Isolation of the LEMMI9 gene and promoter analysis during a compatible plant-nematode interaction.
(9/1525)
Plant-endoparasitic root-knot nematodes feed on specialized giant cells that they induce in the vascular cylinder of susceptible plants. Although it has been established that a number of plant genes change their expression pattern during giant cell differentiation, virtually no data are available about the mechanisms involved in that change. One possibility is differential promoter recognition by the transcription factor(s) responsible for the expression of specific genes. We have isolated and characterized a genomic clone from tomato containing the promoter region of LEMMI9, one of the few plant genes that have been reported to be highly expressed in galls (predominantly in giant cells). The analysis of transgenic potato plants carrying a LEMMI9 promoter-beta glucuronidase (GUS) fusion has demonstrated that the tomato promoter was activated in Meloidogyne incognita-induced galls in a heterologous system. We have located putative regulatory sequences in the promoter and have found that nuclear proteins from the galls formed specific DNA-protein complexes with the proximal region of the LEMMI9 promoter. The nuclear protein-binding sequence mapped to a region of 111 bp immediately upstream from the TATA box. This region contains a 12-bp repeat possibly involved in the formation of DNA-protein complexes, which might be related to the LEMMI9 transcriptional activation in the giant cells. (+info)
Heterologous expression of Arabidopsis phytochrome B in transgenic potato influences photosynthetic performance and tuber development.
(10/1525)
Transgenic potato (Solanum tuberosum) plants expressing Arabidopsis phytochrome B were characterized morphologically and physiologically under white light in a greenhouse to explore their potential for improved photosynthesis and higher tuber yields. As expected, overexpression of functional phytochrome B caused pleiotropic effects such as semidwarfism, decreased apical dominance, a higher number of smaller but thicker leaves, and increased pigmentation. Because of increased numbers of chloroplasts in elongated palisade cells, photosynthesis per leaf area and in each individual plant increased. In addition, photosynthesis was less sensitive to photoinactivation under prolonged light stress. The beginning of senescence was not delayed, but deceleration of chlorophyll degradation extended the lifetime of photosynthetically active plants. Both the higher photosynthetic performance and the longer lifespan of the transgenic plants allowed greater biomass production, resulting in extended underground organs with increased tuber yields. (+info)
The Rx gene from potato controls separate virus resistance and cell death responses.
(11/1525)
Rx-mediated extreme resistance against potato virus X in potato does not involve a necrotic hypersensitive response at the site of initial infection and thereby differs from the more usual type of disease resistance in plants. However, the Rx protein is structurally similar to products of disease resistance genes conferring the hypersensitive response. We show in both Nicotiana spp and potato that Rx has the potential to initiate a cell death response but that extreme resistance is separate and epistatic to necrosis. These data indicate that cell death and pathogen arrest are separate disease resistance responses in plants. (+info)
Antisense-mediated depletion of potato leaf omega3 fatty acid desaturase lowers linolenic acid content and reduces gene activation in response to wounding.
(12/1525)
Fatty acid omega3 desaturases act on membrane lipids to catalyse the formation of trienoic fatty acids, the most abundant in plant tissues being alpha-linolenic acid. This fatty acid is a precursor of jasmonic acid, a plant growth regulator involved in the control of wound-induced gene activation in plants and in the induction of tuberization in potato. We isolated a potato omega3 desaturase cDNA, possibly encoding a plastidial isoform, and used it to investigate its expression pattern throughout plant development and in response to wounding. Plastidial omega3 desaturase gene transcripts accumulate rapidly upon wounding, preceding the jasmonate-dependent induction of the wound-responsive proteinase inhibitor II gene. We generated transgenic potato plants constitutively expressing an antisense RNA to this plastidial omega3 desaturase. Selected transgenic lines in which the cognate omega3 desaturase mRNA is largely depleted show a marked reduction, of up to 60%, in trienoic acids in leaves and tubers. In these lines, a corresponding reduction in jasmonate content and proteinase inhibitor II expression is observed upon wounding. Our results indicate that a reduction in omega3 desaturase mRNA levels compromises the wound-induced activation of proteinase inhibitor II, suggesting that wound-induced synthesis of linolenic acid is required for jasmonic acid production. The antisense-mediated depletion of fatty acid omega3 desaturases is a viable alternative for reducing trienoic fatty acid content in plant species in which a mutant screening approach is not applicable. (+info)
Self-association and mapping of interaction domains of helper component-proteinase of potato A potyvirus.
(13/1525)
Potyviral helper component-proteinase (HC-Pro) is a multifunctional protein involved in aphid transmission, long-distance movement, polyprotein processing, genome amplification and symptom expression. It has been proposed that the active form of HC-Pro is a dimer and that coat protein (CP)-HC-Pro interaction is required for aphid transmission. To test these proposed interactions between CP and HC-Pro of potato A potyvirus (PVA), the yeast two-hybrid system was used. HC-Pro was shown to interact with itself in vivo in yeast cells, as did CP. Taken together with previous observations, we conclude that the functional HC-Pro is a homodimer. Deletion analysis showed that a 24 aa domain in the N-terminal half and the C-terminal proteinase part of HC-Pro were required for the interaction between HC-Pro molecules. No interactions were found between HC-Pro and CP using the genes of aphid-transmissible as well as aphid non-transmissible strains of PVA. (+info)
Potyvirus helper component-proteinase and coat protein (CP) have coordinated functions in virus-host interactions and the same CP motif affects virus transmission and accumulation.
(14/1525)
Amino acid differences between helper component-proteinase (HC-Pro) and coat protein (CP) that are putatively associated with biological differences between isolates PVA-B11 and PVA-U of potato A potyvirus (PVA) were studied using an infectious cDNA clone of PVA-B11. Replacement of the entire CP gene of PVA-B11 with the CP gene of PVA-U reduced virus accumulation in tobacco 5-fold, to the level of PVA-U. In contrast, four simultaneous amino acid substitutions made in PVA-B11 HC-Pro (according to PVA-U HC-Pro) increased virus accumulation 2- to 4-fold. A single substitution (S7G) at the CP N terminus reduced virus accumulation 10-fold, but restored aphid-transmissibility of PVA-B11. Simultaneous mutation of HC-Pro and replacement of CP in B11 delayed systemic movement in tobacco and limited cell-to-cell movement in potato. These results imply coordinated functions of HC-Pro and CP in accumulation and movement of PVA, because the phenotypic effects caused by simultaneous mutation of the two genes were different from the expected 'sum' of phenotypic changes observed following mutation of only one gene at a time. (+info)
Gene for a protein capable of enhancing lateral root formation.
(15/1525)
Analysis of genes preferentially expressed in hairy roots caused by infection with Agrobacterium rhizogenes has provided insights into the regulation of lateral root formation. A hairy root preferential cDNA, HR7, has been cloned from hairy roots of Hyoscyamus niger. HR7 encodes a novel protein partially homologous to a metallocarboxypeptidase inhibitor and is expressed exclusively in the primordium and base of lateral roots in hairy roots. Overexpression of HR7 in transgenic roots of H. niger dramatically enhances the frequency of lateral root formation. The results of this study indicate that expression of HR7 plays a critical role in initiating lateral root formation. (+info)
Chemical cleavage of the overexpressed mitochondrial F1beta precursor with CNBr: a new strategy to construct an import-competent preprotein.
(16/1525)
We have isolated a soluble import-competent 15 kDa N-terminal fragment of the overexpressed Nicotiana plumbaginifolia F1beta precursor of the ATP synthase (N15pF1beta). The isolation was achieved after chemical cleavage, with CNBr, of the insoluble precursor collected in inclusion bodies, followed by purification of the fragment using ion-exchange chromatography. The purity of the final product was estimated to be more than 99%. N15pF1beta contained a presequence of 54 amino acid residues (except for the N-terminal methionine residue) and 82 N-terminal residues of the mature protein. N15pF1beta was shown to be imported into isolated potato tuber mitochondria and to be processed by the isolated mitochondrial processing peptidase (MPP) integrated into the cytochrome bc1 complex of the respiratory chain. Addition of N15pF1beta at micromolar concentrations resulted in the inhibition of import of F1beta precursor and alternative oxidase precursor, synthesized in vitro, into isolated mitochondria as well as the processing of these precursors catalysed by the isolated MPP-bc1 complex. N15pF1beta conjugated via a biotin link to avidin blocked import sites even after the reisolation of mitochondria and inhibited the import of the mitochondrial precursors, indicating that it can be used as a substrate for the generation of a stable translocation intermediate. Our results present a novel procedure for the production of an N-terminal fragment of the F1beta precursor that contains all information necessary for mitochondrial targeting and processing and that can be used for structural and functional studies of the mitochondrial protein import system. This procedure has a general value because it can be used for the production of chemical quantities of any mitochondrial import substrate and presequence peptide. (+info)