main energy source in plants.

The calmodulin-like proteins AtCML4 and AtCML5 are single-pass membrane proteins targeted to the endomembrane system by an N-terminal signal anchor sequence

Calmodulins (CaMs) are important mediators of Ca(2+) signals that are found ubiquitously in all eukaryotic organisms. Plants contain a unique family of calmodulin-like proteins (CMLs) that exhibit greater sequence variance compared to canonical CaMs. The Arabidopsis thaliana proteins AtCML4 and AtCML5 are members of CML subfamily VII and possess a CaM domain comprising the characteristic double pair of EF-hands, but they are distinguished from other members of this subfamily and from canonical CaMs by an N-terminal extension of their amino acid sequence. Transient expression of yellow fluorescent protein-tagged AtCML4 and AtCML5 under a 35S-promoter in Nicotiana benthamiana leaf cells revealed a spherical fluorescence pattern. This pattern was confirmed by transient expression in Arabidopsis protoplasts under the native promoter. Co-localization analyses with various endomembrane marker proteins suggest that AtCML4 and AtCML5 are localized to vesicular structures in the interphase between Golgi and the endosomal system. Further studies revealed AtCML5 to be a single-pass membrane protein that is targeted into the endomembrane system by an N-terminal signal anchor sequence. Self-assembly green fluorescent protein and protease protection assays support a topology with the CaM domain exposed to the cytosolic surface and not the lumen of the vesicles, indicating that AtCML5 could sense Ca(2+) signals in the cytosol. Phylogenetic analysis suggests that AtCML4 and AtCML5 are closely related paralogues originating from a duplication event within the Brassicaceae family. CML4/5-like proteins seem to be universally present in eudicots but are absent in some monocots. Together these results show that CML4/5-like proteins represent a flowering plant-specific subfamily of CMLs with a potential function in vesicle transport within the plant endomembrane system.

Cotranslational coat protein-mediated inhibition of potyviral RNA translation

Potato virus A (PVA) is a single-stranded positive-sense RNA virus and a member of the family Potyviridae. The PVA coat protein (CP) has an intrinsic capacity to self-assemble into filamentous virus-like particles, but the mechanism responsible for the initiation of viral RNA encapsidation in vivo remains unclear. Apart from virion assembly, PVA CP is also involved in the inhibition of viral RNA translation. In this study, we show that CP inhibits PVA RNA translation in a dose-dependent manner, through a mechanism involving the CP-encoding region. Analysis of this region, however, failed to identify any RNA secondary structure(s) preferentially recognized by CP, suggesting that the inhibition depends on CP-CP rather than CP-RNA interactions. In agreement with this possibility, insertion of an in-frame stop codon upstream of the CP sequence led to a marked decrease in the inhibition of viral RNA translation. Based on these results, we propose a model in which the cotranslational interactions between excess CP accumulating in trans and CP translated from viral RNA in cis are required to initiate the translational repression. This model suggests a mechanism for how viral RNA can be sequestered from translation and specifically selected for encapsidation at the late stages of viral infection.

IMPORTANCE

The main functions of the CP during potyvirus infection are to protect viral RNA from degradation and to transport it locally, systemically, and from host to host. Although virion assembly is a key step in the potyviral infectious cycle, little is known about how it is initiated and how viral RNA is selected for encapsidation. The results presented here suggest that CP-CP rather than CP-RNA interactions are predominantly involved in the sequestration of viral RNA away from translation. We propose that the cotranslational nature of these interactions may represent a mechanism for the selection of viral RNA for encapsidation. A better understanding of the mechanism of virion assembly may lead to development of crops resistant to potyviruses at the level of viral RNA encapsidation, thereby reducing the detrimental effects of potyvirus infections on food production.

In vivo functional analysis of a nuclear restorer PPR protein

BACKGROUND

Nuclear restorers of cytoplasmic male fertility (CMS) act to suppress the male sterile phenotype by down-regulating the expression of novel CMS-specifying mitochondrial genes. One such restorer gene is Rfo, which restores fertility to the radish Ogura or ogu CMS. Rfo, like most characterized restorers, encodes a pentatricopeptide repeat (PPR) protein, a family of eukaryotic proteins characterized by tandem repeats of a 35 amino acid motif. While over 400 PPR genes are found in characterized plant genomes and the importance of this gene family in organelle gene expression is widely recognized, few detailed in vivo assessments of primary structure-function relationships in this protein family have been conducted.

RESULTS

In contrast to earlier studies, which identified 16 or 17 PPR domains in the Rfo protein, we now find, using a more recently developed predictive tool, that Rfo has 18 repeat domains with the additional domain N-terminal to the others. Comparison of transcript sequences from pooled rfo/rfo plants with pooled Rfo/Rfo plants of a mapping population led to the identification of a non-restoring rfo allele with a 12 bp deletion in the fourth domain. Introduction into ogu CMS plants of a genetic construct in which this deletion had been introduced into Rfo led to a partial loss in the capacity to produce viable pollen, as assessed by vital staining, pollen germination and the capacity for seed production following pollination of CMS plants. The degree of viable pollen production among different transgenic plants roughly correlated with the copy number of the introduced gene and with the reduction of the levels of the ORF138 CMS-associated protein. All other constructs tested, including one in which only the C-terminal PPR repeat was deleted and another in which this repeat was replaced by the corresponding domain of the related, non-restoring gene, PPR-A, failed to result in any measure of fertility restoration.

CONCLUSIONS

The identification of the additional PPR domain in Rfo indicates that the protein, apart from its N-terminal mitochondrial targeting presequence, consists almost entirely of PPR repeats. The newly identified rfo allele carries the same 4 amino acid deletion as that found in the neighboring, related, non-restoring PPR gene, PPR-A. Introduction of this four amino acid deletion into a central domain the Rfo protein, however, only partially reduces its restoration capacity, even though this alteration might be expected to alter the spacing between the adjoining repeats. All other tested alterations, generated by deleting specific PPR repeats or exchanging repeats with corresponding domains of PPR-A, led to a complete loss of restorer function. Overall we demonstrate that introduction of targeted alterations of Rfo into ogu CMS plants provides a sensitive in vivo readout for analysis of the relationship between primary structure and biological function in this important family of plant proteins.

Combined transgenic expression of Punica granatum conjugase (FADX) and FAD2 desaturase in high linoleic acid Arabidopsis thaliana mutant leads to increased accumulation of punicic acid

Arabidopsis was engineered to produce 21.2 % punicic acid in the seed oil. Possible molecular factors limiting further accumulation of the conjugated fatty acid were investigated. Punicic acid (18:3Δ(9cis,11trans,13cis) ) is a conjugated linolenic acid isomer and is a main component of Punica granatum (pomegranate) seed oil. Medical studies have shown that punicic acid is a nutraceutical with anti-cancer and anti-obesity properties. It has been previously demonstrated that the conjugated double bonds in punicic acid are produced via the catalytic action of fatty acid conjugase (FADX), which is a homolog of the oleate desaturase. This enzyme catalyzes the conversion of the Δ(12)-double bond of linoleic acid (18:2Δ(9cis,12cis) ) into conjugated Δ(11trans) and Δ(13cis) -double bonds. Previous attempts to produce punicic acid in transgenic Arabidopsis thaliana seeds overexpressing P. granatum FADX resulted in a limited accumulation of punicic acid of up to 4.4 %, accompanied by increased accumulation of oleic acid (18:1∆(9cis) ), suggesting that production of punicic acid in some way inhibits the activity of oleate desaturase (Iwabuchi et al. 2003). In the current study, we applied a new strategy to enhance the production of punicic acid in a high linoleic acid A. thaliana fad3/fae1 mutant background using the combined expression of P. granatum FADX and FAD2. This approach led to the accumulation of punicic acid at the level of 21 % of total fatty acids and restored the natural proportion of oleic acid observed in the A. thaliana fad3/fae1 mutant. In addition, we provide new insights into the high oleate phenotype and describe factors limiting the production of punicic acid in genetically engineered plants.

Arabidopsis Transporter MGT6 Mediates Magnesium Uptake and Is Required for Growth under Magnesium Limitation

Although magnesium (Mg²⁺) is the most abundant divalent cation in plant cells, little is known about the mechanism of Mg²⁺ uptake by plant roots. Here, we report a key function of Magnesium Transport6 (MGT6)/Mitochondrial RNA Splicing2-4 in Mg²⁺ uptake and low-Mg²⁺ tolerance in Arabidopsis thaliana. MGT6 is expressed mainly in plant aerial tissues when Mg²⁺ levels are high in the soil or growth medium. Its expression is highly induced in the roots during Mg²⁺ deficiency, suggesting a role for MGT6 in response to the low-Mg²⁺ status in roots. Silencing of MGT6 in transgenic plants by RNA interference (RNAi) resulted in growth retardation under the low-Mg²⁺ condition, and the phenotype was restored to normal growth after RNAi plants were transferred to Mg²⁺-sufficient medium. RNAi plants contained lower levels of Mg²⁺ compared with wild-type plants under low Mg²⁺ but not under Mg²⁺-sufficient conditions. Further analysis indicated that MGT6 was localized in the plasma membrane and played a key role in Mg²⁺ uptake by roots under Mg²⁺ limitation. We conclude that MGT6 mediates Mg²⁺ uptake in roots and is required for plant adaptation to a low-Mg²⁺ environment.

Transgenic upregulation of the condensed tannin pathway in poplar leads to a dramatic shift in leaf palatability for two tree-feeding Lepidoptera

Transgenic hybrid aspen (Populus tremula x tremuloides) overexpressing the MYB134 tannin regulatory gene show dramatically enhanced condensed tannin (proanthocyanidin) levels, as well as shifts in other phenolic metabolites. A series of insect bioassays with forest tent caterpillars (Malacosoma disstria) and gypsy moth (Lymantria dispar) caterpillars was carried out to determine how this metabolic shift affects food preference and performance of generalist tree-feeding lepidopterans. Both species showed a distinct preference for the high-tannin MYB134 overexpressor plants, and L. dispar performance was enhanced relative to controls. L. dispar reached greater pupal weight and showed reduced time to pupation when reared on the MYB134 overexpressing poplar. These results were unexpected since enhanced condensed tannin levels were predicted to act as feeding deterrents. However, the data may be explained by the observed decrease in the salicinoids (phenolic glycosides) salicortin and tremulacin that accompanied the upregulation of the condensed tannins in the transgenics. We conclude that for these two lepidopteran species, condensed tannin levels are unlikely to be a major determinant of caterpillar food preference or performance. However, our experiments show that overexpression of a single regulatory gene in transgenic aspen can have a significant impact on herbivorous insects.

Protease inhibitor from insect silk-activities of derivatives expressed in vitro and in transgenic potato

Several recombinant derivatives of serine protease inhibitor called silk protease inhibitor 2 (SPI2), which is a silk component in Galleria mellonella (Lepidoptera, Insecta), were prepared in the expression vector Pichia pastoris. Both the native and the recombinant protease inhibitors were highly active against subtilisin and proteinase K. The synthetic SPI2 gene with Ala codon in the P1 position was fused with mGFP-5 to facilitate detection of the transgene and its protein product. A construct of the fusion gene with plant regulatory elements (promoter 35S and terminator OCS) was inserted into the binary vector pRD400. The final construct was introduced into Agrobacterium tumefaciens that was then used for genetic transformation of the potato variety Velox. The transgene expression was monitored with the aid of ELISA employing polyclonal antibody against natural SPI2. In vitro tests showed increased resistance to the late blight Phytophthora infestans in several transformed lines. No effect was seen on the growth, mortality, life span or reproduction of Spodoptera littoralis (Lepidoptera, Insecta) caterpillars, while feeding on transformed potato plants expressing the fusion protein, indicating that the transformed potatoes may be harmless to non-target organisms.

LuFLA1PRO and LuBGAL1PRO promote gene expression in the phloem fibres of flax (Linum usitatissimum)

Cell type-specific promoters were identified that drive gene expression in an industrially important product. To identify flax (Linum usitatissimum) gene promoters, we analyzed the genomic regions upstream of a fasciclin-like arabinogalactan protein (LuFLA1) and a beta-galactosidase (LuBGAL1). Both of these genes encode transcripts that have been found to be highly enriched in tissues bearing phloem fibres. Using a beta-glucuronidase (GUS) reporter construct, we found that a 908-bp genomic sequence upstream of LuFLA1 (LuFLA1PRO) directed GUS expression with high specificity to phloem fibres undergoing secondary cell wall development. The DNA sequence upstream of LuBGAL1 (LuBGAL1PRO) likewise produced GUS staining in phloem fibres with developing secondary walls, as well as in tissues of developing flowers and seed bolls. These data provide further evidence of a specific role for LuFLA1 in phloem fibre development, and demonstrate the utility of LuFLA1PRO and LuBGAL1PRO as tools for biotechnology and further investigations of phloem fibre development.

Improved growth and stress tolerance in the Arabidopsis oxt1 mutant triggered by altered adenine metabolism

Plants perceive and respond to environmental stresses with complex mechanisms that are often associated with the activation of antioxidant defenses. A genetic screen aimed at isolating oxidative stress-tolerant lines of Arabidopsis thaliana has identified oxt1, a line that exhibits improved tolerance to oxidative stress and elevated temperature but displays no apparent deleterious growth effects under non-stress conditions. Oxt1 harbors a mutation that arises from the altered expression of a gene encoding adenine phosphoribosyltransferase (APT1), an enzyme that converts adenine to adenosine monophosphate (AMP), indicating a link between purine metabolism, whole-plant growth responses, and stress acclimation. The oxt1 mutation results in decreased APT1 expression that leads to reduced enzymatic activity. Correspondingly, oxt1 plants possess elevated levels of adenine. Decreased APT enzyme activity directly correlates with stress resistance in transgenic lines that ectopically express APT1. The metabolic alteration in oxt1 plants also alters the expression of several antioxidant defense genes and the response of these genes to oxidative challenge. Finally, it is shown that manipulation of adenine levels can induce stress tolerance to wild-type plants. Collectively, these results show that alterations in cellular adenine levels can trigger stress tolerance and improve growth, leading to increases in plant biomass. The results also suggest that adenine might play a part in the signals that modulate responses to abiotic stress and plant growth.

Expression of nitrous oxide reductase from Pseudomonas stutzeri in transgenic tobacco roots using the root-specific rolD promoter from Agrobacterium rhizogenes

The nitrous oxide (N₂O) reduction pathway from a soil bacterium, Pseudomonas stutzeri, was engineered in plants to reduce N₂O emissions. As a proof of principle, transgenic plants expressing nitrous oxide reductase (N₂OR) from P. stutzeri, encoded by the nosZ gene, and other transgenic plants expressing N₂OR along with the more complete operon from P. stutzeri, encoded by nosFLZDY, were generated. Gene constructs were engineered under the control of a root-specific promoter and with a secretion signal peptide. Expression and rhizosecretion of the transgene protein were achieved, and N₂OR from transgenic Nicotiana tabacum proved functional using the methyl viologen assay. Transgenic plant line 1.10 showed the highest specific activity of 16.7 µmol N₂O reduced min⁻¹ g⁻¹ root protein. Another event, plant line 1.9, also demonstrated high specific activity of N₂OR, 13.2 µmol N₂O reduced min⁻¹ g⁻¹ root protein. The availability now of these transgenic seed stocks may enable canopy studies in field test plots to monitor whole rhizosphere N flux. By incorporating one bacterial gene into genetically modified organism (GMO) crops (e.g., cotton, corn, and soybean) in this way, it may be possible to reduce the atmospheric concentration of N₂O that has continued to increase linearly (about 0.26% year⁻¹) over the past half-century.

RDR1 and SGS3, components of RNA-mediated gene silencing, are required for the regulation of cuticular wax biosynthesis in developing inflorescence stems of Arabidopsis

The cuticle is a protective layer that coats the primary aerial surfaces of land plants and mediates plant interactions with the environment. It is synthesized by epidermal cells and is composed of a cutin polyester matrix that is embedded and covered with cuticular waxes. Recently, we have discovered a novel regulatory mechanism of cuticular wax biosynthesis that involves the ECERIFERUM7 (CER7) ribonuclease, a core subunit of the exosome. We hypothesized that at the onset of wax production, the CER7 ribonuclease degrades an mRNA specifying a repressor of CER3, a wax biosynthetic gene whose protein product is required for wax formation via the decarbonylation pathway. In the absence of this repressor, CER3 is expressed, leading to wax production. To identify the putative repressor of CER3 and to unravel the mechanism of CER7-mediated regulation of wax production, we performed a screen for suppressors of the cer7 mutant. Our screen resulted in the isolation of components of the RNA-silencing machinery, RNA-DEPENDENT RNA POLYMERASE1 and SUPPRESSOR OF GENE SILENCING3, implicating RNA silencing in the control of cuticular wax deposition during inflorescence stem development in Arabidopsis (Arabidopsis thaliana).

Expression of the nos operon proteins from Pseudomonas stutzeri in transgenic plants to assemble nitrous oxide reductase

Nitrous oxide (N(2)O) is a stable greenhouse gas that plays a significant role in the destruction of the ozone layer. Soils are a significant source of atmospheric N(2)O. It is important to explore some innovative and effective biology-based strategies for N(2)O mitigation. The enzyme nitrous oxide reductase (N(2)OR), naturally found in soil bacteria, is responsible for catalysing the final step of the denitrification pathway, conversion of N(2)O to dintrogen gas (N(2)). To transfer this catalytic pathway from soil into plants and amplify the abundance of this essential mechanism (to reduce global warming), a mega-cassette of five coding sequences was assembled to produce transgenic plants heterologously expressing the bacterial nos operon in plant leaves. Both the single-gene transformants (nosZ) and the multi-gene transformants (nosFLZDY) produced active recombinant N(2)OR. Enzymatic activity was detected using the methyl viologen-linked enzyme assay, showing that extracts from both types of transgenic plants exhibited N(2)O-reducing activity. Remarkably, the single-gene strategy produced higher reductase capability than the whole-operon approach. The data indicate that bacterial N(2)OR expressed in plants could convert N(2)O into inert N(2) without involvement of other Nos proteins. Silencing by homologous signal sequences, or cryptic intracellular targeting are possible explanations for the low activities obtained. Expressing N(2)OR from Pseudomonas stutzeri in single-gene transgenic plants indicated that such ag-biotech solutions to climate change have the potential to be easily incorporated into existing genetically modified organism seed germplasm.

Sesbania mosaic virus (SeMV) infectious clone: possible mechanism of 3' and 5' end repair and role of polyprotein processing in viral replication

Sesbania mosaic virus (SeMV) is a positive stranded RNA virus belonging to the genus Sobemovirus. Construction of an infectious clone is an essential step for deciphering the virus gene functions in vivo. Using Agrobacterium based transient expression system we show that SeMV icDNA is infectious on Sesbania grandiflora and Cyamopsis tetragonoloba plants. The efficiency of icDNA infection was found to be significantly high on Cyamopsis plants when compared to that on Sesbania grandiflora. The coat protein could be detected within 6 days post infiltration in the infiltrated leaves. Different species of viral RNA (double stranded and single stranded genomic and subgenomic RNA) could be detected upon northern analysis, suggesting that complete replication had taken place. Based on the analysis of the sequences at the genomic termini of progeny RNA from SeMV icDNA infiltrated leaves and those of its 3' and 5' terminal deletion mutants, we propose a possible mechanism for 3' and 5' end repair in vivo. Mutation of the cleavage sites in the polyproteins encoded by ORF 2 resulted in complete loss of infection by the icDNA, suggesting the importance of correct polyprotein processing at all the four cleavage sites for viral replication. Complementation analysis suggested that ORF 2 gene products can act in trans. However, the trans acting ability of ORF 2 gene products was abolished upon deletion of the N-terminal hydrophobic domain of polyprotein 2a and 2ab, suggesting that these products necessarily function at the replication site, where they are anchored to membranes.

The Arabidopsis calmodulin-like proteins AtCML30 and AtCML3 are targeted to mitochondria and peroxisomes, respectively

Calmodulin (CaM) is a ubiquitous sensor/transducer of calcium signals in eukaryotic organisms. While CaM mediated calcium regulation of cytosolic processes is well established, there is growing evidence for the inclusion of organelles such as chloroplasts, mitochondria and peroxisomes into the calcium/calmodulin regulation network. A number of CaM-binding proteins have been identified in these organelles and processes such as protein import into chloroplasts and mitochondria have been shown to be governed by CaM regulation. What have been missing to date are the mediators of this regulation since no CaM or calmodulin-like protein (CML) has been identified in any of these organelles. Here we show that two Arabidopsis CMLs, AtCML3 and AtCML30, are localized in peroxisomes and mitochondria, respectively. AtCML3 is targeted via an unusual C-terminal PTS1-like tripeptide while AtCML30 utilizes an N-terminal, non-cleavable transit peptide. Both proteins possess the typical structure of CaMs, with two pairs of EF-hand motifs separated by a short linker domain. They furthermore display common characteristics, such as calcium-dependent alteration of gel mobility and calcium-dependent exposure of a hydrophobic surface. This indicates that they can function in a similar manner as canonical CaMs. The presence of close homologues to AtCML3 and AtCML30 in other plants further indicates that organellar targeting of these CMLs is not a specific feature of Arabidopsis. The identification of peroxisomal and mitochondrial CMLs is an important step in the understanding how these organelles are integrated into the cellular calcium/calmodulin signaling pathways.

POPCORN functions in the auxin pathway to regulate embryonic body plan and meristem organization in Arabidopsis

The shoot and root apical meristems (SAM and RAM) formed during embryogenesis are crucial for postembryonic plant development. We report the identification of POPCORN (PCN), a gene required for embryo development and meristem organization in Arabidopsis thaliana. Map-based cloning revealed that PCN encodes a WD-40 protein expressed both during embryo development and postembryonically in the SAM and RAM. The two pcn alleles identified in this study are temperature sensitive, showing defective embryo development when grown at 22°C that is rescued when grown at 29°C. In pcn mutants, meristem-specific expression of WUSCHEL (WUS), CLAVATA3, and WUSCHEL-RELATED HOMEOBOX5 is not maintained; SHOOTMERISTEMLESS, BODENLOS (BDL) and MONOPTEROS (MP) are misexpressed. Several findings link PCN to auxin signaling and meristem function: ectopic expression of DR5(rev):green fluorescent protein (GFP), pBDL:BDL-GFP, and pMP:MP-β-glucuronidase in the meristem; altered polarity and expression of pPIN1:PIN1-GFP in the apical domain of the developing embryo; and resistance to auxin in the pcn mutants. The bdl mutation rescued embryo lethality of pcn, suggesting that improper auxin response is involved in pcn defects. Furthermore, WUS, PINFORMED1, PINOID, and TOPLESS are dosage sensitive in pcn, suggesting functional interaction. Together, our results suggest that PCN functions in the auxin pathway, integrating auxin signaling in the organization and maintenance of the SAM and RAM.

Potyviral VPg enhances viral RNA Translation and inhibits reporter mRNA translation in planta

Viral protein genome-linked (VPg) plays a central role in several stages of potyvirus infection. This study sought to answer questions about the role of Potato virus A (PVA; genus Potyvirus) VPg in viral and host RNA expression. When expressed in Nicotiana benthamiana leaves in trans, a dual role of VPg in translation is observed. It repressed the expression of monocistronic luciferase (luc) mRNA and simultaneously induced a significant upregulation in the expression of both replicating and nonreplicating PVA RNAs. This enhanced viral gene expression was due at least to the 5' untranslated region (UTR) of PVA RNA, eukaryotic initiation factors 4E and iso 4E [eIF4E/eIF(iso)4E], and the presence of a sufficient amount of VPg. Coexpression of VPg with viral RNA increased the viral RNA amount, which was not the case with the monocistronic mRNA. Both mutations at certain lysine residues in PVA VPg and eIF4E/eIF(iso)4E depletion reduced its ability to upregulate the viral RNA expression. These modifications were also involved in VPg-mediated downregulation of monocistronic luc expression. These results suggest that VPg can titrate eIF4Es from capped monocistronic RNAs. Because VPg-mediated enhancement of viral gene expression required eIF4Es, it is possible that VPg directs eIF4Es to promote viral RNA expression. From this study it is evident that VPg can serve as a specific regulator of PVA expression by boosting the viral RNA amounts as well as the accumulation of viral translation products. Such a mechanism could function to protect viral RNA from being degraded and to secure efficient production of coat protein (CP) for virion formation.

Expression and stress tolerance of PR10 genes from Panax ginseng C. A. Meyer

Pathogenesis-related 10 protein families (PgPR10 proteins) from ginseng are reported to have ribonuclease activity, conferring defense-related resistance against various stresses. Homology-based PCR using PgPR10-2 specific primers allowed for the isolation of two additional PgPR10 genes. PgPR10-1 is identical to the previously reported ribonuclease 1, while PgPR10-3 is a newly-discovered protein, suggesting that the PgPR10s are a multi-gene family. Differential organ-specific transcripts of PgPR10-1 and PgPR10-2 in the flower bud and root, respectively, indicate that there are tissue-specific functional roles for this gene family. Overexpression of PgPR10-2 in Arabidopsis conferred longer root length and a tolerant growth phenotype on NaCl-supplemented media. Further changes in transcriptional levels against sets of abiotic stressors suggest similar functional roles of PgPR10-1 in the root and predominantly in the flower organ based on its higher expression levels. Overall, this suggests that the manipulation of PgPR10 genes in plants can be used as valuable tool to enhance its physiological status.

The production of artemisinin precursors in tobacco

Artemisinin, in the form of artemisinin-based combination therapies (ACTs), is currently the most important compound in the treatment of malaria. The current commercial source of artemisinin is Artemisia annua, but this represents a relatively expensive source for supplying the developing world. In this study, the possibility of producing artemisinin in genetically modified plants is investigated, using tobacco as a model. Heterologous expression of A. annua amorphadiene synthase and CYP71AV1 in tobacco led to the accumulation of amorphadiene and artemisinic alcohol, but not artemisinic acid. Additional expression of artemisinic aldehyde Δ11(13) double-bond reductase (DBR2) with or without aldehyde dehydrogenase 1 (ALDH1) led to the additional accumulation dihydroartemisinic alcohol. The above-mentioned results and in vivo metabolic experiments suggest that amorphane sesquiterpenoid aldehydes are formed, but conditions in the transgenic tobacco cells favour reduction to alcohols rather than oxidation to acids. The biochemical and biotechnological significance of these results are discussed.

A comparison of two class 10 pathogenesis-related genes from alfalfa and their activation by multiple stresses and stress-related signaling molecules

A collection of 29 pathogenesis-related 10 (PR10) genes of Medicago sativa and Medicago truncatula showed that they were almost all obtained from cDNA libraries of tissues undergoing abiotic or biotic stresses. The predicted proteins could be divided into two subclasses, PR10.1 and PR10.2, but in silico predicted models of their three-dimensional structures revealed that they could be further divided based on size of the hydrophobic internal cavity and number of β-bulges. A comparison of the expression of two highly similar M. sativa subclass PR10.1 genes, MsPR10.1A and MsPR10.1B, predicted to have similar sized hydrophobic internal cavities, but a different number of β-bulges revealed differences in their expression patterns. MsPR10.1A was induced faster than MsPR10.1B by ABA, ethylene, and X. campestris pv. alfalfae, but slower than MsPR10.1B by harvesting and wounding. Unlike MsPR10.1A, MsPR10.1B expression was induced in non-harvested tissues following harvesting, but was not induced by heat treatment. Histochemical observations of Nicotiana benthamiana transformed with 657 bp of the MsPR10.1A promoter fused to the β-glucuronidase (GUS) gene showed that GUS expression was wound-inducible in leaves, which was consistent with MsPR10.1A expression in alfalfa leaves. GUS expression in stems and leaves was mostly in vascular tissue. The MsPR10.1A promoter may be valuable in controlling the expression in vascular tissues and disease resistance.

The Ca(2+) -dependent protein kinase CPK3 is required for MAPK-independent salt-stress acclimation in Arabidopsis

Plants use different signalling pathways to respond to external stimuli. Intracellular signalling via calcium-dependent protein kinases (CDPKs) or mitogen-activated protein kinases (MAPKs) present two major pathways that are widely used to react to a changing environment. Both CDPK and MAPK pathways are known to be involved in the signalling of abiotic and biotic stresses in animal, yeast and plant cells. Here, we show the essential function of the CDPK CPK3 (At4g23650) for salt stress acclimation in Arabidopsis thaliana, and test crosstalk between CPK3 and the major salt-stress activated MAPKs MPK4 and MPK6 in the salt stress response. CPK3 kinase activity was induced by salt and other stresses after transient overexpression in Arabidopsis protoplasts, but endogenous CPK3 appeared to be constitutively active in roots and leaves in a strictly Ca(2+) -dependent manner. cpk3 mutants show a salt-sensitive phenotype comparable with mutants in MAPK pathways. In contrast to animal cells, where crosstalk between Ca(2+) and MAPK signalling is well established, CPK3 seems to act independently of those pathways. Salt-induced transcriptional induction of known salt stress-regulated and MAPK-dependent marker genes was not altered, whereas post-translational protein phosphorylation patterns from roots of wild type and cpk3 plants revealed clear differences. A significant portion of CPK3 was found to be associated with the plasma membrane and the vacuole, both depending on its N-terminal myristoylation. An initial proteomic study led to the identification of 28 potential CPK3 targets, predominantly membrane-associated proteins.

Renilla luciferase-based quantitation of Potato virus A infection initiated with Agrobacterium infiltration of N. benthamiana leaves

A quantitation method based on the sensitive detection of Renilla luciferase (Rluc) activity was developed and optimized for Potato virus A (PVA; genus Potyviridae) gene expression. This system is based on infections initiated by Agrobacterium infiltration and subsequent detection of the translation of PVA::Rluc RNA, which is enhanced by viral replication, first within the cells infected initially and later by translation and replication within new cells after spread of the virus. Firefly luciferase (Fluc) was used as an internal control to normalize the Rluc activity. An approximately 10-fold difference in the Rluc/Fluc activity ratio between a movement-deficient and a replication-deficient mutant was observed starting from 48h post Agrobacterium infiltration (h.p.i.). The Rluc activity derived from wild type (wt) PVA increased significantly between 48 and 72h.p.i. and the Rluc/Fluc activity deviated clearly from that of the mutant viruses. Quantitation of the Rluc and Fluc mRNAs by semi-quantitative RT-PCR indicated that increases and decreases in the Renillareniformis luciferase (rluc) mRNA levels coincided with changes in Rluc activity. However, a subtle increase in the mRNA level led to pronounced changes in Rluc activity. PVA CP accumulation was quantitated by enzyme-linked immunosorbent assay. The increase in Rluc activity correlated closely with virus accumulation.

Expression of Cry1Ac in transgenic tobacco plants under the control of a wound-inducible promoter (AoPR1) isolated from Asparagus officinalis to control Heliothis virescens and Manduca sexta

Expression of cry1Ac gene from Bacillus thuringiensis (Bt) was evaluated under the control of a wound-inducible AoPR1 promoter from Asparagus officinalis in transgenic tobacco plants. The leaves of transgenic plants were mechanically wounded to evaluate the activity of the AoPR1 promoter in driving the expression of Cry1Ac protein at the wound site. Our results indicate that mechanical wounding of transgenic plants was effective in inducing the expression of Cry1Ac protein. As a result of this induction, the accumulated levels of Cry1Ac protein increased during 6-72 h post-wounding period. The leaves of transgenic tobacco plants were evaluated for resistance against Heliothis virescens and Manduca sexta in insect bioassays in two different ways. The detached tobacco leaves were either fed directly to the insect larvae or they were first mechanically wounded followed by a 72 h post-wounding feeding period. Complete protection of mechanically wounded leaves of transgenic plants was observed within 24 h of the bioassay. The leaves of transgenic plants fed directly (without pre-wounding) to the larvae achieved the same level of protection between 24 and 72 h of the bioassay.

A mitogen-activated protein kinase gene, AhMPK3 of peanut: molecular cloning, genomic organization, and heterologous expression conferring resistance against Spodoptera litura in tobacco

Mitogen-activated protein kinase cascade plays a very important role in plant signal transduction mechanism. A full length cDNA of 1,514 bp length, corresponding to a mitogen-activated protein kinase gene was cloned from peanut (Arachis hypogaea). Based on its high homology with Arabidopsis AtMPK3, the cDNA was designated as AhMPK3. It carried an open reading frame of 1,113 bp encoding a 371 amino acid polypeptide. AhMPK3 bears TEY motif in its activation loop and belongs to the A1 subgroup of MAPK family. Southern blot analysis revealed that AhMPK3 exists in two copies in peanut genome and its structural organization revealed well-conserved nature of these signaling components across different species. AhMPK3 when transiently expressed in tobacco leaves was found to localize in both nucleus and cytoplasm. Transgenic tobacco plants ectopically expressing AhMPK3 exhibited enhanced resistance to first and second instar larvae of Spodoptera litura and constitutively higher transcript levels of defense response genes like PR1a, PR1b, LOX1, PI-II etc. Apart from this when wounded, transgenic plants accumulated high levels of PI-II and PR1b transcripts rapidly compared to wild type indicating the occurrence of a priming phenomenon.

The wound-, pathogen-, and ultraviolet B-responsive MYB134 gene encodes an R2R3 MYB transcription factor that regulates proanthocyanidin synthesis in poplar

In poplar (Populus spp.), the major defense phenolics produced in leaves are the flavonoid-derived proanthocyanidins (PAs) and the salicin-based phenolic glycosides. Transcriptional activation of PA biosynthetic genes leading to PA accumulation in leaves occurs following herbivore damage and mechanical wounding as well as infection by the fungal biotroph Melampsora medusae. In this study, we have identified a poplar R2R3 MYB transcription factor gene, MYB134, that exhibits close sequence similarity to the Arabidopsis (Arabidopsis thaliana) PA regulator TRANSPARENT TESTA2 and that is coinduced with PA biosynthetic genes following mechanical wounding, M. medusae infection, and exposure to elevated ultraviolet B light. Overexpression of MYB134 in poplar resulted in transcriptional activation of the full PA biosynthetic pathway and a significant plant-wide increase in PA levels, and electrophoretic mobility shift assays showed that recombinant MYB134 protein is able to bind to promoter regions of PA pathway genes. MYB134-overexpressing plants exhibited a concomitant reduction in phenolic glycoside concentrations and other minor alterations to levels of small phenylpropanoid metabolites. Our data provide insight into the regulatory mechanisms controlling stress-induced PA metabolism in poplar, and the identification of a regulator of stress-responsive PA biosynthesis constitutes a valuable tool for manipulating PA metabolism in poplar and investigating the biological functions of PAs in resistance to biotic and abiotic stresses.

A mitochondrial magnesium transporter functions in Arabidopsis pollen development

Magnesium is an abundant divalent cation in plant cells and plays a critical role in many physiological processes. We have previously described the identification of a 10-member Arabidopsis gene family encoding putative magnesium transport (MGT) proteins. Here, we report that a member of the MGT family, AtMGT5, functions as a dual-functional Mg-transporter that operates in a concentration-dependent manner, namely it serves as a Mg-importer at micromolar levels and facilitates the efflux in the millimolar range. The AtMGT5 protein is localized in the mitochondria, suggesting that AtMGT5 mediates Mg-trafficking between the cytosol and mitochondria. The AtMGT5 gene was exclusively expressed in anthers at early stages of flower development. Examination of two independent T-DNA insertional mutants of AtMGT5 gene demonstrated that AtMGT5 played an essential role for pollen development and male fertility. This study suggests a critical role for Mg(2+) transport between cytosol and mitochondria in male gametogenesis in plants.

Comparative genomic sequence and expression analyses of Medicago truncatula and alfalfa subspecies falcata COLD-ACCLIMATION-SPECIFIC genes

In Arabidopsis (Arabidopsis thaliana) the low-temperature induction of genes encoding the C-REPEAT BINDING FACTOR (CBF) transcriptional activators is a key step in cold acclimation. CBFs in turn activate a battery of downstream genes known as the CBF regulon, which collectively act to increase tolerance to low temperatures. Fundamental questions are: What determines the size and scope of the CBF regulon, and is this is a major determinant of the low-temperature tolerance capacity of individual plant species? Here we have begun to address these questions through comparative analyses of Medicago truncatula and Medicago sativa subsp. falcata. M. truncatula survived to -4 degrees C but did not cold acclimate, whereas Medicago falcata cold acclimated and survived -14 degrees C. Both species possessed low-temperature-induced CBFs but differed in the expression of the COLD-ACCLIMATION-SPECIFIC (CAS) genes, which are candidate CBF targets. M. falcata CAS30 was robustly cold-responsive whereas the MtCAS31 homolog was not. M. falcata also possessed additional CAS30 homologs in comparison to the single CAS31 gene in M. truncatula. MfCAS30 possessed multiple pairs of closely spaced C-REPEAT/DEHYDRATION RESPONSIVE ELEMENT (CRT/DRE) motifs, the cognate CBF binding site in its upstream region whereas MtCAS31 lacked one CRT/DRE partner of the two proximal partner pairs. CAS genes also shared a promoter structure comprising modules proximal and distal to the coding sequence. CAS15, highly cold-responsive in both species, harbored numerous CRT/DRE motifs, but only in the distal module. However, fusion of the MtCAS15 promoter, including the distal module, to a reporter gene did not result in low-temperature responsiveness in stably transformed Arabidopsis. In contrast, both MtCAS31 and MfCAS30 promoter fusions were low-temperature responsive, although the MfCAS31 fusion was less robust than the MfCAS30 fusion. From these studies we conclude that CAS genes harbor CRT/DRE motifs, their proximity to one another is likely key to regulatory output in Medicago, and they may be located kilobases distal to the transcriptional start site. We hypothesize that these differences in CRT/DRE copy numbers in CAS30/CAS31 upstream regions combined with differences in gene copy numbers may be a factor in determining differences in low-temperature tolerance between M. truncatula and M. falcata.

A human anti-Pseudomonas aeruginosa serotype O6ad immunoglobulin G1 expressed in transgenic tobacco is capable of recruiting immune system effector function in vitro

The production of a recombinant human IgG1 in transgenic tobacco was examined to determine whether a plant-derived antibody could recruit immune system effector function against a bacterial pathogen. A plant transformation vector was engineered to contain genes for a human kappa light chain and a human gamma-1 heavy chain with V(H) and V(L) sequences from a previously identified human IgG2 monoclonal antibody (MAb) that specifically binds to and opsonizes Pseudomonas aeruginosa serotype O6ad. Unique NcoI and NotI restriction sites were incorporated to flank these variable sequences, resulting in a plant transformation vector that could be engineered for expression of any other human IgG1 antibody, requiring only the substitution of other V(H) and V(L) antigen-binding coding sequences. The plant-produced IgG1 was determined to have high-mannose glycan content and to be capable of mediating opsonophagocytosis of P. aeruginosa serotype O6ad in vitro using human complement and human polymorphonuclear leukocytes. Thus, MAbs produced in plants from this vector could provide human IgG1 MAbs for targeting other pathogens that require the recruitment of immune system effector functions.

CER4 encodes an alcohol-forming fatty acyl-coenzyme A reductase involved in cuticular wax production in Arabidopsis

A waxy cuticle that serves as a protective barrier against uncontrolled water loss and environmental damage coats the aerial surfaces of land plants. It is composed of a cutin polymer matrix and waxes. Cuticular waxes are complex mixtures of very-long-chain fatty acids and their derivatives. We report here the molecular cloning and characterization of CER4, a wax biosynthetic gene from Arabidopsis (Arabidopsis thaliana). Arabidopsis cer4 mutants exhibit major decreases in stem primary alcohols and wax esters, and slightly elevated levels of aldehydes, alkanes, secondary alcohols, and ketones. This phenotype suggested that CER4 encoded an alcohol-forming fatty acyl-coenzyme A reductase (FAR). We identified eight FAR-like genes in Arabidopsis that are highly related to an alcohol-forming FAR expressed in seeds of jojoba (Simmondsia chinensis). Molecular characterization of CER4 alleles and genomic complementation revealed that one of these eight genes, At4g33790, encoded the FAR required for cuticular wax production. Expression of CER4 cDNA in yeast (Saccharomyces cerevisiae) resulted in the accumulation of C24:0 and C26:0 primary alcohols. Fully functional green fluorescent protein-tagged CER4 protein was localized to the endoplasmic reticulum in yeast cells by confocal microscopy. Analysis of gene expression by reverse transcription-PCR indicated that CER4 was expressed in leaves, stems, flowers, siliques, and roots. Expression of a beta-glucuronidase reporter gene driven by the CER4 promoter in transgenic plants was detected in epidermal cells of leaves and stems, consistent with a dedicated role for CER4 in cuticular wax biosynthesis. CER4 was also expressed in all cell types in the elongation zone of young roots. These data indicate that CER4 is an alcohol-forming FAR that has specificity for very-long-chain fatty acids and is responsible for the synthesis of primary alcohols in the epidermal cells of aerial tissues and in roots.

Human CD14 expressed in seeds of transgenic tobacco displays similar proteolytic resistance and bioactivity with its mammalian-produced counterpart

Human CD14 plays an important role in innate immunity by being the key receptor of lipopolysaccharide found on Gram-negative bacteria. The recently discovered widespread localization of CD14 in secretions and mucosal surfaces reveals its extensive anti-microbial properties and numerous potential medical applications. To produce active recombinant human CD14 (rhCD14) for massive distribution, transgenic tobacco plants were successfully generated to express rhCD14 in the seed endosperm under the control of two versions (1.8 kb and 5.1 kb) of the rice glutelin Gt-1 promoter. Plant-made rhCD14 proteins reached a concentration of 16 microg/g of seeds and showed stability, proteolytic resistance to pepsin digestion and ability to induce the release of pro-inflammatory IL-6 and IL-8 cytokines in presence of LPS. The expression of plant rhCD14 in tobacco seeds constitutes a promising low-cost and abundant supply of this immune protein to further investigate its roles in, impacts on and potential medical applications for the innate immune system.

Expression of 1-aminocyclopropane-1-carboxylate (ACC) oxidase genes during the development of vegetative tissues in white clover (Trifolium repens L.) is regulated by ontological cues

Four 5' flanking sequences, comprising the 5'-UTR and upstream promoter region, have been isolated and cloned from the 1-aminocyclopropane-1-carboxylate (ACC) oxidase gene family of white clover (Trifolium repens L.), and designated TR-ACO1p, TR-ACO2p, TR-ACO3p and TR-ACO4p. Southern analysis confirmed that these sequences correspond to four distinct genes. The four corresponding genomic sequences have also been isolated and each shown to be comprised of four exons interspersed by three introns. The expression pattern, in vivo, directed by all four 5' flanking sequences during leaf development has been examined using GUS fusions and transformation into white clover. Here, the TR-ACO1 5' flanking sequence directs highest expression in the apical tissues, axillary buds, and leaf petiolules in younger tissues and then declines in the ageing tissues, while the TR-ACO2 5' flanking sequence directs expression in both younger, mature green and in ontologically ageing tissue. The TR-ACO3 and TR-ACO4 5' flanking sequences direct more expression in the ontological older tissues, including the axillary buds and leaf petiolules. The TR-ACO1 5' flanking sequence directed expression in the ground meristem and newly emerged leaf tissue at the apical bud of the stolon, but all four 5' flanking sequences directed expression in the ground meristem tissue of axillary buds, vascular tissue, pith and cortex of the internode and node, and the cortex and vascular tissue of the leaf petiolule, with the primacy of each promoter determined by the ontological age of the tissues. These data suggest that in vegetative tissue development of white clover, the primary cues for the transcriptional regulation of the ACO gene family are ontological in nature.

A multifunctional acyl-acyl carrier protein desaturase from Hedera helix L. (English ivy) can synthesize 16- and 18-carbon monoene and diene products

A desaturase with 83% sequence identity to the coriander delta(4)-16:0-ACP desaturase was isolated from developing seeds of Hedera helix (English ivy). Expression of the ivy desaturase in Arabidopsis resulted in the accumulation of 16:1delta(4) and its expected elongation product 18:1delta(6) (petroselinic acid). Expression in Escherichia coli resulted in the accumulation of soluble, active protein that was purified to apparent homogeneity. In vitro assays confirmed delta(4) desaturation with 16:0-ACP; however, with 18:0-acyl acyl carrier protein (ACP) desaturation occurred at the delta(9) position. The ivy desaturase also converted 16:1delta(9)-ACP and 18:1delta(9)-ACP to the corresponding delta(4,9) dienes. These data suggest at least two distinct substrate binding modes, one placing C4 at the diiron active site and the other placing C9 at the active site. In the latter case, 18:0 would likely bind in an extended conformation as described for the castor desaturase with 9-carbons accommodated in the cavity beyond the dirron site. However, delta(4) desaturation would require the accommodation of 12 carbons for C16 substrates or 14 carbons for C18 substrates. The amino acids lining the substrate binding cavity of ivy and castor desaturases are conserved except for T117R and P179I (castor/ivy). Paradoxically, both substitutions, when introduced into the castor desaturase, favored the binding of shorter acyl chains. Thus, it seems likely that delta(4) desaturation would require a non-extended, perhaps U-shaped, substrate conformation. A cis double bond may facilitate the initiation of such a non-extended conformation in the monounsaturated substrates. The multifunctional properties of the ivy desaturase make it well suited for further dissection of the determinants of regiospecificity.

The Bt gene cry2Aa2 driven by a tissue specific ST-LS1 promoter from potato effectively controls Heliothis virescens

Expression of the Cry2Aa2 protein was targeted specifically to the green tissues of transgenic tobacco Nicotiana tabacum cv. Xanthi plants. This deployment was achieved by using the promoter region of the gene encoding the Solanum tuberosum leaf and stem specific (ST-LS1) protein. The accumulated levels of toxin in the leaves were found to be effective in achieving 100% mortality of Heliothis virescens larvae. The levels of Cry2Aa2 expression in the leaves of these transgenic plants were up to 0.21% of the total soluble proteins. Bioassays with R1 transgenic plants indicated the inheritance of cry2Aa2 in the progeny plants. Tissue-specific expression of the Bt toxin in transgenic plants may help in controlling the potential occurrence of insect resistance by limiting the amount of toxin to only predated tissues. The results reported here validate the use of the ST-LS1 gene promoter for a targeted expression of Bt toxins in green tissues of plants.

Cell-specific regulation of a Brassica napus CMS-associated gene by a nuclear restorer with related effects on a floral homeotic gene promoter

Cytoplasmic male sterility (CMS) is a maternally inherited defect in pollen production specified by novel mitochondrial genes. It can be suppressed by nuclear restorer (Rf) genes which normally downregulate expression of a CMS-associated novel mitochondrial gene. Two forms of Brassica napus CMS, nap and pol, are associated with related chimeric genes, orf222 and orf224, respectively. We show that in pol and nap CMS, anther locule development is asynchronous and asymmetric, that one or more locules within each anther may fail to develop entirely and that CMS anthers display polarity in locule development. We show, by in situ hybridization, that orf222 transcripts accumulate in sterile anthers prior to development of morphological differences between CMS and restored stamens, and remain preferentially localized to microsporangia. In fertility-restored anthers, however, orf222 transcript levels remain low throughout development. Some sporogenous and meiotic cells differentiate within CMS anthers and form functional pollen despite retaining high orf222 transcript levels, suggesting that the effect of orf222 expression in blocking pollen development is limited to an early and specific stage. Transcripts of other mitochondrial genes, exemplified by atp6 and cob, and of the nuclear-encoded ATP synthase gamma subunit, accumulate preferentially in the microsporangia of both sterile and fertile anthers. Thus nuclear fertility restoration reduces orf222 transcript levels in a gene and tissue-specific manner. We observe differences between CMS and fertile plants in the timing and patterning of APETALA3 promoter activity that suggest a possible basis for the developmental abnormalities of CMS flowers.

Polyphenol oxidase overexpression in transgenic Populus enhances resistance to herbivory by forest tent caterpillar (Malacosoma disstria)

In order to functionally analyze the predicted defensive role of leaf polyphenol oxidase (PPO; EC 1.10.3.1) in Populus, transgenic hybrid aspen (Populus tremula x P. alba) plants overexpressing a hybrid poplar (Populus trichocarpa x P. deltoides) PtdPPO1 gene were constructed. Regenerated transgenic plants showed high PPO enzyme activity, PtdPPO1 mRNA levels and PPO protein accumulation. In leaf disk bioassays, forest tent caterpillar (Malacosoma disstria) larvae feeding on PPO-overexpressing transgenics experienced significantly higher mortality and reduced average weight gain compared to larvae feeding on control leaves. However, this effect was observed only when older egg masses were used and the resulting larvae showed reduced growth and vigor. In choice tests, no effect of PPO overexpression was detected. Although PPO in poplar leaves is latent and requires activation with detergents or trypsin for full enzymatic activity, in caterpillar frass the enzyme was extracted in the fully activated form. This activation correlated with partial proteolytic cleavage, suggesting that PPO latency and activation during digestion could be an adaptive and defense-related feature of poplar PPO.

Transgenic tobacco cells producing the human monoclonal antibody to hepatitis B virus surface antigen

The recombinant human monoclonal antibody (MAb) against hepatitis B virus (HBV) surface antigen (HBsAg) was expressed in tobacco suspension cultures. The parental CL4MAb was produced by the Epstein-Barr virus (EBV) transformed human cell line TAPC301-CL4. The CL4MAb cDNA was introduced into tobacco suspension cells by Agrobacterium mediated transformation. The monoclonal antibodies (MAbs), B294 and B303, which were derived from CL4 and subsequently produced in plant cells were selected for study. After purification on Protein A columns, B294 and B303 MAbs had anti-HBs relative affinity constants similar to the parental CL4MAb. B303 MAb interacted with cell surface HBsAgs and showed complement-dependent cytotoxicity in a manner that was similar to anti-HBs human immunoglobulins (HBIg) that are used clinically. The results of this study point to the feasibility of producing MAbs to HBsAg in plants as an alternative to HBIg.

Transgenic tobacco and apple plants expressing biotin-binding proteins are resistant to two cosmopolitan insect pests, potato tuber moth and lightbrown apple moth, respectively

Tobacco (Nicotiana tabacum cv. Samsun) and apple (Malus x domestica cv. Royal Gala) plants expressing avidin or strepavidin were produced using Agrobacterium tumefaciens-mediated transformation. ELISA assays showed that avidin expression ranged from 3.1 to 4.6 microM in tobacco and from 1.9 to 11.2 microM in apple and streptavidin expression ranged from 11.4 to 24.5 microM in tobacco and from 0.4 to 14.6 microM in apple. Expressed at these levels, both biotin-binding proteins conferred a high level of insect resistance on transformed tobacco plants to larval potato tuber moth (PTM), Phthorimaea operculella (Zeller) (fam. Gelechiidae) and on apple plants to larvae of the lightbrown apple moth (LBAM) Epiphyas postvittana (Walker) (fam. Tortricidae). More than 90% of PTM larvae died on tobacco plants expressing either avidin or streptavidin genes within 9 days of inoculation. Mortality of LBAM larvae was significantly higher (P < 0.05) on three avidin-expressing (89.6, 84.9 and 80.1%) and two streptavidin-expressing (90 and 82.5%) apple plant lines than on non-transformed control plants (14.1%) after 21 days. Weight of LBAM larvae was also significantly reduced by feeding on all apple shoots expressing avidin and on apple shoots expressing streptavidin at levels of 3.8 microM and above.

The radish Rfo restorer gene of Ogura cytoplasmic male sterility encodes a protein with multiple pentatricopeptide repeats

A single radish nuclear gene, Rfo, restores Ogura (ogu) cytoplasmic male sterility (CMS) in Brassica napus. A map-based cloning approach relying on synteny between radish and Arabidopsis was used to clone Rfo. A radish gene encoding a 687-amino-acid protein with a predicted mitochondrial targeting pre-sequence was found to confer male fertility upon transformation into ogu CMS B. napus. This gene, like the recently described Petunia Rf gene, codes for a pentatricopeptide repeat (PPR)-containing protein with multiple, in this case 16, PPR domains. Two similar genes that do not appear to function as Rfo flank this gene. Comparison of the Rfo region with the syntenic Arabidopsis region indicates that a PPR gene is not present at the Rfo-equivalent site in Arabidopsis, although a smaller and related PPR gene is found about 40 kb from this site. The implications of these findings for the evolution of restorer genes and other PPR encoding genes are discussed.

Increased yield of heterologous viral glycoprotein in the seeds of homozygous transgenic tobacco plants cultivated underground

The use of transgenic plants in the production of recombinant proteins for human therapy, including subunit vaccines, is being investigated to evaluate the efficacy and safety of these emerging biopharmaceutical products. We have previously shown that synthesis of recombinant glycoprotein B (gB) of human cytomegalovirus can be targeted to seeds of transgenic tobacco when directed by the rice glutelin 3 promoter, with gB retaining critical features of immunological reactivity (E.S. Tackaberry et al. 1999. Vaccine, 17: 3020-3029). Here, we report development of second generation transgenic plant lines (T1) homozygous for the transgene. Twenty progeny plants from two lines (A23T(1)-2 and A24T(1)-3) were grown underground in an environmentally contained mine shaft. Based on yields of gB in their seeds, the A23T(1)-2 line was then selected for scale-up in the same facility. Analyses of mature seeds by ELISA showedthat gB specific activity in A23T(1)-2 seeds was over 30-fold greater than the best T0 plants from the same transformation series, representing 1.07% total seed protein. These data demonstrate stable inheritance, an absence of transgene inactivation, and enhanced levels of gB expression in a homozygous second generation plant line. They also provide evidence for the suitability of using this environmentally secure facility to grow transgenic plants producing therapeutic biopharmaceuticals.