Lycopersicon Chilense Research Articles

Accumulation of acidic SK3 dehydrins in phloem cells of cold- and drought-stressed plants of the Solanaceae

The role of acidic SK(n) dehydrins in stress tolerance of important crop and model species of the Solanaceae remains unknown. We have previously shown that the acidic SK₃ dehydrin DHN24 from Solanum sogarandinum is constitutively expressed and its expression is associated with cold acclimation. Here we found that DHN24 is specifically localized to phloem cells of vegetative organs of non-acclimated plants. More precise localization of DHN24 revealed that it is primarily found in sieve elements (SEs) and companion cells (CCs) of roots and stems. In cold-acclimated plants, DHN24 is mainly present in all cell types of the phloem. Dhn24 transcripts are also predominantly localized to phloem cells of cold-acclimated stems. Immunoelectron microscopy localized DHN24 to the cytosol and close to organelle membranes of phloem cells, the lumen with phloem protein filaments, parietal cytoplasm of SEs and the nucleoplasm of some nuclei. Cell fractionation experiments revealed that DHN24 was detected in the cytosolic, nuclear and microsomal fractions. We also determined whether homologous members of the acidic subclass dehydrins from Capsicum annuum and Lycopersicon chilense share the characteristics of DHN24. We showed that they are also constitutively expressed, but their protein level is upregulated preferentially by drought stress. Immunofluorescent localization revealed that they are detected in SEs and CCs of unstressed plants and throughout the phloem in drought-stressed plants. These results suggest that one of the primary roles of DHN24 and its homologs may be the protection of the phloem region from adverse effects of abiotic stresses.

The degradation of potato virus M (PVM) particles in plant cells

Degradation of potato virus M particles was observed in the cells of <i>Solanum tuberosum</i>, <i>Solanum rostratum</i>, <i>Lycopersicon esculentum</i> and <i>Lycopersicon chilense</i> plants infected with this virus. PVM particles found in the cytoplasm of infected parenchyma cells grouped together in the form of inclusions, often found near the tonoplast. The ends of the virus particles and the tonoplast came into close contact. Cytoplasmic protrusions containing PVM particles, reaching into vacuoles were formed in those places. In addition to a large central vacuole, small vacuoles were observed in cells containing PVM particles. Various stages of degradation of cytoplasmic protrusions were observed both in the large and small vacuoles.

Course of meiosis in F1 interspecific hybrids of Lycopersicon esculentum Mill. × Licopersicon chilense Dun.

A study was conducted into the course of meiosis in F1 interspecific hybrids of Lycopersicum esculentum Mill (mutant line Mo 638) × Lycopersicum chinense Dul. and its parental forms. An F1 interspecific hybrid was obtained through the embryo culture technique. A decrease in the chiasma frequency and an increase in the frequency of univalents and meiotic abnormalities compared to their parental forms were detected in hybrid plants. The number of univalents and the percentage of main impairments decreased, as the height of bud tier locations increased. A conclusion was made regarding the connection between the regularity of meiosis in the examined F1 interspecific hybrids of Lycopersicon esculentum × Lycopersicon chilense, on the one hand, and the hybrid nature of genotypes and the influence of environmental factors, on the other hand.

Reaction of tomato hybrids carrying the Ty-1 locus to Brazilian bipartite Begomovirus species

The number of tomato-infecting begomoviruses has increased in Brazil after the introduction of the polyphagous vector Bemisia tabaci biotype B. The Ty-1 locus, introgressed from Lycopersicon chilense, controls tolerance to species of the monopartite Tomato yellow leaf curl virus (TYLCV) complex in Europe and the Middle East. However, little information is available about the Ty-1 effectiveness against species of the bipartite Begomovirus complex occurring in Brazil. Heterozygous (Ty-1/ty-1) and homozygous (ty-1/ty-1) hybrids were evaluated for reaction to Begomovirus isolates under open field conditions in two growing areas in Central Brazil. Test plants were evaluated under natural inoculation with high vector pressure. Evaluation was done using a disease assessment scale (DAS) varying from 1= no symptoms to 4= severe symptoms. Systemic infection was evaluated via polymerase chain reaction (PCR) using 'universal' Begomovirus primers. In the trial #1, the hybrids (Ty-1/ty-1) and (ty-1/ty-1) had 35% and 95% of plants with symptoms and 75% and 100% of plants with positive PCR, respectively. In the trial #2, only 20% of the Ty-1/ty-1 hybrid plants were symptom-free with both hybrids displaying 100% of plants with positive PCR. This reaction of the Ty-1 hybrid to bipartite Begomovirus species was similar to that reported in Europe and the Middle East to the TYLCV complex with a large number of plants being neither virus-free nor symptom-free. On the other hand, symptom expression of the Ty-1 hybrid was significantly milder than ty-1/ty-1 hybrids in both trials (DAS = 1.35 vs. 2.70 for the trial #1 and DAS = 2.05 vs. 3.95 for the trial #2). Nucleotide sequencing indicated the presence of isolates genetically related to Tomato rugose mosaic virus (ToRMV) in the trial #1 and a mixed infection of ToRMV and Tomato yellow vein streak virus in the trial #2. Therefore, the Ty-1 locus seems to control a "tolerance" response to distinct Begomovirus species. Resistance gene clusters is a common feature in the tomato genome, particularly at the chromosome 6 where Ty-1 is located. Therefore, additional studies are necessary to confirm if this tolerance to a range of begomoviruses is controlled by Ty-1 alone or a by the action of distinct, closely linked genes.

Involvement of Ethylene in Stress-Induced Expression of the TLC1.1 Retrotransposon from Lycopersicon chilense Dun.

The TLC1 family is one of the four families of long terminal repeat (LTR) retrotransposons identified in the genome of Lycopersicon chilense. Here, we show that this family of retroelements is transcriptionally active and its expression is induced in response to diverse stress conditions such as wounding, protoplast preparation, and high salt concentrations. Several stress-associated signaling molecules, including ethylene, methyl jasmonate, salicylic acid, and 2,4-dichlorophenoxyacetic acid, are capable of inducing TLC1 family expression in vivo. A representative of this family, named TLC1.1, was isolated from a genomic library from L. chilense. Transient expression assays in leaf protoplasts and stably transformed tobacco (Nicotiana tabacum) plants demonstrate that the U3 domain of the 5'-LTR region of this element can drive stress-induced transcriptional activation of the beta-glucuronidase reporter gene. Two 57-bp tandem repeated sequences are found in this region, including an 8-bp motif, ATTTCAAA, previously identified as an ethylene-responsive element box in the promoter region of ethylene-induced genes. Expression analysis of wild-type LTR and single and double ethylene-responsive element box mutants fused to the beta-glucuronidase gene shows that these elements are required for ethylene-responsive gene expression in protoplasts and transgenic plants. We suggest that ethylene-dependent signaling is the main signaling pathway involved in the regulation of the expression of the TLC1.1 element from L. chilense.

(260) Development of SCAR and CAPS Markers Linked to Tomato Begomovirus Resistance Genes Introgressed from Lycopersicon chilense

Resistance to begomoviruses tomato mottle virus (ToMoV) and tomato yellow leaf curl virus (TYLCV) has been introgressed to tomato (Lycopersicon esculentum) from L. chilense accessions LA 1932, LA 2779, and LA 1938. Resistance genes have been mapped to three regions on chromosome 6 using randomly amplified polymorphic DNA (RAPD) markers. We call these regions 1, 2, and 3. To facilitate breeding by marker assisted selection, advanced breeding lines with resistance from the above sources were assayed for the presence of RAPD markers to determine which were most tightly linked to begomovirus resistance. The best RAPD markers were then converted to sequence characterized amplified region (SCAR) markers or cleaved amplified polymorphic sequence (CAPS) markers. In addition, selected restriction fragment length polymorphism (RFLP) markers near the three regions were converted into CAPS markers, which were tested for association with the advanced breeding lines. Only LA 2779 derivatives have the L. chilense introgression in region 1, which is near the location of the Ty-1 gene and spans across CAPS markers 32.5Cla and TG118. Two region 1 RAPD markers UBC197 and UBC621 were converted co-dominant SCAR or CAPS markers, which were present in all 16 resistant breeding lines tested. Derivatives from all three accessions have introgressions in region 2. Further assays with more markers in this region are under way to determine the lengths and locations of the introgressions. No tightly linked RAPD markers have been found for the resistance gene from LA 1932 in region 3. RFLP and CAPS markers are being used to more precisely locate the region 3 gene.

Evaluation of breeding tomato lines partially resistant to Tomato yellow leaf curl Sardinia virus and Tomato yellow leaf curl virus derived from Lycopersicon chilense

Twelve tomato (Lycopersicon esculentum Mill.) advanced breeding lines derived from L. chilense and partially resistant to Tomato yellow leaf curl Sardinia virus (TYLCSV) were evaluated for their resistance to the species from Israel (Tomato yellow leaf curl virus, TYLCV). Two assays were carried out in two consecutive years, using agroinoculation and whitefly-mediated inoculation, respectively. Symptom severity, percentage of infection, and viral DNA accumulation (using molecular hybridization) were measured. In the first assay, the 12 breeding lines were agroinoculated with both virus species. Resistance to TYLCSV was confirmed for the 12 breeding lines, but only 6 of them showed resistance to TYLCV. During the second assay these six breeding lines were whitefly-inoculated with TYLCV. All lines showed high levels of partial resistance to TYLCV consisting in attenuation and delay in time of symptom development and reduction in virus accumulation when compared with the susceptible control. Three of these lines even accumulated significantly lower amounts of viral DNA than the resistant controls 'Anastasia' and 'Boludo' hybrids. These lines also display good horticultural traits, appropriate for the protected growing system and for the fresh market requirements. These advanced breeding lines are base material for developing commercial hybrids highly resistant to TYLCSV and TYLCV.

Breeding for resistance to begomovirus in tropic‐adapted tomato genotypes

AbstractFour tomato lines introgressed from Lycopersicon chilense were compared with the commercial F1 hybrids ‘ARO 8479’ and ‘HA 3108’, which are tolerant to Tomato yellow leaf curl virus, and the cv. ‘Campbell 28’ as a susceptible control. Resistance was evaluated by the use of grafted diseased scions as well as in a field trial where plants infected by viruliferous whiteflies and disease‐free plants were transplanted in paired rows. The new lines LD 3, LD 4, LD 5 and LD 6 showed no disease symptoms after grafting or in the field trial. Virus accumulation at 60 days after transplanting was low in the infected plants: 0.09, 0.60, 1.00 and 0.50 ng, respectively. No fruit‐set or yield losses were registered under the high temperature conditions prevalent in the trial, in which lines LD 5 and LD 6 were better adapted to tropical conditions. Viral DNA concentrations were over 1000 ng in the cvs.‘Campbell 28′,‘ARO 8479’ and ‘HA 3108’. The last two are considered tolerant as they were asymptomatic or had mild symptoms, respectively, but achieved acceptable yields in the trial. By contrast, virus had a negative effect on fruit‐set, number of fruit per plant and total yield in the cv.‘Campbell 28’.

Enhanced Resistance to Verticillium dahliae in Transgenic Strawberry Plants Expressing a Lycopersicon chilense Chitinase Gene

A chitinase gene (pcht28), isolated from Lycopersicon chilense, was transferred into `Joliette' strawberry using a stipule regeneration method and Agrobacterium-mediated gene transfer technique. Stipules showed a high rate of shoot regeneration (>90%) through direct or indirect organogenesis. Stipules were cocultured with a transformation plasmid in which pcht28 was under the control of the CAMV 35S promoter. A high tendency in production of chimaeric shoots was observed. Shoots which did not show any sign of bleaching after several subcultures in kanamycin containing medium were considered as stable transformants. These shoots were successfully rooted in the presence of 50 μg·mL-1 kanamycin. Transgenic nature of the plants was confirmed by PCR as well as Southern blot analysis. Constitutive expression of the chitinase gene was demonstrated by Northern analysis. In growth chamber studies, the transgenic strawberry plants which expressed pcht28 had significantly higher resistance to Verticillium dahliae as compared to nontransgenic controls. These results demonstrate that pcht28 plays a role in defense against this fungal disease in strawberry.

Phenotypic response of Lycopersicon chilense to water deficit

La variacion fenotipica que induce el ambiente en las plantas ha sido considerada como una respuesta que maximiza la adaptacion a ambientes heterogeneos. Lycopersicon chilense, una especie de tomate endemica del Desierto de Atacama, presenta variaciones fenotipicas altitudinales en sus ambientes naturales, las que podrian deberse a diferentes grados de disponibilidad de agua en el suelo. Se hipotetiza que (a) semillas de poblaciones provenientes de distintos ambientes, crecidas en un ambiente comun, presentaran fenotipos semejantes, si las poblaciones no estan diferenciadas geneticamente y que (b) las diferentes poblaciones al ser sometidas a dos niveles de sequia deberian variar su constitucion fenotipica con respecto al grupo control. Se estudio la respuesta de 20 rasgos fenotipicos en nueve poblaciones de Lycopersicon chilense sometidas a distintos niveles de riego. Las semillas fueron colectadas en un gradiente altitudinal (desde los 20 a los 3.075 m de altitud), germinadas, puestas a crecer a las mismas condiciones climaticas y sometidas a tres niveles de riego: bajo (80 % CC), moderado (40 % CC) y severo (20 % CC). A pesar de las diferencias climaticas en sus ambientes naturales, la respuesta fenotipica de las plantas fue semejante en las nueve poblaciones cuando crecieron en un ambiente comun. Diferencias significativas entre las poblaciones se encontraron en tres de los 20 rasgos investigados (el numero de semillas por fruto, el peso fresco de los frutos y el volumen de los frutos). El deficit hidrico indujo una respuesta fenotipica en 12 caracteres. Los mas significantivos fueron: peso seco de las raices, cobertura, numero de frutos cuajados y el numero de semillas por fruto. Interaccion entre las poblaciones y el tratamiento de deficit hidrico se encontro solo en el numero de semillas por fruto, el peso fresco de los frutos y el volumen de los frutos. Nuestros datos indican que la respuesta fenotipica parece no diferir entre las poblaciones cuando estas crecen bajo condiciones ambientales similares. Probablemente la respuesta fenotipica de Lycopersicon chilense en sus ambientes naturales esta mas relacionada con ajustes fisiologicos y metabolicos que con una diferenciacion genetica.

Widening the genetic basis of virus resistance in tomato

New and old accessions of Lycopersicon chilense (LA 1932, LA 1938 and LA 1963), L. peruvianum (PI-143679 and PI-126944), and L. hirsutum (UPV-16910) recently reported as resistant to TSWV, TYLCV and PepMV, viral agents responsible for the most severe economic losses in tomato crop in Spain, were selected as male parents for crosses with L. esculentum in order to widen the genetic basis of virus resistance in tomato. After the analysis of the nature and severity of the barriers found in each case, crossability barriers between wild and cultivated species were circumvented by using several techniques. Crosses with pollen mixture (1:1, wild:cultivated) were successful in obtaining interspecific hybrids with the two L. chilense accessions (LA 1932 and LA 1963) that exhibited more relaxed post-cigotic barriers. Embryo rescue was also successful in crosses with these accessions and also in crosses with L. peruvianum accessions in which embryos beyond the globular stage were found (PI-143679). However, a combination of two or more strategies was necessary in crosses with those accessions exhibiting more severe crossability barriers. Mixture pollen crosses (10:1, wild:cultivated), combined with embryo rescue, allowed for the recovery of hybrids with LA 1938. Stigma and pistil complementation with H 3BO 3 and GA 3, followed by immature seed culture was found to be an effective method for the production of novel interspecific hybrids with PI-126944, the accession with the highest level of resistance to TSWV and TYLCV. By using the best combination of techniques we also backcrossed these interspecific hybrids to tomato to generate the BC1 progeny. The new genes introgressed will be useful to obtain new tomato varieties resistant to TSWV, TYLCV and PepMV.

Inheritance and Linkage of Tomato Mottle Virus Resistance Genes Derived from Lycopersicon chilense Accession LA 1932

Tomato mottle virus (ToMoV) is a silverleaf whitefly (Bemisia argentifolii Bellows and Perring n. sp.) transmitted, bipartite geminivirus that infects tomatoes (Lycopersicon esculentum Mill.). Inbred lines resistant to ToMoV were derived from Lycopersicon chilense Dunal accession LA 1932. Inheritance was studied using a family developed from the crossing of a resistant inbred with a susceptible tomato inbred over two seasons. The F1 had resistance intermediate to the parents and generation means analysis of F1 and F2, backcross and parental populations suggested that the action of at least two additive genes with high heritability (h2n.s. = 0.87) controlled ToMoV resistance. When data from the two seasons were combined, an acceptable fit to an additive-dominance genetic model was obtained. Single plant comparisons, bulk comparisons, and tailends of F2 populations segregating for ToMoV resistance derived from LA 1932 identified randomly amplified polymorphic DNA (RAPD) markers using eight hundred 10-mer oligonucleotide primers. The F2 populations used for inheritance studies were screened for polymorphic markers, and 12 RAPD markers associated with the ToMoV resistant line were linked to the morphological markers self-pruning (sp) and potato leaf (c) on chromosome 6. RAPD markers that were associated with ToMoV resistance segregated into two linked regions flanking either side of the sp and c loci. The molecular studies suggested that the action of at least two additive regions controlled ToMoV resistance which supported the inheritance analysis.

Sources of resistance in Lycopersicon spp. to a bipartite whitefly-transmitted geminivirus from Brazil

Accessions of Lycopersicon chilense, L. peruvianum, L.hirsutum and sixteen L. esculentum genotypes were evaluated undergreenhouse conditions for resistance to a whitefly-transmitted geminivirusisolate from Brasilia-DF (DF1). Artificial cage inoculation oftomato plants at the two true-leaf stage, using 20 viruliferous whiteflies perplant in individual insect-proof cages, ensured 100% infection ofsusceptible tomato plants. Virus infection was confirmed by symptomdevelopment and dot-blot or squash-blot hybridization. In advanced testing,accessions of L. chilense (LA 1967), L. peruvianum (CNPH784) and L. hirsutum (PI-127827) and three selected inbred lines(TY 197, TY 198 and Tx 468-1) showed no symptoms and viral DNAwas barely detectable four weeks after inoculation, indicating good sourcesof resistance to the virus.

Tomato Spotted Wilt Virus (TSWV) resistance in tomato derived from Lycopersicon chilense Dun. LA 1938

Tomato spotted wilt virus (TSWV) resistance wasidentified in Y118 (Fla 925-2), an F1BC1S6 tomato line(Lycopersicon esculentum Mill.), derived from a crosswith L. chilense Dun. (LA 1938). This line waspreviously selected for tomato mottle virus (ToMoV)resistance in Florida. Progeny from crosses betweenFla 925-2 and three different TSWV susceptible L.esculentum parents were used in TSWV resistancestudies. A total of 75 F1 and 596 F2 plants from allthree crosses were screened for TSWV resistance. ForF2 plants free of TSWV symptoms, evaluations were madeusing enzyme-linked immunosorbent assay (ELISA). TenF3 populations used for further greenhouse and fieldscreenings were selected from F2 plants found to befree of the virus using visual and ELISA criteria ateach evaluation. One F1 and four F3 lines werestudied under field conditions (Stellenbosch, SouthAfrica) in which 100% of the `Flora-Dade' susceptiblecontrols were severely infected with TSWV. Theresults of the field study clearly establish that TSWVfield resistance is present in the Fla 925-2 (Y118)derived lines. Studies conducted on these linesrevealed that this resistance has the distinctcharacteristic of often `recovering' from initiallyhigh levels of virus titer in the tissue to levelsbelow detection with ELISA.

Inheritance and genetic mapping of cucumber mosaic virus resistance introgressed from Lycopersicon chilense into tomato

Cucumber mosaic virus (CMV) infects a wide variety of crop plants and in tomato (Lycopersicon esculentum Mill.) causes significant economic losses in many growing regions, particularly the Mediterranean. The objective of the present study was to identify the number and map locations of genes controlling resistance to CMV in breeding lines (BC1–inbreds) derived from the related wild species L. chilense. These lines also carried the gene Tm-2 a for resistance to ToMV, which facilitated the interpretation of disease symptoms. The segregation for CMV resistance in the BC2F1 and BC2F2 generations, following mechanical inoculation with subgroup-I isolates, was consistent with expectations for a single dominant gene, for which the symbol Cmr (cucumber mosaic resistance) was given. Resistant and susceptible BC1-inbreds were analyzed with RFLP and isozyme markers to identify genomic regions introgressed from L. chilense. The only L. chilense-specific markers found were on chromosome 12; some resistant lines contained a single introgression comprising the entire short arm and part of the long arm of this chromosome, while others contained a recombinant derivative of this introgression. The chromosome 12 markers were significantly associated with CMV resistance in both qualitative and quantitative models of inheritance. The qualitative analysis, however, demonstrated that CMV resistance was not expressed as a reliable monogenic character, suggesting a lack of penetrance, significant environmental effects, or the existence of additional (undetected) resistance factors. In the quantitative analysis, the marker interval TG68 – CT79 showed the most significant association with CMV resistance. No association between CMV resistance and the Tm-2 a gene was observed. These breeding lines are potentially useful sources of CMV resistance for tomato improvement, in which context knowledge of the map location of Cmr should accelerate introgression by marker-assisted selection.

Molecular Markers Mapped around the High Shoot Regeneration Capacity Gene Rg-2 in Lycopersicon chilense.

From one BC1F1-44-15 plant(Takashina et al. 1998), which has a high capacity to regenerate shoots from root explants of L.chilense PI128644 and is self-compatible, we obtained the BC1F2 plants. They were analyzed for their capacity to regenerate adventitious shoots from root explants in vitro. The BC1F2 plants showed a bimodal distribution with two groups based on their shoot regeneration rates. Plants with a high shoot regeneration capacity and low shoot regeneration capacity segregated at a 3/1 ratio. This suggests that the shoot regeneration capacity derived from L.chilense PI128644 is controlled by a major dominant gene, which was designated as Rg-2. About 60 random amplified polymorphic DNA (RAPD) bands specific to the wild species used as a parent were generated in the BC1F1-44-15 plant using 140 ranom primers. Ten of the 60 RAPD markers, were linked to the gene for high shoot regeneration capacity by a modified bulked segregant analysis using BC2F1 plants. The segregation of 12 markers(an RFLP marker TG102 mapped on chromosome 3, a marker of the acid invertase gene invchi and 10 RAPD markers) was examined by using a BC1F2 generation. A linkage map of the molecular markers was constructed around the gene Rg-2 for the high shoot regeneration capacity. The gene Rg-2 was located at 3.2 cM from a cluster including seven RAPD markers, as well as the gene invchi.

Transgenic tomato plants expressing a Lycopersicon chilense chitinase gene demonstrate improved resistance to Verticillium dahliae race 2.

An acidic endochitinase gene (pcht28) isolated from Lycopersicon chilense was introduced into tomato (L. esculentum) through Agrobacterium-mediated transformation, using the CAMV 35S promoter. Transgenic plants demonstrated a high level of constitutive expression of pcht28 and chitinase enzyme activity. Kanamycin-resistant R1 plants (resulting from self-pollination of transgenic plants) as well as R2 plants were evaluated for their tolerance to Verticillium dahliae (race 1 and 2 for R1 plants and race 2 for R2 plants) in the greenhouse. They demonstrated a significantly (P<0.05) higher level of tolerance to the fungi compared to the nontransgenic plants, as measured by foliar disease symptoms, vascular discoloration, and vascular discoloration index. The transgenic plants produced in this study represent a source of genetic resistance to Verticillium dahliae.

Developing tomato breeding lines resistant to tomato yellow leaf curl virus

AbstractUsing controlled whitefly‐mediated inoculation techniques, seven Lycopersicon chilense accessions, highly resistant to isolates of tomato yellow leaf curl virus(TYLCV) from Southern Europe, TYLCV‐Sr, were selected. All exhibited similar levels of partial resistance, being symptomless and with low levels of viral DNA accumulation. However, a differential response to infection was found in interspecific hybrids with tomato and inbred lines derived from different L. chilense accessions, allowing a precise discrimination among them. This selection procedure which considers the expression of the resistance genes in the tomato genetic background led to the selection of two highly resistant F1 hybrids derived from L. chilense LA 1932 and LA 1938. A backcrossing programme was initiated, selecting for horticultural characteristics and TYLCV resistance, in field and controlled inoculation conditions. As a result of this programme, six advanced breeding lines (UPV Ty 1, 3, 6, 9, 17 and 53), exhibiting a high level of resistance to TYLCV‐Sr, were obtained. Under high inoculum pressure conditions these lines suffered only 30‐40% yield loss relative to non‐infected control plants, and compared with 90‐95% yield loss in susceptible controls. These lines also have horticultural characteristics appropriate for the fresh market tomato cultivation system in this area, and are a good base material for obtaining commercial hybrids highly resistant to different isolates of TYLCV.

A proline-, threonine-, and glycine-rich protein down-regulated by drought is localized in the cell wall of xylem elements.

A cDNA clone encoding a proline-, threonine-, and glycine-rich protein (PTGRP) was isolated from a wild tomato species (Lycopersicon chilense) (L.X. Yu, H. Chamberland, J.G. Lafontain, Z. Tabaeizadeh [1996] Genome 39: 1185-1193). Northern-blot analysis and in situ hybridization studies revealed that PTGRP is down-regulated by drought stress. The level of the mRNA in leaves and stems of 8-d drought-stressed plants decreased 5- to 10-fold compared with that in regularly watered plants. The mRNA re-accumulated when drought-stressed plants were rewatered. Antibodies raised against a glutathione S-transferase/PTGRP fusion protein were used to elucidate the subcellular localization of the protein by immunogold labeling. In regularly watered L. chilense plants, PTGRP protein was found to be localized in xylem pit membranes and disintegrated primary walls. Examination of sections from drought-stressed plants revealed a significant decrease in the levels of labeling. In these samples, only a few scattered gold particles were detected in the same areas. In the leaf tissues of plants that had been rewatered for 3 d following an 8-d drought stress, the labeling pattern was similar to that of the regularly watered plants. To our knowledge, PTGRP is the first drought-regulated protein that has been precisely localized in the cell wall.

New sources for high resistance of tomato to the tomato spotted wilt virus from Lycopersicon peruvianum

AbstractMechanical inoculation and transmission by thrips in a growth chamber were used in order to screen Lycopersicon peruvianumand Lycopersicon chilense germplasm for tomato spotted wilt virus (TSWV) resistance. Two highly aggressive Spanish TSWV isolates (HA‐931100 and T‐941117), having different restrictotypes were used. L. peruvianum accessions PI‐126935, PI‐126944, CIAPAN 16, PE‐18 and CIAPAN 17 showed high resistance to both isolates in mechanical and thrips transmission. Their resistance appears useful in breeding programmes.