In planta transformation of Arabidopsis thaliana

Transformants of Arabidopsis thaliana can be generated without using tissue culture techniques by cutting primary and secondary inflorescence shoots at their bases and inoculating the wound sites with Agrobacterium tumefaciens suspensions. After three successive inoculations, treated plants are grown to maturity, harvested and the progeny screened for transformants on a selective medium. We have investigated the reproducibility and the overall efficiency of this simple in planta transformation procedure. In addition, we determined the T-DNA copy number and inheritance in the transformants and examined whether transformed progeny recovered from the same Agrobacterium-treated plant represent one or several independent transformation events. Our results indicate that in planta transformation is very reproducible and yields stably transformed seeds in 7–8 weeks. Since it does not employ tissue culture, the in planta procedure may be particularly valuable for transformation of A. thaliana ecotypes and mutants recalcitrant to in vitro regeneration. The transformation frequency was variable and was not affected by lower growth temperature, shorter photoperiod or transformation vector. The majority of treated plants gave rise to only one transformant, but up to nine siblings were obtained from a single parental plant. Molecular analysis suggested that some of the siblings originated from a single transformed cell, while others were descended from multiple, independently transformed germ-line cells. More than 90% of the transformed progeny exhibited Mendelian segregation patterns of NPTII and GUS reporter genes. Of those, 60% contained one functional insert, 16% had two T-DNA inserts and 15% segregated for T-DNA inserts at more than two unlinked loci. The remaining transformants displayed non-Mendelian segregation ratios with a very high proportion of sensitive plants among the progeny. The small numbers of transformants recovered from individual T₁ plants and the fact that none of the T₂ progeny were homozygous for a specific T-DNA insert suggest that transformation occurs late in floral development.     

Stable genetic transformation of Arabidopsis thaliana by Agrobacterium inoculation in planta

Stable genetic transformation of Arabidopsis thaliana was achieved by simple in planta inoculation of Agrobacterium tumefaciens strain LBA4404 harboring a binary vector pBl121. The transformation procedure, which we call in planta transformation, involves severing of apical shoots at their bases, inoculation with Agrobacterium at the severed sites, and in planta generation of shoots from the severed sites. On average, 5.5% of the newly formed shoots produced transformed progenies. These progenies (T₂ generation) contained T-DNA in the genome as examined by assaying the T-DNA encoded β-glucuronidase and kanamycin resistance and by genomic Southern blot analysis, the copy number of the T-DNAs in the Arabidopsis genome being single (33%) or multiple. The genetic behavior of the transformants examined at the T₃ and T₄ generations or with the F₂ progenies of the outcrosses between transformants and wild-type plants showed that most of the inserted T-DNA are inherited in a Mendelian fashion. This procedure provides a new approach for simple and efficient transformation of A. thaliana, obviating the need for plant regeneration from tissue explants in vitro.     

Identification of Alternaria brassicicola genes expressed in planta during pathogenesis of Arabidopsis thaliana

Alternaria brassicicola is a necrotrophic fungal pathogen that causes black spot disease on cruciferous plants including economically important Brassica species. The purpose of this study was to identify fungal genes expressed during infection of Arabidopsis. In order to identify candidate genes involved in pathogenicity, we employed suppression subtractive hybridization (SSH) between RNA isolated from A. brassicicola spores incubated in water and on the leaf surface of the Arabidopsis ecotype Landsberg. Two populations of cDNA were created from total RNA extracted after 24h when approximately 80% of the spores had germinated either on the leaf surface or in water. Following SSH, expression of clones was examined using dot-blot macro-arrays and virtual Northern blots. 47 cDNA clones differentially expressed between Alternaria infected Arabidopsis leaves and spore germination in water were selected for sequencing. Seventy-seven percent (36) of the cDNAs had significant homology to fungal sequences from databases examined, including available fungal genomes, while 13% (11) had no homology to sequences in the databases. All 36 genes had significant matches with genes of fungal origin, while 11 genes did not have significant hits in the databases examined. Five sequences were expressed on the plant leaf surface but not during spore germination in water according to virtual Northern blots. These five cDNAs were predicted to encode a cyanide hydratase, arsenic ATPase, formate dehydrogenase, major Alternaria allergen, and one unknown. RT-PCR was used to examine the expression of these five genes during infection of Brassica oleraceae var. capitata (cabbage), in vitro growth in nutrient rich media, and infection of Arabidopsis thaliana. Four of these genes are expressed in the nutrient rich medium, while the unknown gene P3F2 was only expressed during plant infection. The results of this study provide the first insight into genes expressed during A. brassicicola infection of Brassica species that may be involved in fungal pathogenesis.     

The longin domain regulates subcellular targeting of VAMP7 in Arabidopsis thaliana

SNAREs (soluble N-ethyl-maleimide sensitive factor attachment protein receptors) which locate on the specific organelle membrane assure the correct vesicular transport by mediating specific membrane fusions. SNAREs are referred to as R- or Q-SNAREs on the basis of the amino acid sequence similarities and specific conserved residues. All of the Arabidopsis R-SNAREs have a N-terminal domain, called the longin domain (LD). In this study, we investigated the vacuolar targeting mechanism of Arabidopsis R-SNAREs. The vacuolar localized AtVAMP711 was used as the mother protein of GFP-tagged chimeric proteins joined to several domains such as the LD, the SNARE motif (SNM) and the transmembrane domain (TMD) of other organelle-localized R-SNAREs. The results showed that, whereas the TMD is not relevant for the vacuolar targeting, a complete LD is essential for the vacuolar and subcellular targeting.     

Hydrogen peroxide-induced gene expression in Arabidopsis thaliana

Hydrogen peroxide (H(2)O(2)) is generated in plants after exposure to a variety of biotic and abiotic stresses, and has been shown to induce a number of cellular responses. Previously, we showed that H(2)O(2) generated during plant-elicitor interactions acts as a signaling molecule to induce the expression of defense genes and initiate programmed cell death in Arabidopsis thaliana suspension cultures. Here, we report for the first time the identification by RNA differential display of four genes whose expression is induced by H(2)O(2). These include genes that have sequence homology to previously identified Arabidopsis genes encoding a late embryogenesis-abundant protein, a DNA-damage repair protein, and a serine/threonine kinase. Their putative roles in H(2)O(2)-induced defense responses are discussed.     

An expression atlas of miRNAs in Arabidopsis thaliana

MicroRNAs(miRNAs) are small non-coding RNAs that regulate a variety of biological processes. miRNA expression often exhibits spatial and temporal specificity. However, genome-wide miRNA expression patterns in different organs during development of Arabidopsis thaliana have not yet been systemically investigated. In this study, we sequenced small RNA libraries generated from 27 different organ/tissue types, which cover the entire life cycle of Arabidopsis. Analysis of the sequencing data revealed that most miRNAs are ubiquitously expressed, whereas a small set of miRNAs display highly specific expression patterns. In addition, different miRNA members within the same family have distinct spatial and temporal expression patterns. Moreover, we found that some miRNAs are produced from different arms of their hairpin precursors at different developmental stages. This work provides new insights into the regulation of miRNA biogenesis and a rich resource for future investigation of miRNA functions in Arabidopsis.     

Identification and subcellular localization of two solanesyl diphosphate synthases from Arabidopsis thaliana

Two solanesyl diphosphate synthases, designated SPS1 and SPS2, which are responsible for the synthesis of the isoprenoid side chain of either plastoquinone or ubiquinone in Arabidopsis thaliana, were identified. Heterologous expression of either SPS1 or SPS2 allowed the generation of UQ-9 in a decaprenyl diphosphate synthase-defective strain of fission yeast and also in wild-type Escherichia coli. SPS1-GFP was found to localize in the ER while SPS2-GFP localized in the plastid of tobacco BY-2 cells. These two different subcellular localizations are thought to be the reflection of their roles in solanesyl diphosphate synthesis in two different parts: presumably SPS1 and SPS2 for the side chains of ubiquinone and plastoquinone, respectively.     

Protein expression in Arabidopsis thaliana after chronic clinorotation

Soluble protein expression in Arabidopsis thaliana L. (Heynh.) leaf and stem tissue was examined after chronic clinorotation. Seeds of Arabidopsis were germinated and plants grown to maturity on horizontal or vertical slow-rotating clinostats (1 rpm) or in stationary vertical control units. Total soluble proteins and in vivo-labeled soluble proteins isolated from these plants were analyzed by two-dimensional SDS PAGE and subsequent fluorography. Visual and computer analysis of the resulting protein patterns showed no significant differences in either total protein expression or in active protein synthesis between horizontal clinorotation and vertical controls in the Arabidopsis leaf and stem tissue. These results show chronic clinorotation does not cause gross changes in protein expression in Arabidopsis.     

Future of early embryogenesis studies in Arabidopsis thaliana.

Embryogenesis is a long-standing field of interest for plant scientist as recorded in the 'notes' of the French Science Academy. This either with fundamental or applied points of view. Since the beginning of the century techniques and questions have co-evolved, from microscope and fate map to laser ablation and cell-cell signalling. So far in plant embryogenesis, a limited use has been made of the whole range of approaches generally available to study development. This is due to technical limitations when working with plant embryos. Novel mutant screens and techniques are now at hand and are expected to unravel further the nature of cell interactions underlying embryo development. This in turn will modify the focus of our questioning.     

Identification,sequence analysis and expression studies of novel anther-specific genes of Arabidopsis thaliana

Relatively little is known about pollen development at the molecular level. For the purpose of gaining understanding of the molecular control of pollen development, a number of Arabidopsis cDNA fragments were isolated using subtractive hybridizations. DNA and RNA hybridizations and sequence analyses indicate that we have isolated cDNAs representing 13 genes. Sequences for 8 of these genes are novel, while those for the remaining 5 genes have substantial similarity to genes previously reported as anther- or pollen-specific. RNA in situ hybridizations with 5 genes revealed that four of them are tapetum-specific with differing temporal expression patterns during pollen development and one is pollen-specific within the flower. Sequence analysis of full-length cDNAs showed that one of the novel genes, ATA7, encodes a protein related to lipid transfer proteins. Another gene, ATA20, encodes a protein with novel repeat sequences and a glycine-rich domain that shares a predicted structure with a known cell wall protein. The full-length ATA27 cDNA encodes a protein similar to the BGL4 -glucosidase from Brassica napus. The ATA27 protein is predicted to have an ER retention signal and an acidic isoelectric point, suggesting that it may be localized to the ER lumen. This may be a means of compartmentalization from its substrate(s). Our studies demonstrate that subtractive hybridizations can be used to identify previously unknown genes, which should be valuable tools for further study of pollen and anther development and function.     

Sugar-inducible expression of a gene for beta-amylase in Arabidopsis thaliana.

The levels of beta-amylase activity and of the mRNA for beta-amylase in rosette leaves of Arabidopsis thaliana (L.) Heynh. increased significantly, with the concomitant accumulation of starch, when whole plants or excised mature leaves were supplied with sucrose. A supply of glucose or fructose, but not of mannitol or sorbitol, to plants also induced the expression of the gene for beta-amylase, and the induction occurred not only in rosette leaves but also in roots, stems, and bracts. These results suggest that the gene for beta-amylase of Arabidopsis is subject to regulation by a carbohydrate metabolic signal, and expression of the gene in various tissues may be regulated by the carbon partitioning and sink-source interactions in the whole plant. The sugar-inducible expression of the gene in Arabidopsis was severely repressed in the absence of light. The sugar-inducible expression in the light was not inhibited by 3(3,4-dichlorophenyl)-1,1-dimethylurea or by chloramphenicol, but it was inhibited by cycloheximide. These results suggest that a light-induced signal and de novo synthesis of proteins in the cytoplasm are involved in the regulation. A fusion gene composed of the 5' upstream region of the gene for beta-amylase from Arabidopsis and the coding sequence of beta-glucuronidase showed the sugar-inducible expression in a light-dependent manner in rosette leaves of transgenic Arabidopsis.     

ROS perception in Arabidopsis thaliana: the ozone-induced calcium response

Ozone is responsible for more crop losses than any other air pollutant. The changes in gene expression, which occur in plants in response to ozone, have been well characterized, yet little is known about how ozone is perceived or the signal transduction steps that follow. The earliest characterized response to ozone is an elevation in cytosolic-free calcium, which takes place within seconds of exposure. In this study, the calcium response to ozone was investigated in Arabidopsis thaliana seedlings using a variety of fumigation protocols. Ozone elicited distinct calcium responses in the aerial tissue and roots of seedlings. The calcium response in the cotyledons and leaves was biphasic and sensitive to the rate at which the ozone concentration increased. The response in the root was monophasic and insensitive to the rate of increase in ozone concentration. Experiments utilizing inhibitors of antioxidant metabolism demonstrated that the magnitude of the first peak in calcium in the aerial tissues was dependent upon the redox status of the plant. Seedlings were shown to be able to distinguish between ozone and hydrogen peroxide, producing a calcium signal in response to one of these reactive oxygen species (ROS) when they had become refractory to the other. Pre-treatment with ozone altered the calcium response to hydrogen peroxide and vice versa, indicating that the calcium response to a given ROS may reflect the stress history of the plant. These data suggest ROS signalling is more sophisticated than previously realized and raise questions over current models of ozone perception.