Green fluorescent protein as an all-purpose reporter in Petunia

Two critical attributes of a reporter gene are ease of scoring for activity and capacity for expression in all cell types. We have examined a variant of the gene encoding green fluorescent protein,mgfp5, for its ability to meet these criteria in petunia. Under regulation of the Cauliflower Mosaic Virus (CaMV) 35S promoter, GFP was detectable in all vegetative and most floral cell types. Promoters from petuniaadhl andadh2 allowed for production of GFP in those few cell types lacking GFP production from the CaMV 35S promoter, verifying its capacity for expression in all cell types. With the appropriate promoter, GFP fluorescence was thus readily detectable throughout the plant. A potential complication is the green autofluorescence exhibited by some plant tissues. This auto-fluorescence is for the most part distinguishable from that contributed by GFP, but under-scores the need for appropriate controls in GFP-reporter-based experiments. An erratum to this article is available at .     

Comparison of the activities of CaMV 35S and FMV 34S promoter derivatives in Catharanthus roseus cells transiently and stably transformed by particle bombardment

Activities of several CaMV 35S and FMV 34S promoter derivatives fused to the gusA reporter gene were compared in suspension-cultured Catharanthus roseus cells that were transiently and stably transformed using particle bombardment. Our data demonstrate that the 35S and a deletion derivative of the 34S promoter combined with particle bombardment form useful tools for genetic engineering of C. roseus cells. Our results disagree on several points with activities of 35S and 34S promoter derivatives reported for tobacco, indicating that absolute and relative promoter activities can differ between plant species.     

Functional complementation of the Arabidopsis thaliana psbo1 mutant phenotype with an N-terminally His6-tagged PsbO-1 protein in photosystem II

The Arabidopsis thaliana mutant psbo1 has recently been described and characterized. Loss of expression of the PsbO-1 protein leads to a variety of functional perturbations including elevated levels of the PsbO-2 protein and defects on both the oxidizing- and reducing-sides of Photosystem II. In this communication, two plant lines were produced using the psbo1 mutant as transgenic host, which contained an N-terminally histidine₆-tagged PsbO-1 protein. This protein was expressed and correctly targeted into the thylakoid lumen. Immunological analysis indicated that different levels of expression of the modified PsbO-1 protein were obtained in different transgenic plant lines and that the level of expression in each line was stable over several generations. Examination of the Photosystem II closure kinetics demonstrated that the defective double reduction of Q_B and the delayed exchange of Q_BH₂ with the plastoquinone pool which were observed during the characterization of the psbo1 mutant were effectively restored to wild-type levels by the His₆-tagged PsbO-1 protein. Flash fluorescence induction and decay were also examined. Our results indicated that high expression of the modified PsbO-1 was required to increase the ratio of PS II_α/PS II_β reaction centers to wild-type levels. Fluorescence decay kinetics in the absence of DCMU indicated that the expression of the His₆-tagged PsbO-1 protein restored efficient electron transfer to Q_B, while in the presence of DCMU, charge recombination between Q_A⁻ and the S₂ state of the oxygen-evolving complex occurred at near wild-type rates. Our results indicate that high expression of the His₆-tagged PsbO-1 protein efficiently complements nearly all of the photochemical defects observed in the psbo1 mutant. Additionally, this study establishes a platform on which the in vivo consequences of site-directed mutagenesis of the PsbO-1 protein can be examined.     

Viral factor TAV recruits TOR/S6K1 signalling to activate reinitiation after long ORF translation

The protein kinase TOR (target-of-rapamycin) upregulates translation initiation in eukaryotes, but initiation restart after long ORF translation is restricted by largely unknown pathways. The plant viral reinitiation factor transactivator-viroplasmin (TAV) exceptionally promotes reinitiation through a mechanism involving retention on 80S and reuse of eIF3 and the host factor reinitiation-supporting protein (RISP) to regenerate reinitiation-competent ribosomal complexes. Here, we show that TAV function in reinitiation depends on physical association with TOR, with TAV-TOR binding being critical for both translation reinitiation and viral fitness. Consistently, TOR-deficient plants are resistant to viral infection. TAV triggers TOR hyperactivation and S6K1 phosphorylation in planta. When activated, TOR binds polyribosomes concomitantly with polysomal accumulation of eIF3 and RISP--a novel and specific target of TOR/S6K1--in a TAV-dependent manner, with RISP being phosphorylated. TAV mutants defective in TOR binding fail to recruit TOR, thereby abolishing RISP phosphorylation in polysomes and reinitiation. Thus, activation of reinitiation after long ORF translation is more complex than previously appreciated, with TOR/S6K1 upregulation being the key event in the formation of reinitiation-competent ribosomal complexes.     

A novel Glycine soja tonoplast intrinsic protein gene responds to abiotic stress and depresses salt and dehydration tolerance in transgenic Arabidopsis thaliana

Tonoplast intrinsic protein (TIP) is a subfamily of the aquaporin (AQP), also known as major intrinsic protein (MIP) family, and regulates water movement across vacuolar membranes. Some reports have implied that TIP genes are associated with plant tolerance to some abiotic stresses that cause water loss, such as drought and high salinity. In our previous work, we found that an expressed sequence tag (EST) representing a TIP gene in our Glycine soja EST library was inducible by abiotic stresses. This TIP was subsequently isolated from G. soja with cDNA library screening, EST assembly and PCR, and named as GsTIP2;1. The expression patterns of GsTIP2;1 in G. soja under low temperature, salt and dehydration stress were different in leaves and roots. Though GsTIP2;1 is a stress-induced gene, overexpression of GsTIP2;1 in Arabidopsis thaliana depressed tolerance to salt and dehydration stress, but did not affect seedling growth under cold or favorable conditions. Higher dehydration speed was detected in Arabidopsis plants overexpressing GsTIP2;1, implying GsTIP2;1 might mediate stress sensitivity by enhancing water loss in the plant. Such a result is not identical to previous reports, providing some new information about the relationship between TIP and plant abiotic stress tolerance.     

Novel and useful properties of a chimeric plant promoter combining CaMV 35S and MAS elements

The CaMV 35S and Ti plasmid mannopine synthetase (mas) promoters are commonly used by plant genetic engineers. To combine their useful properties, we constructed hybrid promoters incorporating elements from both. These promoters were spliced to the beta-glucuronidase reporter gene and introduced into tobacco and tomato plants by Agrobacterium cocultivation. T1 and T2 transgenic plant populations transformed with different constructs were assayed for the marker enzyme. Comparisons were made based on the range of expression levels found for each promoter construct. We found that a hybrid promoter incorporating the mas region from +65 to -301 and the 35S enhancer region from -90 to -941 had new and interesting properties. This promoter, called Mac, expressed gus at a level three to five times that expressed by a double 35S promoter in the leaves, and 10 to 15 times in hypocotyls and roots. The Mac promoter, however, showed only marginal wound inducibility. Five- to seven-fold wound induction required the presence of the region from -301 to -613 of mas. Reiteration of the 35S enhancer region, from -90 to -430, behind the 35S TATA box region or the mas +65 to -301 region had a smaller effect on expression, ranging from equal to twice the level of the single enhancer control.     

Rol genes alter hormonal requirements for protoplast growth and modify the expression of an auxin responsive promoter

Summary Growth characteristics of tobacco protoplasts containing rolA linked to its own promoter, or the rolB, or rolC genes of Agrobacterium rhizogenes linked to the Cauliflower Mosaic Virus 35S RNA promoter were compared with those from untransformed plants. RolA protoplasts require auxin and cytokinin for callus formation. Protoplasts overexpressing rolB and C form callus in the absence of exogenously applied auxin and cytokinin, respectively. Long term callus growth requires auxin, but the requirement for cytokinin is not critical. Optimal transient expression of an auxin responsive promoter element occurred at lower external levels of auxin in rolB and rolC protoplasts compared with untransformed protoplasts. Addition of putrescine was required for auxin responsive transient gene expression in rolA protoplasts suggesting that polyamines, or their products affect gene expression in rolA plants.Abbreviations T-DNA transferred DNA - TL-DNA left transferred DNA - NAA naphthalene acetic acid - PEG polyethylene glycol - GUS glucuronidase - CaMV cauliflower mosaic virus