Organ-specific expression of three leaf/stem specific cDNAs from potato is regulated by light and correlated with chloroplast development

Photosynthesis-associated gene families: differences in response to tissue-specific and environmental factors

The endogenous small subunit of the ribulose-1,5-bisphosphate carboxylase gene rbcS and the light-harvesting chlorophyll a/b-binding protein gene (LHCP) of pea are expressed in a light-inducible manner and are active mainly in green chloroplast-containing tissue. Chimeric genes under control of the 5'-flanking sequences of the rbcS ss3.6 or LHCP AB80 genes from pea were used to study the factors relating to the issue-specific and lightinducible expression of these nuclear-encoded genes in transgenic tobacco plants. The results show that plastid development plays a crucial role in the activation of expression of these chimeric genes. Particular members of each of the above gene families respond differently to tissue-specific and environmental factors. Furthermore, the light-inducible expression directed by the 5'-flanking sequence of ss3.6 rbcSgene is not exclusively mediated by phytochrome, but probably is controlledin large part by another photoreceptor.

Transgenic plants as tools to study the molecular organization of plant genes

Transgenic plants are generated in nature by Agrobacterium tumefaciens, a pathogen that produces disease through the transfer of some of its own DNA into susceptible plants. The genes are carried on a plasmid. Much has been learned about how the plasmid is transferred, how the plasmid-borne genes are organized, regulated, and expressed, and how the bacteria's pathogenic effects are produced. The A. tumefaciens plasmid has been manipulated for use as a general vector for the transfer of specific segments of foreign DNA of interest (from plants and other sources) into plants; the activities of various genes and their regulation by enhancer and silencer sequences have been assessed. Future uses of the vector (or others like it that have different host ranges) by the agriculture industry are expected to aid in moving into vulnerable plants specific genes that will protect them from such killers as nonselective herbicides, insects, and viruses.

Analysis of the Transient Increase in Cytosolic Ca2+ during the Action Potential of Higher Plants with High Temporal Resolution: Requirement of Ca2+ Transients for Induction of Jasmonic Acid Biosynthesis and PINII Gene Expression

Plants respond to various abiotic stimuli by activation and propagation of fast electrical signals, action potentials. To resolve the temporal increase in cytosolic Ca(2)(+) during the action potentials of higher plants, we regenerated transgenic potato plants that expressed the Ca(2)(+) photoprotein apoaequorin. These genetically engineered potato plants were used for simultaneous measurements of transient changes in the membrane potential and the Ca(2)(+) luminescence triggered by heat-induced action potentials. High temporal resolution for recording of the fast transient electrical and light signals was accomplished by a sampling rate of 1 kHz. Upon elicitation by heat the membrane potential depolarization preceded the rise of cytosolic Ca(2)(+) by 50-100 ms. Several Ca(2)(+) channel blockers were tested to inhibit the rise in cytosolic Ca(2)(+). Treatment of plants with Ruthenium Red blocked the elevation in cytosolic Ca(2)(+) that was associated with heat-stimulated action potentials. Furthermore, action potentials have been demonstrated to stimulate jasmonic acid biosynthesis and PINII gene expression. Therefore, we measured jasmonic acid and PINII gene expression levels subsequent to action potential initiation by a short heating pulse. As expected, jasmonic acid biosynthesis and PINII gene expression were induced by action potentials. Pretreatment of potato plants with Ruthenium Red inhibited induction of jasmonic acid biosynthesis and PINII gene expression that was generally triggered by heat-activated action potentials.

The gene family encoding the ribulose-(1,5)-bisphosphate carboxylase/oxygenase (Rubisco) small subunit of potato

We determined the nucleotide sequences of five members of the rbcS gene family encoding the small subunit (SSU) of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) of potato. The genomic organization, structure and expression of the genes is compared to the features of the rbcS genes in tomato. Within the two species, Lycopersicon esculentum and Solanum tuberosum, both members of the Solanaceae, the rbcS genes share more interspecific sequence identity, especially in the 5'- and 3'-untranslated regions and the intron sequences, than within one species. However, the expression data of orthologous rbcS genes containing highly identical regulatory cis-acting elements were found to be different, suggesting that the simple finding of these motifs does not automatically imply similar transcriptional and/or post-transcriptional gene regulation.

Rapid, systemic repression of the synthesis of ribulose 1,5-bisphosphate carboxylase small-subunit mRNA in fungus-infected or elicitor-treated potato leaves

The levels of ribulose 1,5-bisphosphate carboxylase small-subunit (SSU) mRNA and protein decreased considerably in potato (Solanum tuberosum L.) leaves upon infection with the pathogenic fungus,Phytophthora infestans, or upon treatment with an elicitor preparation from the fungal culture fluid. This effect occurred systemically throughout the affected leaf, regardless of whether the interaction withP. infestans was compatible or incompatible. Using the comparatively drastic and synchronous response to fungal elicitor, we demonstrated that the repression of SSU synthesis was caused by rapid gene inactivation. The timing of repression was similar to that observed previously for the transcriptional activation of various pathogen defense reactions. This supports the hypothesis that induction of the extensive, multi-component defense response requires repression of other cellular functions to ensure metabolic balance.

Construction of an intron-containing marker gene: splicing of the intron in transgenic plants and its use in monitoring early events in Agrobacterium-mediated plant transformation

Agrobacterium tumefaciens is a commonly used tool for transforming dicotyledonous plants. The underlying mechanism of transformation however is not very well understood. One problem complicating the analysis of this mechanism is the fact that most indicator genes are already active in Agrobacterium, thereby preventing the precise determination of timing and localisation of T-DNA transfer to plant cells. In order to overcome this obstacle a modified prokaryotic indicator gene was constructed. The expression of this indicator gene and its use in analysing early events in Agrobacterium-mediated plant transformation are described. A portable intron, derived from a plant intron, was introduced into the beta-glucuronidase (GUS) gene. In transgenic plants containing this chimaeric gene the intron is spliced efficiently, giving rise to GUS enzymatic activity. Mapping of the splice junction indicates the exact removal of the intron. No GUS activity is detected in agrobacteria containing this construct due to the lack of a eukaryotic splicing apparatus in prokaryotes. Early phases after transformation of Arabidopsis cotyledon explants were analysed using this GUS-intron chimaeric gene showing that as early as 36 h after Agrobacterium infection significant GUS activity is detected. In vivo GUS staining of transformed cells clearly shows that quickly proliferating calli expressing GUS activity are formed, mainly at the cut surface. Minor transformation events occur however throughout the whole cotyledon. These data indicate that Agrobacterium-mediated T-DNA transfer to plants is much more efficient than has been judged from experiments where selection is applied immediately. The intron-containing GUS gene can be used as an optimised marker gene in transient and stable transformation experiments.

Nucleotide sequence and regulated expression of a wound-inducible potato gene (wun1)

Mechanical wounding of potato leaves, stems, roots and tubers leads to a rapid increase of wun1 mRNA. In potato leaves, the wound-induced accumulation of wun1 mRNA is inhibited by the addition of sucrose or other osmotically active agents. This inhibition is organ specific since sucrose does not prevent wun1 mRNA accumulation in wounded tubers. In contrast, expression of patatin was shown to be repressed in tubers by wounding and this repression was reversed by increasing osmotic pressure. Sequence data obtained from the analysis of a wun1 cDNA and a wun1 genomic clone show no homology to any gene known so far. Histochemical data demonstrate a striking analogy in cell specific expression of chimeric genes expressed under the control of the wun1 promoter and the cell specific production of callose in wounded tobacco leaves.

Targeting and glycosylation of patatin the major potato tuber protein in leaves of transgenic tobacco

Patatin, the most abundant protein in the storage parenchyma cells of potato (Solanum tuberosum L.) tubers, is a vacuolar glycoprotein that consists of a number of closely related polypeptides and is encoded by a large gene family. To analyse the glycosylation pattern and the nature of the glycans on a single patatin polypeptide in a heterologous tissue we introduced a single chimaeric patatin gene into tobacco (Nicotiana tabacum L.) and studied its product in leaves. Patatin isolated from the leaves of transgenic tobacco plants is glycosylated at asparagine (Asn)(60), and Asn(90), but the third glycosylation site (Asn(202)) has no glycan. The two glycans are typical small complex glycans with xylose, fucose, mannose and N-acetylglucosamine in a ratio 1:1:3:2, the same ratio as found on patatin isolated from potato tubers. Expression of patatin in tobacco leaves was accompanied by the correct processing of the signal peptide, and the proper targeting of the glyco-protein to the vacuoles of mesophyll cells.

RFLP analysis and linkage mapping in Solanum tuberosum

A morphologically and agronomically heterogeneous collection of 38 diploid potato lines was analysed for restriction fragment length polymorphisms (RFLPs) with 168 potato probes, including random genomic and cDNA sequences as well as characterized potato genes of known function. The use of four cutter restriction enzymes and a fragment separation range from 250 to 2,000 bases on denaturing polyacrylamide gels allowed the detection of RFLPs of a few nucleotides. With this system, 90% of all probes tested showed useful polymorphism, and 95% of those were polymorphic with two or all three enzymes used. On the average, 80% of the probes were informative in all pairwise comparisons of the 38 lines with a minimum of 49% and a maximum of 95%. The percentage of heterozygosity was determined relative to each other for each line and indicated that direct segregation analysis in F1 populations should be feasible for most combinations. From a backcross involving one pair of the 38 lines, a RFLP linkage map with 141 loci was constructed, covering 690 cMorgan of the Solanum tuberosum genome.

Overproduction of alfalfa glutamine synthetase in transgenic tobacco plants

We have obtained transgenic tobacco plants overexpressing the enzyme glutamine synthetase (GS) by fusing an alfalfa GS gene to the cauliflower mosaic virus 35S promotor and integrating it into Nicotiana tabacum var. W38 plants by Agrobacterium tumefaciens mediated gene transfer. The amount of RNA specific to alfalfa GS was about 10 times higher in transgenic tobacco plants than in alfalfa. The alfalfa GS produced by these transgenic plants was identified by Western blotting and represented 5% of total soluble protein in the transformed plants, amounting to a 5-fold increase in specific GS activity and in a 20-fold increase in resistance to the GS inhibitor L-phosphinothricin in vitro. Tissue from GS overproducing plants showed a sevenfold lower amount of free NH3. The amino acid composition of the plant tissue was not altered significantly by GS overproduction. GS overproducing plants were fertile and grew normally. These data show that a high level of expression of a key metabolic enzyme such as glutamine synthetase does not interfere with growth and fertility of plants.

Structure and biogenesis of Chlamydomonas reinhardtii photosystem I

The photosystem I complex of the green alga Chlamydomonas reinhardtii was isolated and fractionated into its two subcomplex components: the core complex (CC I), which contained the reaction center (P-700) and had four polypeptide subunits, and the light-harvesting complex (LHC I) which contained four polypeptides of about 22, 25, 26 and 27 kDa. The 22-kDa apoprotein was isolated as a chlorophyll a and b binding protein. In the isolated photosystem I holocomplex, about ten copies of the 22-kDa LHC I apoprotein are present for each CC I unit. The 22-kDa polypeptide as well as the other three polypeptides of this complex and the subunit II of CC I are translated on 80S cytoplasmic ribosomes, and therefore are coded in the nucleus. During the greening process of the Chlamydomonas reinhardtii y-1 mutant the 22-kDa LHC I polypeptide, which cross-reacts with polyclonal antibodies raised against the Lemna gibba 20-kDa LHC I apoprotein, accumulates in thylakoids at a late stage of their development, and about 2-3 h after the LHC II and CC I subunit II polypeptides have accumulated. Accumulation of the 22-kDa protein during greening is inhibited by cycloheximide but not by chloramphenicol.

Systemic induction of proteinase-inhibitor-II gene expression in potato plants by wounding

The systemic induction of expression of the gene for proteinase inhibitor II after wounding different parts of potato (Solanum tuberosum L.) plants was analysed at the RNA level. Wounding of either leaves or tubers led to an induction of expression of this gene in non-wounded upper and lower leaves as well as in the upper stem segment, whereas no expression was observed in nonwounded roots or in the lower stem segment. The signal mediating the systemic induction in nonwounded tissue must therefore be able to move both acropetally and basipetally. The systemic wound response is specific for the expression of the proteinase-inhibitor-II gene as no influence was observed for the expression of genes encoding the small subunit of ribulose-1,5-bisphosphate carboxylase and the tuber storage protein patatin which were examined in parallel with the proteinase-inhibitor-II gene.

Molecular cloning and sequencing of sucrose synthase cDNA from potato (Solanum tuberosum L.): preliminary characterization of sucrose synthase mRNA distribution

A cDNA library constructed from poly(A)+ RNA from potato tuber in lambda gt11 was screened for sucrose synthase using a maize sucrose synthase cDNA probe. The longest 2.7-kb insert was sequenced. An ATG located within the sequence CTGCAATGG starts an open reading frame of 805 codons. The nucleotide sequence, when compared to the maize sucrose synthase cDNA sequence, exhibits about 70% identity and the deduced amino acid sequence about 75%. Three amino acid regions are about 90% homologous and two of them could be important for the protein function. Expression studies show that transcription of the potato sucrose synthase gene is at least ten fold higher in tubers compared to photosynthetically active tissues.

Expression of nuclear genes as affected by treatments acting on the plastids

In a preceding paper (Oelmüller and Mohr 1986, Planta 167, 106-113) it was shown that in the cotyledons of the mustard (Sinapis alba L.) seedling the integrity of the plastid is a necessary prerequisite for phytochrome-controlled appearance of translatable mRNA for the nuclear-encoded small subunit (SSU) of ribulose-1,5-bisphosphate carboxylase and the light-harvesting chlorophyll a/b-binding protein of photosystem II (LHCP). It was concluded that a signal from the plastid is essential for the expression of nuclear genes involved in plastidogenesis. The present study was undertaken to characterize this postulated signal. Chloramphenicol, an inhibitor of intraplastidic protein synthesis and Norflurazon, an inhibitor of carotenoid synthesis (to bring about photooxidative sensitivity of the plastids) were applied. We obtained the following major results. (i) After a brief period of photooxidative damage a rapid decrease of the above translatable mRNAs was observed.

CONCLUSION

the signal is short-lived and thus required continually. (ii) Once the plastids became damaged by photooxidation, no recovery with regard to nuclear gene expression was observed after a transfer to non-damaging light conditions.

CONCLUSION

even a brief period of damage suffices to prevent production of the signal. (iii) Chloramphenicol inhibited nuclear gene expression (SSU, LHCP) and plastidic development when applied during the early stages of plastidogenesis. Once a certain stage had been reached (between 36-48 h after sowing at 25° C) nuclear gene expression became remarkably insensitive toward inhibition of intraplastidic translation.

CONCLUSION

a certain developmental stage of the plastid must be reached before the signal is released by the plastid. (iv) Under the growth conditions we adopted in our experiments the plastids in the mesophyll cells of mustard cotyledons developed essentially between 36 and 120 (-144) h after sowing. Only during this period could translatable mRNAs for SSU and LHCP be detected.

CONCLUSION

the signal is released by the plastids only during this time span.

The implication of a plastid-derived factor in the transcriptional control of nuclear genes encoding the light-harvesting chlorophyll a/b protein

In carotenoid-deficient albina mutants of barley and in barley plants treated with the herbicide Norflurazon the light-dependent accumulation of the mRNA for the light-harvesting chlorophyll a/b protein (LHCP) is blocked. Thus, the elimination of a functional chloroplast, either as a result of mutation or as a result of herbicide treatment, can lead to the specific suppression of the expression of a nuclear gene encoding a plastid-localized protein. These results confirm and extend earlier observations on maize [Mayfield and Taylor (1984) Eur. J. Biochem. 144, 79-84]. The inhibition of mRNA accumulation appears to be specific for the LHCP; the mRNAs encoding the small subunit of ribulose-1,5-bisphosphate carboxylase and the NADPH: protochlorophyllide oxidoreductase are relatively unaffected. The failure of the albina mutants and of Norflurazon-treated plants to accumulate the LHCP mRNA is not exclusively caused by an instability of the transcript but rather by the inability of the plants to enhance the rate of transcription of the LHCP genes during illumination. Several chlorophyll-deficient xantha mutants of barley, which are blocked after protoporphyrin IX or Mg-protoporphyrin, and the chlorophyll-b-less mutant chlorina f2 accumulate the LHCP mRNA to almost normal levels during illumination. Thus, if any of the reactions leading to chlorophyll formation is involved in the control of LHCP mRNA accumulation it should be one between the formation of protochlorophyllide and the esterification of chlorophyllide a. While the nature of the regulatory factor(s) has not been identified our results suggest that, in addition to phytochrome (Pfr), plastid-dependent factors are required for a continuous light-dependent transcription of nuclear genes encoding the LHCP.