Elevated carbon dioxide plus chronic warming causes dramatic increases in leaf angle in tomato, which correlates with reduced plant growth.

Limited evidence indicates that moderate leaf hyponasty can be induced by high temperatures or unnaturally high CO2 . Here, we report that the combination of warming plus elevated CO2 (eCO2 ) induces severe leaf hyponasty in tomato (Solanum lycopersicum L.). To characterize this phenomenon, tomato plants were grown at two levels of CO2 (400 vs. 700 ppm) and two temperature regimes (30 vs. 37°C) for 16-18 days. Leaf hyponasty increased dramatically with warming plus eCO2 but increased only slightly with either factor alone and was slowly reversible upon transfer to control treatments. Increases in leaf angle were not correlated with leaf temperature, leaf water stress, or heat-related damage to photosynthesis. However, steeper leaf angles were correlated with decreases in leaf area and biomass, which could be explained by decreased light interception and thus in situ photosynthesis, as leaves became more vertical. Petiole hyponasty and leaf-blade cupping were also observed with warming + eCO2 in marigold and soybean, respectively, which are compound-leaved species like tomato, but no such hyponasty was observed in sunflower and okra, which have simple leaves. If severe leaf hyponasty is common under eCO2 and warming, then this may have serious consequences for food production in the future.

Supplemental LED inter-lighting compensates for a shortage of light for plant growth and yield under the lack of sunshine.

Supplemental lighting can enhance yield when sunlight is limited, as in winter. As the effect of frequent cloudy or rainy days in other seasons on plant growth and yield remains unclear, we investigated the effect on tomato (Solanum lycopersicum) and compensation by supplemental LED inter-lighting. Plants were grown under 30% shade cloth on 0%, 40%, or 60% of days. Lower leaves were illuminated with red and blue LED inter-lighting modules from right after first anthesis, or not illuminated. Shading during 40% and 60% of days diminished daily light integral (DLI) by 26% and 40%, respectively, and reduced shoot dry weight by 22.0% and 23.3%, yield by 18.5% and 23.3%, and fruit soluble solids content by 12.3% and 9.3%. In contrast, supplemental inter-lighting improved the light distribution within plants and compensated DLI, and maintained similar yield and soluble solids content in both shade treatments as in the control. These results clearly show that supplemental LED inter-lighting could efficiently compensate for a shortage of light for plant growth, photosynthesis and thus yield under the lack of sunshine.

Remodeling of pectin and hemicelluloses in tomato pericarp during fruit growth.

Tomato fruit texture depends on histology and cell wall architecture, both under genetic and developmental controls. If ripening related cell wall modifications have been well documented with regard to softening, little is known about cell wall construction during early fruit development. Identification of key events and their kinetics with regard to tissue architecture and cell wall development can provide new insights on early phases of texture elaboration. In this study, changes in pectin and hemicellulose chemical characteristics and location were investigated in the pericarp tissue of tomato (Solanum lycopersicon var Levovil) at four stages of development (7, 14 and 21day after anthesis (DPA) and mature green stages). Analysis of cell wall composition and polysaccharide structure revealed that both are continuously modified during fruit development. At early stages, the relative high rhamnose content in cell walls indicates a high synthesis of rhamnogalacturonan I next to homogalacturonan. Fine tuning of rhamnogalacturonan I side chains appears to occur from the cell expansion phase until prior to the mature green stage. Cell wall polysaccharide remodelling also concerns xyloglucans and (galacto)glucomannans, the major hemicelluloses in tomato cell walls. In situ localization of cell wall polysaccharides in pericarp tissue revealed non-ramified RG-I rich pectin and XyG at cellular junctions and in the middle lamella of young fruit. Blocks of non-methyl esterified homogalacturonan are detected as soon as 14 DPA in the mesocarp and remained restricted to cell corner and middle lamella whatever the stages. These results point to new questions about the role of pectin RGI and XyG in cell adhesion and its maintenance during cell expansion.

Growing larger with domestication: a matter of physiology, morphology or allocation?

Domestication might affect plant size. We investigated whether herbaceous crops are larger than their wild progenitors, and the traits that influence size variation. We grew six crop plants and their wild progenitors under common garden conditions. We measured the aboveground biomass gain by individual plants during the vegetative stage. We then tested whether photosynthesis rate, biomass allocation to leaves, leaf size and specific leaf area (SLA) accounted for variations in whole-plant photosynthesis, and ultimately in aboveground biomass. Despite variations among crops, domestication generally increased the aboveground biomass (average effect +1.38, Cohen's d effect size). Domesticated plants invested less in leaves and more in stems than their wild progenitors. Photosynthesis rates remained similar after domestication. Variations in whole-plant C gains could not be explained by changes in leaf photosynthesis. Leaves were larger after domestication, which provided the main contribution to increases in leaf area per plant and plant-level C gain, and ultimately to larger aboveground biomass. In general, cultivated plants have become larger since domestication. In our six crops, this occurred despite lower investment in leaves, comparable leaf-level photosynthesis and similar biomass costs of leaf area (i.e. SLA) than their wild progenitors. Increased leaf size was the main driver of increases in aboveground size. Thus, we suggest that large seeds, which are also typical of crops, might produce individuals with larger organs (i.e. leaves) via cascading effects throughout ontogeny. Larger leaves would then scale into larger whole plants, which might partly explain the increases in size that accompanied domestication.

Distribution of some pectic and arabinogalactan protein epitopes during Solanum lycopersicum (L.) adventitious root development.

BACKGROUND: The adventitious roots (AR) of plants share the same function as primary and lateral roots (LR), although their development is mainly an adaptive reaction to stress conditions. Regeneration of grafted plants is often accompanied by AR formation thus making the grafting technique a good model for studying AR initiation and development and their means of emergence. Pectins and arabinogalactan proteins (AGP) are helpful markers of particular cellular events, such as programmed cell death (PCD), elongation, proliferation or other differentiation events that accompany AR development. However, little is known about the distribution of pectins and AGPs during AR ontogeny, either in the primordium or stem tissues from which AR arise or their correspondence with these events during LR formation. RESULTS: AR were developed from different stem tissues such as parenchyma, xylem rays and the cambium, depending on the stem age and treatment (grafting versus cutting) of the parental tissue. Immunochemical analysis of the presence of pectic (LM8, LM19, LM20) and AGP (JIM8, JIM13, JIM16) epitopes in AR and AR-associated tissues showed differential, tissue-specific distributions of these epitopes. Two pectic epitopes (LM19, LM20) were developmentally regulated and the occurrence of the LM8 xylogalacturonan epitope in the root cap of the AR differed from other species described so far. AGP epitopes were abundantly present in the cytoplasmic compartments (mainly the tonoplast) and were correlated with the degree of cell vacuolisation. JIM8 and JIM13 epitopes were detected in the more advanced stages of primordium development, whereas the JIM16 epitope was present from the earliest division events of the initial AR cells. The comparison between AR and LR showed quantitative (AGP,) and qualitative (pectins) differences. CONCLUSION: The chemical compositions of adventitious and lateral root cells show differences that correlate with the different origins of these cells. In AR, developmental changes in the distribution of pectins and AGP suggest the turnover of wall compounds. Our data extend the knowledge about the distribution of pectin and AGP during non-embryogenic root development in a species that is important from an agronomic point of view.

The Glycerol-3-Phosphate Acyltransferase GPAT6 from Tomato Plays a Central Role in Fruit Cutin Biosynthesis.

The thick cuticle covering and embedding the epidermal cells of tomato (Solanum lycopersicum) fruit acts not only as a protective barrier against pathogens and water loss but also influences quality traits such as brightness and postharvest shelf-life. In a recent study, we screened a mutant collection of the miniature tomato cultivar Micro-Tom and isolated several glossy fruit mutants in which the abundance of cutin, the polyester component of the cuticle, was strongly reduced. We employed a newly developed mapping-by-sequencing strategy to identify the causal mutation underlying the cutin deficiency in a mutant thereafter named gpat6-a (for glycerol-3-phosphate acyltransferase6). To this end, a backcross population (BC1F2) segregating for the glossy trait was phenotyped. Individuals displaying either a wild-type or a glossy fruit trait were then pooled into bulked populations and submitted to whole-genome sequencing prior to mutation frequency analysis. This revealed that the causal point mutation in the gpat6-a mutant introduces a charged amino acid adjacent to the active site of a GPAT6 enzyme. We further showed that this mutation completely abolished the GPAT activity of the recombinant protein. The gpat6-a mutant showed perturbed pollen formation but, unlike a gpat6 mutant of Arabidopsis (Arabidopsis thaliana), was not male sterile. The most striking phenotype was observed in the mutant fruit, where cuticle thickness, composition, and properties were altered. RNA sequencing analysis highlighted the main processes and pathways that were affected by the mutation at the transcriptional level, which included those associated with lipid, secondary metabolite, and cell wall biosynthesis.

Solanum pennellii backcross inbred lines (BILs) link small genomic bins with tomato traits.

We present a resource for fine mapping of traits derived from the wild tomato species Solanum pennellii (LA0716). The population of backcross inbred lines (BILs) is composed of 446 lines derived after a few generations of backcrosses of the wild species with cultivated tomato (cultivar M82; LA3475), followed by more than seven generations of self-pollination. The BILs were genotyped using the 10K SOL-CAP single nucleotide polymorphism (SNP) -Chip, and 3700 polymorphic markers were used to map recombination break points relative to the physical map of Solanum lycopersicum. The BILs carry, on average, 2.7 introgressions per line, with a mean introgression length of 11.7 Mbp. Whereas the classic 76 introgression lines (ILs) partitioned the genome into 106 mapping bins, the BILs generated 633 bins, thereby enhancing the mapping resolution of traits derived from the wild species. We demonstrate the power of the BILs for rapid fine mapping of simple and complex traits derived from the wild tomato species.

Pore size regulates operating stomatal conductance, while stomatal densities drive the partitioning of conductance between leaf sides.

BACKGROUND AND AIMS: Leaf gas exchange is influenced by stomatal size, density, distribution between the leaf adaxial and abaxial sides, as well as by pore dimensions. This study aims to quantify which of these traits mainly underlie genetic differences in operating stomatal conductance (gs) and addresses possible links between anatomical traits and regulation of pore width. METHODS: Stomatal responsiveness to desiccation, gs-related anatomical traits of each leaf side and estimated gs (based on these traits) were determined for 54 introgression lines (ILs) generated by introgressing segments of Solanum pennelli into the S. lycopersicum 'M82'. A quantitative trait locus (QTL) analysis for stomatal traits was also performed. KEY RESULTS: A wide genetic variation in stomatal responsiveness to desiccation was observed, a large part of which was explained by stomatal length. Operating gs ranged over a factor of five between ILs. The pore area per stomatal area varied 8-fold among ILs (2-16 %), and was the main determinant of differences in operating gs between ILs. Operating gs was primarily positioned on the abaxial surface (60-83 %), due to higher abaxial stomatal density and, secondarily, to larger abaxial pore area. An analysis revealed 64 QTLs for stomatal traits in the ILs, most of which were in the direction of S. pennellii. CONCLUSIONS: The data indicate that operating and maximum gs of non-stressed leaves maintained under stable conditions deviate considerably (by 45-91 %), because stomatal size inadequately reflects operating pore area (R(2) = 0·46). Furthermore, it was found that variation between ILs in both stomatal sensitivity to desiccation and operating gs is associated with features of individual stoma. In contrast, genotypic variation in gs partitioning depends on the distribution of stomata between the leaf adaxial and abaxial epidermis.

A quantitative genetic basis for leaf morphology in a set of precisely defined tomato introgression lines.

Introgression lines (ILs), in which genetic material from wild tomato species is introgressed into a domesticated background, have been used extensively in tomato (Solanum lycopersicum) improvement. Here, we genotype an IL population derived from the wild desert tomato Solanum pennellii at ultrahigh density, providing the exact gene content harbored by each line. To take advantage of this information, we determine IL phenotypes for a suite of vegetative traits, ranging from leaf complexity, shape, and size to cellular traits, such as stomatal density and epidermal cell phenotypes. Elliptical Fourier descriptors on leaflet outlines provide a global analysis of highly heritable, intricate aspects of leaf morphology. We also demonstrate constraints between leaflet size and leaf complexity, pavement cell size, and stomatal density and show independent segregation of traits previously assumed to be genetically coregulated. Meta-analysis of previously measured traits in the ILs shows an unexpected relationship between leaf morphology and fruit sugar levels, which RNA-Seq data suggest may be attributable to genetically coregulated changes in fruit morphology or the impact of leaf shape on photosynthesis. Together, our results both improve upon the utility of an important genetic resource and attest to a complex, genetic basis for differences in leaf morphology between natural populations.

The SlFRK4 promoter is active only during late stages of pollen and anther development.

Carbohydrates are essential for male gametophyte development. However, our understanding of the mechanism by which the sugar supply is controlled in the stamen is still in its infancy. We previously reported on the stamen-specific expression of the tomato (Solanum lycopersicum) sugar metabolic gene, fructokinase 4 (SlFRK4). Here, we present the cloning and the characterization of the SlFRK4 promoter and show its differential activation during anther development. We also show that the tissue-specific expression of SlFRK4 promoter is maintained in Arabidopsis thaliana. By histochemical analyses of the GUS reporter gene and DTA toxin driven by the SlFRK4 promoter, we show that the SlFRK4 promoter is gradually activated in pollen grains throughout the later stages of anther development and upon pollen germination. In addition, we analyzed the expression profile of SlFRK4 and other sugar metabolic genes and found that SlFRK4 and the invertase LIN7 are co-expressed in mature and germinated pollen. These findings point to the existence of a specialized mechanism in which carbohydrates are provided to the male gametophyte during the later stages of its development and suggest a valuable tool for manipulating the development of male gametophytes in crop species.

Failure of the tomato trans-acting short interfering RNA program to regulate AUXIN RESPONSE FACTOR3 and ARF4 underlies the wiry leaf syndrome.

Interfering with small RNA production is a common strategy of plant viruses. A unique class of small RNAs that require microRNA and short interfering (siRNA) biogenesis for their production is termed trans-acting short interfering RNAs (ta-siRNAs). Tomato (Solanum lycopersicum) wiry mutants represent a class of phenotype that mimics viral infection symptoms, including shoestring leaves that lack leaf blade expansion. Here, we show that four WIRY genes are involved in siRNA biogenesis, and in their corresponding mutants, levels of ta-siRNAs that regulate AUXIN RESPONSE FACTOR3 (ARF3) and ARF4 are reduced, while levels of their target ARFs are elevated. Reducing activity of both ARF3 and ARF4 can rescue the wiry leaf lamina, and increased activity of either can phenocopy wiry leaves. Thus, a failure to negatively regulate these ARFs underlies tomato shoestring leaves. Overexpression of these ARFs in Arabidopsis thaliana, tobacco (Nicotiana tabacum), and potato (Solanum tuberosum) failed to produce wiry leaves, suggesting that the dramatic response in tomato is exceptional. As negative regulation of orthologs of these ARFs by ta-siRNA is common to land plants, we propose that ta-siRNA levels serve as universal sensors for interference with small RNA biogenesis, and changes in their levels direct species-specific responses.

Functional identification of a novel F-box/FBA gene in tomato.

In plants and animals, the SCF-type ubiquitin protein ligases play an important role in many different physiological processes by regulating protein stability such as S-RNase-based self-compatibility, flower development, hormone responses and meiosis. This study identified an SlFbf gene in tomato that encodes 381 amino acid residues containing a typical F-box motif and an FBA_1 motif associated proteasome pathway; the transcripts of SlFbf was detected in all the tissues (root, stem, leaf, sepal, petal, stamen, pistil, green fruit, breaker fruit and red fruit), with the highest in stamen specifically during flowering stage; SlFbf responded to gibberellins, abscisic acid and light. Suppressed SlFbf leads to bigger pollen and less seeds showing that SlFbf might have an effect on fertilization through regulating stamen development. These findings provide more information about the functions of Fbf gene family.

Changes in regulation of a transcription factor lead to autogamy in cultivated tomatoes.

We report the cloning of Style2.1, the major quantitative trait locus responsible for a key floral attribute (style length) associated with the evolution of self-pollination in cultivated tomatoes. The gene encodes a putative transcription factor that regulates cell elongation in developing styles. The transition from cross-pollination to self-pollination was accompanied, not by a change in the STYLE2.1 protein, but rather by a mutation in the Style2.1 promoter that results in a down-regulation of Style2.1 expression during flower development.

Spatial distribution of bumblebees foraging on two cultivars of tomato in a commercial greenhouse.

The spatial distribution of foraging bumblebees, Bombus terrestris L. (Hymenoptera: Apidae), was studied in a greenhouse planted with two cultivars of tomato, Lycopersicum esculentum Mill. (Solanaceae), in two patches. In both patches, bumblebee densities per square meter were measured on plots, and the results showed that their densities were nearly similar. The densities of available flowers, their pollen production, and availability also were measured. Our results showed that, although the cultivars greatly differed in flower density, flower morphology, and pollen production, their pollen availability (i.e., pollen actually collected by bumblebees per square meter) was approximately the same. Therefore, the mean quantities of pollen collected per bumblebee were similar in each patch. Knowing that bumblebees do not visit different varieties randomly, our results suggest that the major factor affecting the bumblebee distribution among patches was the density of available resource. Results are discussed both from an applied point of view and in relation to the assumptions of the ideal free distribution theory.

The Pseudomonas syringae pv. tomato DC3000 type III effector HopF2 has a putative myristoylation site required for its avirulence and virulence functions.

The HopPtoF locus in Pseudomonas syringae pv. tomato DC3000 harbors two genes, ShcF and HopF2 (previously named ShcF(Pto) and HopF(Pto)), that encode a type III chaperone and a cognate effector protein, respectively. The HopF2 gene has a rare initiation codon, ATA that was reported to be functional only in mitochondrial genes. Here, we report that the native HopPtoF locus of DC3000 confers an avirulence function in tobacco W38 plants, indicating that the ATA start codon directs the synthesis of a functional effector. However, disruption of HopF2 in DC3000 genome did not alter the bacterial virulence in tomato plants. The HopPtoF locus displayed a measurable virulence activity in two strains of P. syringae pv. tomato when the ATA start codon was changed to ATG, and this change also elevated the avirulence function in W38 plants. HopF2 contains a putative myristoylation site. Mutational analysis indicated that this site is required for plasma membrane localization and virulence and avirulence activities of HopF2.

Higher accumulation of proteinase inhibitors in flowers than leaves and fruits as a possible basis for differential feeding preference of Helicoverpa armigera on tomato (Lycopersicon esculentum Mill, Cv. Dhanashree).

Tomato (Lycopersicon esculentum, Mill; cultivar- Dhanashree) proteinase inhibitors (PIs) were tested for their trypsin inhibitory (TI) and Helicoverpa armigera gut proteinases inhibitory (HGPI) activity in different organs of the tomato plants. Analysis of TI and HGPI distribution in various parts of the plant showed that flowers accumulated about 300 and 1000 times higher levels of TI while 700 and 400 times higher levels of HGPI as compared to those in leaves and fruits, respectively. Field observation that H. armigera larvae infest leaves and fruits but not the flowers could be at least partially attributed to the protective role-played by the higher levels of PIs in the flower tissue. Tomato PIs inhibited about 50-80% HGP activity of H. armigera larvae feeding on various host plants including tomato, of larvae exposed to non-host plant PIs and of various larval instars. Tomato PIs were found to be highly stable to insect proteinases wherein incubation of inhibitor with HGP even for 3h at optimum conditions did not affect inhibitory activity. Bioassay using H. armigera larvae fed on artificial diet containing tomato PIs revealed adverse effect on larval growth, pupae development, adult formation and fecundity.

Impact of two fluorescent pseudomonads and an arbuscular mycorrhizal fungus on tomato plant growth, root architecture and P acquisition.

The ability of fluorescent pseudomonads and arbuscular mycorrhizal fungi (AMF) to promote plant growth is well documented but knowledge of the impact of pseudomonad-mycorrhiza mixed inocula on root architecture is scanty. In the present work, growth and root architecture of tomato plants (Lycopersicon esculentum Mill. cv. Guadalete), inoculated or not with Pseudomonas fluorescens 92rk and P190r and/or the AMF Glomus mosseae BEG12, were evaluated by measuring shoot and root fresh weight and by analysing morphometric parameters of the root system. The influence of the microorganisms on phosphorus (P) acquisition was assayed as total P accumulated in leaves of plants inoculated or not with the three microorganisms. The two bacterial strains and the AMF, alone or in combination, promoted plant growth. P. fluorescens 92rk and G. mosseae BEG12 when co-inoculated had a synergistic effect on root fresh weight. Moreover, co-inoculation of the three microorganisms synergistically increased plant growth compared with singly inoculated plants. Both the fluorescent pseudomonads and the myco-symbiont, depending on the inoculum combination, strongly affected root architecture. P. fluorescens 92rk increased mycorrhizal colonization, suggesting that this strain is a mycorrhization helper bacterium. Finally, the bacterial strains and the AMF, alone or in combination, improved plant mineral nutrition by increasing leaf P content. These results support the potential use of fluorescent pseudomonads and AMF as mixed inoculants for tomato and suggest that improved tomato growth could be related to the increase in P acquisition.

Convergent evolution within the genus Solanum: the specialised anther cone develops through alternative pathways.

Many angiosperm species produce cones of anthers which release pollen through pores in response to vibration by pollinating bees ("buzz-pollination"). Anther cones of varying degrees of strength are a defining morphological trait for the genus Solanum. Anthers arranged in a robust ('pepper pot') cone are restricted to a single clade within the genus, and may therefore be assumed to be monophyletic. We show that in some species within this clade, such as tomato (Solanum lycopersicum), the anther cone is held together by interlocking hairs (trichomes) along the edges of the anthers. In other species within the clade, such as woody nightshade (Solanum dulcamara), the expanded anther surfaces are closely appressed to form the tightly bound cone, strengthened by extracellular secretions. Ectopic expression of the MIXTA gene from Antirrhinum majus in S. dulcamara results in the formation of ectopic trichomes on the anthers which cause the cone to disintegrate. Therefore, these two species produce the same macroscopic structure through two mutually exclusive developmental routes and the robust anther cone is derived differently within the clade. This example demonstrates that convergence between closely related species can be easily mistaken for homology, and may thus be underestimated.

Assessment of cross-reactivity between Japanese cedar (Cryptomeria japonica) pollen and tomato fruit extracts by RAST inhibition and immunoblot inhibition.

BACKGROUND: An association between pollinosis and sensitivity to fruits and vegetables has been reported. Although Japanese cedar (Cryptomeria japonica) pollinosis is one of the most widespread diseases in Japan, there have been no reports demonstrating cross-reactivity between Japanese cedar pollen and other plant food. OBJECTIVE: The aim of this study was to demonstrate cross-reactivity between Japanese cedar pollen and tomato fruit (Lycopersicon esculentum) using RAST inhibition and immunoblot inhibition. METHODS: The RAST and immunoblot inhibition were performed using sera from patients with oral allergy syndrome (OAS) after ingesting fresh tomatoes. We identified some proteins that took part in cross-reactive IgE by the determination of N-terminal amino acid sequences and a homology search through the SWISS-PROT database. RESULTS: In the RAST inhibition, the bindings of IgE from the sera from four out of five (4/5) subjects to Japanese cedar pollen discs were inhibited by more than 50% by preincubation of the serum with tomato fruit extracts. Likewise, the IgE bindings to tomato fruit discs were inhibited more than 50% by Japanese cedar pollen extracts in 3/5 sera. In immunoblot inhibition, IgE binding activities of some protein bands on both membranes were decreased by heterologous inhibitors. However, the combinations of these protein bands involved in cross-reactivity were different between patients. CONCLUSION: We have demonstrated cross-reactivity between Japanese cedar pollen and tomato fruit using RAST inhibition and immunoblot inhibition.

A new subfamily of sucrose transporters, SUT4, with low affinity/high capacity localized in enucleate sieve elements of plants.

A new subfamily of sucrose transporters from Arabidopsis (AtSUT4), tomato (LeSUT4), and potato (StSUT4) was isolated, demonstrating only 47% similarity to the previously characterized SUT1. SUT4 from two plant species conferred sucrose uptake activity when expressed in yeast. The K(m) for sucrose uptake by AtSUT4 of 11.6 +/- 0.6 mM was approximately 10-fold greater than for all other plant sucrose transporters characterized to date. An ortholog from potato had similar kinetic properties. Thus, SUT4 corresponds to the low-affinity/high-capacity saturable component of sucrose uptake found in leaves. In contrast to SUT1, SUT4 is expressed predominantly in minor veins in source leaves, where high-capacity sucrose transport is needed for phloem loading. In potato and tomato, SUT4 was immunolocalized specifically to enucleate sieve elements, indicating that like SUT1, macromolecular trafficking is required to transport the mRNA or the protein from companion cells through plasmodesmata into the sieve elements.