Tomato Species Research Articles

Heterogeneous expression pattern of tandem duplicated sHsps genes during fruit ripening in two tomato species

The small heat shock proteins (sHSPs) have been found to play a critical role in physiological stress conditions in protecting proteins from irreversible aggregation. To characterize the gene expression profile of four sHsps with a tandem gene structure arrangement in the domesticated Solanum lycopersicum (Heinz 1706) genome and its wild close relative Solanum pimpinellifolium (LA1589), differential gene expression analysis using RNA-Seq was conducted in three ripening stages in both cultivars fruits. Gene promoter analysis was performed to explain the heterogeneous pattern of gene expression found for these tandem duplicated sHsps. In silico analysis results contribute to refocus wet experiment analysis in tomato sHsp family proteins.

Natural Variation in Tomato Reveals Differences in the Recognition of AvrPto and AvrPtoB Effectors from Pseudomonas syringae

The Pto protein kinase from Solanum pimpinellifolium interacts with Pseudomonas syringae effectors AvrPto or AvrPtoB to activate effector-triggered immunity. The previously solved crystal structures of the AvrPto-Pto and AvrPtoB-Pto complexes revealed that Pto binds each effector through both a shared and a unique interface. Here we use natural variation in wild species of tomato to further investigate Pto recognition of these two effectors. One species, Solanum chmielewskii, was found to have many accessions that recognize only AvrPtoB. The Pto ortholog from one of these accessions was responsible for recognition of AvrPtoB and it differed from Solanum pimpinellifolium Pto by only 14 amino acids, including two in the AvrPto-specific interface, glutamate-49/glycine-51. Converting these two residues to those in Pto (histidine-49/valine-51) did not restore recognition of AvrPto. Subsequent experiments revealed that a single substitution of a histidine-to-aspartate at position 193 in Pto, which is not near the AvrPto-specific interface, was sufficient for conferring recognition of AvrPto in plant cells. The reciprocal substitution of aspartate-to-histidine-193 in Pto abolished AvrPto recognition, confirming the importance of this residue. Our results reveal new aspects about effector recognition by Pto and demonstrate the value of using natural variation to understand the interaction between resistance proteins and pathogen effectors.

Improving agronomic water use efficiency in tomato by rootstock-mediated hormonal regulation of leaf biomass

Water availability is the most important factor limiting food production, thus developing new scientific strategies to allow crops to more efficiently use water could be crucial in a world with a growing population. Tomato is a highly water consuming crop and improving its water use efficiency (WUE) implies positive economic and environmental effects. This work aimed to study and exploit root-derived hormonal traits to improve WUE in tomato by grafting on selected rootstocks. Firstly, root-related hormonal parameters associated to WUE were identified in a population of recombinant inbred lines (RILs) derived from the wild tomato species Solanum pimpinellifolium. A principal component analysis (PCA) revealed that some hormonal traits were associated with productivity (plant biomass and photosynthesis) and WUE in the RIL population. Leaf ABA concentration was associated to the first component (PC1) of the PCA, which explained a 60% of the variance in WUE, while the ethylene precursor ACC and the ratio ACC/ABA were also associated to PC1 but in the opposite direction. Secondly, we selected RILs according to their extreme biomass (high, B, low, b) and water use (high, W, low, w), and studied the differential effect of shoot and root on WUE by reciprocal grafting. In absence of any imposed stress, there were no rootstock effects on vegetative shoot growth and water relations. Finally, we exploited the previously identified root-related hormonal traits by grafting a commercial tomato variety onto the selected RILs to improve WUE. Interestingly, rootstocks that induced low biomass and water use, ‘bw’, improved fruit yield and WUE (defined as fruit yield/water use) by up to 40% compared to self-grafted plants. Although other hormonal factors appear implicated in this response, xylem ACC concentration seems an important root-derived trait that inhibits leaf growth but does not limit fruit yield. Thus tomato WUE can be improved exploiting rootstock-derived hormonal signals which control leaf growth.

A TILLING approach to generate broad‐spectrum resistance to potyviruses in tomato is hampered by eIF4E gene redundancy

Genetic resistance to pathogens is important for sustainable maintenance of crop yields. Recent biotechnologies offer alternative approaches to generate resistant plants by compensating for the lack of natural resistance. Tomato (Solanum lycopersicum) and related species offer a model in which natural and TILLING-induced potyvirus resistance alleles may be compared. For resistance based on translation initiation factor eIF4E1, we confirm that the natural allele Sh-eIF4E1(PI24)-pot1, isolated from the wild tomato species Solanum habrochaites, is associated with a wide spectrum of resistance to both potato virus Y and tobacco etch virus isolates. In contrast, a null allele of the same gene, isolated through a TILLING strategy in cultivated tomato S. lycopersicum, is associated with a much narrower resistance spectrum. Introgressing the null allele into S. habrochaites did not extend its resistance spectrum, indicating that the genetic background is not responsible for the broad resistance. Instead, the different types of eIF4E1 mutations affect the levels of eIF4E2 differently, suggesting that eIF4E2 is also involved in potyvirus resistance. Indeed, combining two null mutations affecting eIF4E1 and eIF4E2 re-establishes a wide resistance spectrum in cultivated tomato, but to the detriment of plant development. These results highlight redundancy effects within the eIF4E gene family, where regulation of expression alters susceptibility or resistance to potyviruses. For crop improvement, using loss-of-function alleles to generate resistance may be counter-productive if they narrow the resistance spectrum and limit growth. It may be more effective to use alleles encoding functional variants similar to those found in natural diversity.

Solanum watneyi, a new bush tomato species from the Northern Territory, Australia named for Mark Watney of the book and film "The Martian".

A new species of andromonoecious Solanum from the Australian “bush tomato clade” of Solanum subgenus Leptostemonum is described. Solanum watneyi Martine & Frawley, sp. nov. is closely allied with Solanum eburneum, and is sympatric with it in parts of its range in the Northern Territory. The new species has been recognized as a variant of Solanum eburneum for decades, at times being referred to by local botanists as Solanum sp. “Bullita” because of its relative abundance in the vicinity of the Bullita Station area of Judbarra/Gregory National Park. Morphometric analyses show that Solanum watneyi differs statistically from Solanum eburneum in several key reproductive and vegetative characters and field observations suggest that the two sister species may represent a case of edaphic speciation. We provide morphometric evidence for the novelty of Solanum watneyi, a complete description, and cite specimens for both species.

Dissect style response to pollination using metabolite profiling in self-compatible and self-incompatible tomato species

Tomato style is the pathway for pollen germination and pollen tubes growth from the stigma to the ovules where fertilization occurs. It is essential to supplying the nutrients for pollen tube growth and guidance for the pollen tubes. To our knowledge, style also regulates gametophytic self-incompatibility (SI) in tomato species. This study identified the metabolites and monitored the metabolic changes of self-incompatible and self-compatible tomato with self-pollinated or unpollinated styles by gas chromatography-mass spectrometry (GC-MS). A total of 9 classes of compounds were identified in SI and self-compatibility (SC) self-pollinated and unpollinated styles which included amino acids, sugars, fatty acids/lipids, amines, organic acids, alcohols, nitriles, inorganic acids and other compounds. The contents of d-Mannose-6-phosphate, Cellobiose, Myristic acid, 2,4-Diaminobutyric acid, Inositol and Urea were significantly decreased and the rest did not significantly change in SI styles. But change of metabolites content significantly happened in SC styles. In addition, among the total 9 classes of compounds, the different metabolites accounted for a different proportion in amino acids, sugars, amines, organic acids and alcohols compared SC and SI. The result indicated that the physiological changes of styles existed differences in SC and SI after self pollination.

Novel resistance mechanisms of a wild tomato against the glasshouse whitefly.

The glasshouse whitefly, Trialeurodes vaporariorum, is an important pest of many crop plants including tomato, Solanum lycopersicum. Many wild tomato species exhibit a higher resistance to whiteflies. Therefore, locating the source of this enhanced resistance and breeding it into commercial tomato species is an important strategy to reduce the impact of pests on crops. Here, we assessed the pest resistance of Lycopersicon pimpinellifolium by comparing oviposition and feeding data from T. vaporariorum on this wild tomato species with data collected from a susceptible commercial tomato, S. lycopersicum var. ‘Elegance’. The location of resistance factors was examined by use of electrical penetration graph (EPG) studies on these tomato species. Results show that whiteflies preferentially settled on the commercial tomato more often in 80 % of the replicates when given free choice between the two tomato species and laid significantly fewer eggs on L. pimpinellifolium. Whiteflies exhibited a shorter duration of the second feeding bout, reduced pathway phase probing, longer salivation in the phloem and more non-probing activities in the early stages of the EPG on the wild tomato species compared to the commercial tomato. These findings evidence that a dual mode of resistance is present in this wild tomato against T. vaporariorum: a post-penetration, pre-phloem resistance mechanism and a phloem-located factor, which to the best of our knowledge is the first time that evidence for this has been presented. These findings can be used to inform future breeding strategies to increase the resistance of commercial tomato varieties against this important pest.

Resistance to Crown and Root Rot Caused by Phytophthora capsici in a Tomato Advanced Backcross of Solanum habrochaites and Solanum lycopersicum.

Phytophthora capsici causes devastating disease on many vegetable crops, including tomato and other solanaceous species. Solanum habrochaites accession LA407, a wild relative of cultivated tomato, has shown complete resistance to four P. capsici isolates from Michigan cucurbitaceous and solanaceous crops in a previous study. Greenhouse experiments were conducted to evaluate 62 lines of a tomato inbred backcross population between LA407 and the cultivated tomato 'Hunt 100' and 'Peto 95-43' for resistance to two highly virulent P. capsici isolates. Roots of 6-week-old seedlings were inoculated with each of two P. capsici isolates and maintained in the greenhouse. Plants were evaluated for wilting and plant death three times per week for 5 weeks. Significant differences were observed in disease response among the inbred tomato lines. Most lines evaluated were susceptible to P. capsici isolate 12889 but resistant to isolate OP97; 24 tomato lines were resistant to both isolates. Heritability of Phytophthora root rot resistance was high in this population. Polymorphic molecular markers located in genes related to resistance and defense responses were identified and added to a genetic map previously generated for the population. Resistant lines and polymorphic markers identified in this study are a valuable resource for development of tomato varieties resistant to P. capsici.

Acylsugar Acylhydrolases: Carboxylesterase-Catalyzed Hydrolysis of Acylsugars in Tomato Trichomes.

Glandular trichomes of cultivated tomato (Solanum lycopersicum) and many other species throughout the Solanaceae produce and secrete mixtures of sugar esters (acylsugars) on the plant aerial surfaces. In wild and cultivated tomato, these metabolites consist of a sugar backbone, typically glucose or sucrose, and two to five acyl chains esterified to various positions on the sugar core. The aliphatic acyl chains vary in length and branching and are transferred to the sugar by a series of reactions catalyzed by acylsugar acyltransferases. A phenotypic screen of a set of S. lycopersicum M82 × Solanum pennellii LA0716 introgression lines identified a dominant genetic locus on chromosome 5 from the wild relative that affected total acylsugar levels. Genetic mapping revealed that the reduction in acylsugar levels was consistent with the presence and increased expression of two S. pennellii genes (Sopen05g030120 and Sopen05g030130) encoding putative carboxylesterase enzymes of the α/β-hydrolase superfamily. These two enzymes, named ACYLSUGAR ACYLHYDROLASE1 (ASH1) and ASH2, were shown to remove acyl chains from specific positions of certain types of acylsugars in vitro. A survey of related genes in M82 and LA0716 identified another trichome-expressed ASH gene on chromosome 9 (M82, Solyc09g075710; LA0716, Sopen09g030520) encoding a protein with similar activity. Characterization of the in vitro activities of the SpASH enzymes showed reduced activities with acylsugars produced by LA0716, presumably contributing to the high-level production of acylsugars in the presence of highly expressed SpASH genes.

Potential use of edible crops in the phytoremediation of endosulfan residues in soil

Endosulfan is a persistent and toxic organochlorine pesticide of banned or restricted use in several countries. It has been found in soil, water, and air and is bioaccumulated and magnified in ecosystems. Phytoremediation is a technology that promises effective and inexpensive cleanup of contaminated hazardous sites. The potential use of tomato, sunflower, soybean and alfalfa species to remove endosulfan from soil was investigated. All species were seeded and grown in endosulfan-spiked soils (8000 ng g−1 dry weight) for 15 and 60 days. The phytoremediation potential was evaluated by studying the endosulfan levels and distribution in the soil-plant system, including the evaluation of soil dehydrogenase activity and toxic effects on plants. Plant endosulfan uptake leads to lower insecticide levels in the rhizosphere with regards to bulk soil or near root soil at 15 days of growth. Furthermore, plant growth-induced physical-chemical changes in soil were evidenced by differences in soil dehydrogenase activity and endosulfan metabolism. Sunflower showed differences in the uptake and distribution of endosulfan with regard to the other species, with a distribution pesticide pattern of aerial tissues > roots at 15 days of growth. Moreover, at 60 days, sunflower presented the highest pesticide levels in roots and leaves along with the highest phytoextraction capacity. Lipid peroxidation levels correlated positively with endosulfan accumulation, reflecting the negative effect of this insecticide on plant tissues. Considering biomass production and accumulation potential, in conjunction with the reduction of soil pesticide levels, sunflower plants seem to be the best phytoremediation candidate for endosulfan residues in soils.

Phenology, agronomic and nutritional potential of three wild husk tomato species (Physalis, Solanaceae) from Mexico

Physalis includes species cultivated for their edible fruits. In Mexico, the fruits of several wild species of Physalis are harvested for consumption. However, these species of local use have not been evaluated to determine their value as a horticultural crop. The objective of this study was to assess the response to cultivation in P. acutifolia, P. chenopodifolia and P. pubescens and to document their phenology and the nutritional properties of the fruits. Three populations of each species were selected and one population of P. angulata, cultivated in central Jalisco, was used as control. We employed a complete randomized block experimental design with three replications per population that were evaluated two year. The phenology was recorded and codified using the BBCH system (Biologische Bundesanstalt, Bundessortenamt and Chemical industry). Agronomic potential was assessed with six descriptors and multivariate methods. Nutritional potential was determined through physicochemical analyses and nutritional composition of the fruit. The response to agricultural management of the three wild species was positive (85–90% germination, 100% of plants established). Of the populations studied, 78% have an agronomic potential that is similar to the control species (9.9–18.5tha−1); however, this potential differed statistically between crop cycles and among populations across the crop cycles, due to environmental factors, whereas no effect was found at species level. The phenology of the assessed species consists of eight main Phases (Phases 3 and 4 of the BBCH scale are absent) and high correlations (r=0.78–0.98) were found between short periods in the early Phases and subsequent Phases, allowing prediction of earliness. In addition, the nutritional value of their fruits was similar to other cultivated Solanaceae, with pH values ranging from 4.11 to 4.84 and sweetness of 7.4–10.8 on the Brix grade. The studied species are good candidates for breeding and selection programs and for development as new crops of nutritional quality.

The RING Finger E3 Ligase SpRing is a Positive Regulator of Salt Stress Signaling in Salt-Tolerant Wild Tomato Species.

Protein ubiquitination in plants plays critical roles in many biological processes, including adaptation to abiotic stresses. Previously, RING finger E3 ligase has been characterized during salt stress response in several plant species, but little is known about its function in tomato. Here, we report that SpRing, a stress-inducible gene, is involved in salt stress signaling in wild tomato species Solanum pimpinellifolium 'PI365967'. In vitro ubiquitination assay revealed that SpRing is an E3 ubiquitin ligase and the RING finger conserved region is required for its activity. SpRing is expressed in all tissues of wild tomato and up-regulated by salt, drought and osmotic stresses, but repressed by low temperature. Green fluorescent protein (GFP) fusion analysis showed that SpRing is localized at the endoplasmic reticulum. Silencing of SpRing through a virus-induced gene silencing approach led to increased sensitivity to salt stress in wild tomato. Overexpression of SpRing in Arabidopsis thaliana resulted in enhanced salt tolerance during seed germination and early seedling development. The expression levels of certain key stress-related genes are altered both in SpRing-overexpressing Arabidopsis plants and virus-induced gene silenced tomato seedlings. Taken together, our results indicate that SpRing is involved in salt stress and functions as a positive regulator of salt tolerance.

A comparative in vitro study of salt tolerance in cultivated tomato and related wild species.

Salinity stress is a major abiotic stress for plants worldwide. This study was carried out to determine the variation in salt tolerance for 12 different genotypes belonging to three different tomato species: Solanum lycopersicum (L), S. peruvianum (L) and S. pimpinellifolium (L). Shoot apices and callus cultures were exposed to different levels of salinity stress ranging from no salt (control) to 100, 200 and 300 mmol L-1 NaCl. All growth and physiological parameters were significantly affected by salt stress. Most shoot apices of S. lycopersicum did not develop roots when exposed to low NaCl levels, whereas apices of S. peruvianum and S. pimpinellifolium developed roots when exposed to all salt levels. This difference in salt tolerance was clearly shown on the basis of root fresh weights and root surface areas. Callus growth in response to increased salinity was much greater in S. peruvianum and S. pimpinellifolium than in S. lycopersicum. The Cl- and Na+ concentrations increased significantly with increasing salt in the three species, although the S. peruvianum lines accumulated more ions compared with the others. As the salt concentration increased, less K+ accumulated in S. lycopersicum compared to the related wild species. The results obtained in this study suggest that S. peruvianum line 0043-1 was the accession with the best salt tolerance. The most tolerant cultivated tomato (S. lycopersicum) cultivar was 'Rutgers.' Both S. peruvianum line 0043-1 and S. lycopersicum 'Rutgers' are good candidates for inclusion in tomato breeding programs for salt-tolerance.

Chitosan seed soaking: germination and growth of Coriandrum sativum and Solanum lycopersicum

Chitosan seed soaking: germination and growth of Coriandrum sativum and Solanum lycopersicum

Response of some wild species of tomato againstPeanut bud necrosis virusunder open-field conditions

Thrips-borne Tospovirus pathogens adversely affect many globally important crops. Among 16 distinct virus species in the Tospovirus genus, four species including Peanut bud necrosis virus (PBNV) causing necrosis disease in tomato have been reported in India. Identification of stable sources and further utilization of wild relatives as gene sources to increase levels and diversify the bases of resistance may offer good management for the disease. A total of 13 wild species of tomato (Solanum peruvianum), two S. pimpinellifolium, one S. chilense, one S. pennellii and three check cultivars (S. lycopersicum) along with two cultivars (S. lycopersicum) having the Sw-5 and Sw-7 genes were evaluated under field conditions during three consecutive seasons (June to October 2008, July to December 2009, August 2010 to February 2011). Among all, a high degree of field resistance (>80%) was detected in seven lines of S. peruvianum (L00735, L00671, L00887, L06138), S. chilense (TL02226) and S. pimpinellifolium (L03708, TL02213) lines. The field data was also supported by negative reaction against a polyclonal antiserum of the nucleocapsid protein (N) of PBNV in direct antigen coating-enzyme linked immunosorbent assay (DAC-ELISA). The cultivars with Sw-5 and Sw-7 genes were highly susceptible to PBNV.

Evaluation of liquid formulations of Bt against gram pod borer, Helicoverpa armigera (Hubner) and spotted pod borer, Maruca vitrata (Geyer) in pigeonpea

Virulence of native entomopathogenic nematodes against major lepidopteran insect species of tomato (Solanum lycopersicum L.)Neelam Thakur, Preety Tomar, Simranjeet Kaur, Poonam Kumari

In vitro reconstruction and analysis of evolutionary variation of the tomato acylsucrose metabolic network

Plant glandular secreting trichomes are epidermal protuberances that produce structurally diverse specialized metabolites, including medically important compounds. Trichomes of many plants in the nightshade family (Solanaceae) produce O-acylsugars, and in cultivated and wild tomatoes these are mixtures of aliphatic esters of sucrose and glucose of varying structures and quantities documented to contribute to insect defense. We characterized the first two enzymes of acylsucrose biosynthesis in the cultivated tomato Solanum lycopersicum. These are type I/IV trichome-expressed BAHD acyltransferases encoded by Solyc12g006330--or S. lycopersicum acylsucrose acyltransferase 1 (Sl-ASAT1)--and Solyc04g012020 (Sl-ASAT2). These enzymes were used--in concert with two previously identified BAHD acyltransferases--to reconstruct the entire cultivated tomato acylsucrose biosynthetic pathway in vitro using sucrose and acyl-CoA substrates. Comparative genomics and biochemical analysis of ASAT enzymes were combined with in vitro mutagenesis to identify amino acids that influence CoA ester substrate specificity and contribute to differences in types of acylsucroses that accumulate in cultivated and wild tomato species. This work demonstrates the feasibility of the metabolic engineering of these insecticidal metabolites in plants and microbes.

Protein modeling and molecular dynamics simulation of SlWRKY4 protein cloned from drought tolerant tomato (Solanum habrochaites) line EC520061.

WRKY genes are members of one of the largest families of plant transcription factors and play an important role in response to biotic and abiotic stresses, and overall growth and development. Understanding the interaction of WRKY proteins with other proteins/ligands in plant cells is of utmost importance to develop plants having tolerance to biotic and abiotic stresses. The SlWRKY4 gene was cloned from a drought tolerant wild species of tomato (Solanum habrochaites) and the secondary structure and 3D modeling of this protein were predicted using Schrödinger Suite-Prime. Predicted structures were also subjected to plot against Ramachandran's conformation, and the modeled structure was minimized using Macromodel. Finally, the minimized structure was simulated in the water environment to check the protein stability. The behavior of the modeled structure was well-simulated and analyzed through RMSD and RMSF of the protein. The present work provides the modeled 3D structure of SlWRKY4 that will help in understanding the mechanism of gene regulation by further in silico interaction studies.

Resistance to viral yellow leaf curl in tomato through RNAi targeting two Begomovirus species strains

Tomato yellow leaf curl disease caused by different begomovirus species leads to substantial tomato production losses worldwide. In Taiwan, the monopartite tomato leaf curl Taiwan virus (ToLCTWV) and bi-partite tomato yellow leaf curl Thailand virus (TYLCTHV) are the predominant begomovirus species causing this disease. Resistance genes are available in wild tomato species and a continuous search for new resistance genes and alternative control methods is required to respond to the rapid evolution of virus strains. RNA interference is an efficient technology to induce resistance against viral pathogens. Six different sections of the ToLCTWV genome were tested in transformed tomato for their capacity to reduce symptoms and inhibit viral DNA accumulation. The two most effective constructs for ToLCTWV infection carried regions of the C1 and C2 genes, and portions of either the C3 or C4 gene of ToLCTWV. A RNAi construct containing fusions of C1, C2 and C3 sections of ToLCTWV and the corresponding sections of the TYLCTHV DNA-A genome were introgressed into tomato line CLN1621L. R1 and R2 families were challenged using viruliferous whiteflies in separate screen houses for ToLCTWV and TYLCTHV. Sixteen and 12 R2 plants derived from one primary transformant remained symptomless until at least 3 weeks after exposure to ToLCTWV and TYLCTHV, respectively, and accumulated only very low titres of viral DNA, as shown by real-time polymerase chain reaction analysis. Our results suggest that expression of bi-viral RNAi constructs in tomato can lead to resistance against two different tomato infecting begomovirus species.

Meeting Report: Plant Science Student Conference (PSSC) 2015--Young researchers in green biotechnology.

Meeting Report: Plant Science Student Conference (PSSC) 2015--Young researchers in green biotechnology.