Parthenocarpy In Tomato Research Articles

Histological, transcriptomic, and gene functional analyses reveal the regulatory events underlying gibberellin-induced parthenocarpy in tomato

Gibberellin (GA) is one of the major plant hormones that promote parthenocarpy, a highly valuable agronomic trait. Here, we demonstrated that exogenous GA3 application triggered the formation of parthenocarpic fruits with smaller size but unchanged shape in tomato (Solanum lycopersicum). These fruits exhibited a thicker pericarp, undeveloped ovules, and few jelly tissues, leading to smaller locules with empty cavities. Histological investigation showed that GA treatment produced more cell layers with larger cells in the pericarp, suggesting its promotion in both cell division and expansion. Transcriptomic analyses between GA3- and mock-treated unpollinated ovaries/fruits identified a large number of differentially expressed genes related to hormones, cell division, cell expansion, and transcription factors, implying that they coordinately regulated parthenocarpy conferred by GA. In particular, the downregulation of five reported repressors of tomato parthenocarpy, including two auxin signaling components, AUXIN RESPONSE FACTOR5 (SlARF5) and SlARF7, and three MADS-box genes, TOMATO APETALA3 (TAP3), TOMATO PISTILLATA (TPI), and AGAMOUS-LIKE6 (SlAGL6), after GA treatment might play a key role in this process. Furthermore, we found that the knockdown of a GA signaling factor SlMYB33, which was depressed by GA treatment, induced parthenocarpic fruit set in tomato, an effect that might have been achieved by enhancing GA biosynthesis and decreasing the expression of some repressors of tomato parthenocarpy. Thus, our results provide a basis for understanding the regulatory mechanism of GA in tomato parthenocarpy.

Guarding tomato fruit setting in adverse temperatures through the miRNA166-SlHB15A regulatory module

Guarding tomato fruit setting in adverse temperatures through the miRNA166-SlHB15A regulatory module

How Hormones and MADS-Box Transcription Factors Are Involved in Controlling Fruit Set and Parthenocarpy in Tomato.

Fruit set is the earliest phase of fruit growth and represents the onset of ovary growth after successful fertilization. In parthenocarpy, fruit formation is less affected by environmental factors because it occurs in the absence of pollination and fertilization, making parthenocarpy a highly desired agronomic trait. Elucidating the genetic program controlling parthenocarpy, and more generally fruit set, may have important implications in agriculture, considering the need for crops to be adaptable to climate changes. Several phytohormones play an important role in the transition from flower to fruit. Further complexity emerges from functional analysis of floral homeotic genes. Some homeotic MADS-box genes are implicated in fruit growth and development, displaying an expression pattern commonly observed for ovary growth repressors. Here, we provide an overview of recent discoveries on the molecular regulatory gene network underlying fruit set in tomato, the model organism for fleshy fruit development due to the many genetic and genomic resources available. We describe how the genetic modification of components of this network can cause parthenocarpy, discussing the contribution of hormonal signals and MADS-box transcription factors.

A transcriptomic approach to identify regulatory genes involved in fruit set of wild-type and parthenocarpic tomato genotypes.

The tomato parthenocarpic fruit (pat) mutation associates a strong competence for parthenocarpy with homeotic transformation of anthers and aberrancy of ovules. To dissect this complex floral phenotype, genes involved in the pollination-independent fruit set of the pat mutant were investigated by microarray analysis using wild-type and mutant ovaries. Normalized expression data were subjected to one-way ANOVA and 2499 differentially expressed genes (DEGs) displaying a >1.5 log-fold change in at least one of the pairwise comparisons analyzed were detected. DEGs were categorized into 20 clusters and clusters classified into five groups representing transcripts with similar expression dynamics. The "regulatory function" group (685 DEGs) contained putative negative or positive fruit set regulators, "pollination-dependent" (411 DEGs) included genes activated by pollination, "fruit growth-related" (815 DEGs) genes activated at early fruit growth. The last groups listed genes with different or similar expression pattern at all stages in the two genotypes. qRT-PCR validation of 20 DEGs plus other four selected genes assessed the high reliability of microarray expression data; the average correlation coefficient for the 20 DEGs was 0.90. In all the groups were evidenced relevant transcription factors encoding proteins regulating meristem differentiation and floral organ development, genes involved in metabolism, transport and response of hormones, genes involved in cell division and in primary and secondary metabolism. Among pathways related to secondary metabolites emerged genes related to the synthesis of flavonoids, supporting the recent evidence that these compounds are important at the fruit set phase. Selected genes showing a de-regulated expression pattern in pat were studied in other four parthenocarpic genotypes either genetically anonymous or carrying lesions in known gene sequences. This comparative approach offered novel insights for improving the present molecular understanding of fruit set and parthenocarpy in tomato.

A TILLING allele of the tomato Aux/IAA9 gene offers new insights into fruit set mechanisms and perspectives for breeding seedless tomatoes

Parthenocarpy is a desired trait in fruit crops; it enables fruit set under environmental conditions suboptimal for pollination, and seedless fruits represent a valuable consumer product. We employed TILLING-based screening of a mutant tomato population to find genetic lesions in Aux/IAA9, a negative regulator of the auxin response involved in the control of fruit set. We identified three mutations located in the coding region of this gene, including two singlebase substitutions and one single-base deletion, which leads to a frame shift and premature stop codon. The transcription of IAA9 was strongly reduced in the frame-shift mutant, and partial loss of mutated protein activity was evidenced by an in vitro transactivation assay. Whereas missense mutations were predicted to be tolerated and did not cause mutant phenotypes, the frame-shift mutation-induced phenotypes expected for a loss of IAA9 function, including altered axillary shoot growth, reduced leaf compoundness and a strong tendency to produce parthenocarpic fruits. Mutant flowers showed pleiotropic anther cone defects, a phenotype frequently associated with parthenocarpy in tomato and other species. Mutant fruits were larger than those of the seeded control, with higher brix

Cytokinin-Induced Parthenocarpic Fruit Development in Tomato Is Partly Dependent on Enhanced Gibberellin and Auxin Biosynthesis

Fruit set of plants largely depends on the biosynthesis and crosstalk of phytohormones. To date the role of cytokinins (CKs) in the fruit development is less understood. Here, we showed that parthenocarpic fruit could be induced by 1-(2-chloro-4-pyridyl)-3-phenylurea (CPPU, an active CK) in tomato ( Solanum lycopersicum cv. Micro-Tom). The fresh weight of CPPU-induced parthenocarpic fruits was comparable with that induced by GA3. Importantly, CPPU-induced parthenocarpy was found to be compromised by simultaneous application of paclobutrazol (a GA biosynthesis inhibitor), and this effect could be restored by exogenous GA3. Like pollination, CPPU-induced fruit showed enhanced accumulation of GA1+3 and indole-3-acetic (IAA), which were accompanied by elevated expression of GA biosynthesis genes like SlGPS, SlGA20ox1, SlGA20ox2 and SlGA3ox1, and IAA biosynthesis gene ToFZY. Elevated GAs level in CPPU-induced fruits was also associated with down-regulation of GA inactivation genes, namely SlGA2ox1,2,3,4,5 in comparison with untreated control. These results suggested that CKs may induce parthenocarpy in tomato partially through modulation of GA and IAA metabolisms.

Induced parthenocarpic cherry tomato fruits did not shown significant differences in l-ascorbate content but showed different pattern in GalLDH and GME expression

Parthenocarpy in tomato is often induced by auxins to overcome fertilization problems due to low temperatures. To estimate the effect of this agronomical practice on the physiology and dietary value of cherry tomato fruits we determined l-ascorbic acid, the expression and immunolocalization of galactono 1,4 lactone dehydrogenase and the expression of GDP-mannose 3′,5′-epimerase, key genes in l-ascorbic acid biosynthesis. The levels of l-ascorbic acid did not differ between seeded and parthenocarpic fruits while the relative expression of galactono 1,4 lactone dehydrogenase and GDP-mannose 3′,5′-epimerase gene transcripts showed some significant differences between seeded and parthenocarpic fruits. The galactono 1,4 lactone dehydrogenase immunohistolocalization signal was stronger in the ovules and mature embryos of seed-containing fruits. Our data suggest that although there were differences in the expression of the studied genes and in enzyme localization, these did not cause differences in the l-ascorbic acid content of parthenocarpic fruits produced by auxin application.

Over-expression of a grape stilbene synthase gene in tomato induces parthenocarpy and causes abnormal pollen development

A novel strategy to induce parthenocarpy in tomato fruits by the induction of resveratrol biosynthesis in flower tissues was exploited. Two transgenic tomato lines were considered: a higher resveratrol-producing (35SS) line, constitutively expressing a grape stilbene synthase cDNA, and a lower resveratrol-producing (LoxS) line, expressing stilbene synthase under a fruit-specific promoter. The expression of the stilbene synthase gene affected flavonoid metabolism in a different manner in the transgenic lines, and in one of these, the 35SS line, resulted in complete male sterility. Resveratrol was synthesised either in 35SS or LoxS tomato flowers, at an even higher extent (about 8-10 times) in the former line. We further investigated whether stilbene synthase expression may have resulted in impaired naringenin accumulation during flower development. In the 35SS flowers, naringenin was significantly impaired by about 50%, probably due to metabolic competition. Conversely, the amount of glycosylated flavonols increased in transgenic flowers, thereby excluding the diminished production of flavonols as a reason for parthenocarpy in tomato. We further investigated whether resveratrol synthesis may have resulted changes to pollen structure. Microscopic observations revealed the presence of few and abnormal flake-like pollen grains in 35SS flowers with no germination capability. Finally, the analysis of coumaric and ferulic acids, the precursors of lignin and sporopollenin biosynthesis, revealed significant depletion of these compounds, therefore suggesting an impairment in structural compounds as a reason for pollen ablation. These overall outcomes, to the best of our knowledge, reveal for the first time the major role displayed by resveratrol synthesis on parthenocarpy in tomato fruits.

Expression of Parthenocarpy in Tomato Due to Temperature and Pollination Treatment

Parthenocarpy is a condition where an ovary develops into a fruit without fertilization and seed formation. Parthenocarpy might be useful in breeding tomato (Lycopersicon esculentum Mill.) to be adapted to a wide range of temperatures normally unfavorable for fruit setting. The expression of parthenocarpy in tomato, cv. Oregon Pride, was facultative with seedless, few seeded (1–20 seed(s)/fruit), and normal seeded fruit being produced on the same plant in the same growing season. The greatest degree of parthenocarpy, leading to seedlessness, occurred above a daily mean temperature of 24–25˚C. When there was sufficient viable pollen, and an appropriate daily mean temperature of 18–21˚C, there was some fertility leading to low numbers of seed produced. Very low fruit set following emasculation compared to open pollination indicated the requirement of pollination stimulus for fruit set and further development. Precocious ovary development due to genetic stimuli combined with aberration of female fertility by interfering with ovule development might account for very low seed content in fruit of facultative parthenocarpic lines.

Tomato fruit set driven by pollination or by the parthenocarpic fruit allele are mediated by transcriptionally regulated gibberellin biosynthesis

We investigated the role of gibberellins (GAs) in the phenotype of parthenocarpic fruit (pat), a recessive mutation conferring parthenocarpy in tomato (Solanum lycopersicum L.). Novel phenotypes that parallel those reported in plants repeatedly treated with gibberellic acid or having a GA-constitutive response indicate that the pat mutant probably expresses high levels of GA. The retained sensitivity to the GA-biosynthesis inhibitor paclobutrazol reveals that this condition is dependent on GA biosynthesis. Expression analysis of genes encoding key enzymes involved in GA biosynthesis shows that in normal tomato ovaries, the GA20ox1 transcript is in low copy number before anthesis and only pollination and fertilization increase its transcription levels and, thus, GA biosynthesis. In the unpollinated ovaries of the pat mutant, this mechanism is de-regulated and GA20ox1 is constitutively expressed, indicating that a high GA concentration could play a part in the parthenocarpic phenotype. The levels of endogenous GAs measured in the floral organs of the pat mutant support such a hypothesis. Collectively, the data indicate that transcriptional regulation of GA20ox1 mediates pollination-induced fruit set in tomato and that parthenocarpy in pat results from the mis-regulation of this mechanism. As genes involved in the control of GA synthesis (LeT6, LeT12 and LeCUC2) and response (SPY) are also altered in the pat ovary, it is suggested that the pat mutation affects a regulatory gene located upstream of the control of fruit set exerted by GAs.

Induction of parthenocarpy in tomato via specific expression of the rolB gene in the ovary.

The molecular signals for the development of the ovary into fruit following ovule fertilization are not clear. However, in many species, including tomato ( Lycopersicon esculentum Mill.), auxins and auxin transport inhibitors can substitute for fertilization as activators of fruit set, suggesting that this plant hormone plays a key role in this process. In agreement, transgenes for auxin biosynthesis expressed under ovary- or ovule-specific promoters were shown earlier to enable parthenocarpic (i.e. seedless) fruit development. In the present study, we tested an alternative approach for the induction of parthenocarpy that is based on ovary-specific expression of the Agrobacterium rhizogenes-derived gene rolB. This gene was chosen because rolB transgenic plants manifest several syndromes characteristic of auxin treatment. Tomato plants transformed with a chimeric construct containing the rolB gene fused to the ovary- and young-fruit-specific promoter TPRP-F1 developed parthenocarpic fruits. Fruit size and morphology, including jelly fill in the locules of the seedless fruits, were comparable to those of seeded fruits of the parental line. Although it is not known whether ROLB signals for the same cassette of genes involved in fertilization-dependent fruit development, it clearly activates a battery of genes that enable successful completion of seedless fruit development in tomato.

Molecular expression of genes involved in parthenocarpic fruit set in tomato

To characterize the phenomenon of natural parthenocarpy in tomato (Lycopersicon esculentum Mill.) two different approaches have been followed. At a developmental level, the ovary weights of three non‐parthenocarpic lines and three near‐isogenic parthenocarpic (pat‐2) lines were compared. Four developmental stages were considered: flower bud, preanthesis, anthesis and 4 days after anthesis. The parthenocarpic lines displayed ovary weights higher than their respective non‐parthenocarpic lines from preanthesis to 4 days after anthesis. A molecular approach involved comparison of in vitro translation products from flower RNAs taken from the same developmental stages of non‐parthenocarpic and near‐isogenic parthenocarpic (pat‐2 and pat‐3/pat‐4) lines. Analysis by two‐dimensional polyacrylamide gel electrophoresis showed the differential expression of a 30‐kDa product in parthenocarpic materials from preanthesis to anthesis. These results suggest that the physiological and molecular events responsible for parthenocarpy begin at the preanthesis stage, before the flower is completely mature and receptive to pollination. The differential expression of this in vitro translation product in pat‐2 and pat‐3/pat‐4 genotypes also suggests a common or confluent molecular basis in genetically controlled parthenocarpy.

Genetics of parthenocarpy in tomato under a low temperature regime: I. Line RP 75/59

Genetics of parthenocarpy in line RP 75/59 was tested under natural low temperature conditions, under which only seedless fruits were produced. Results were consistent with the hypothesis that three recessive genes with additive effects are responsible for parthenocarpy. Linkage studies, using 40 morphological marker genes located among all tomato chromosomes except chromosome seven, revealed linkage of one gene to diageotropica (dgt) located on chromosome 1 L site 152, and a second gene to yellow verescent (yv) located on chromosome 6 L site 34. Location of the third gene involved in parthenocarpy could not be determined. To calculate the power of the linkage tests, a simulation was carried out for three genetic models; the results are presented graphically in two figures.

Occurrence of Gibberellin A3 in Parthenocarpic Apple Fruit

The gibberellins have been established as effective fruit setting agents (5). In 'the apple, where auxins are generadlly inactive, the giibberellins induce parthenocarpy and sustain fruit growth to maturity (2,6,10). This pronounced fruit-setting activity and the established observation -that asymmetric growth of apple fruit is related to incomplete seed development, has encouraged investigations on the relationship of endogenous seed gibberellins to fruit-set and growth. Gibiberellin-like activity ihas been demonstrated in endosperm (11) and GA4 and GA7 iden'tilfied in immature apple 'seed (8). The biosynthesis of gibberellins by 'seeds is viewed as a specific role of seeds in fruit-set of the apple (7). However, some cultivars of Malus are prone to produce seedless fruit after exposure to 'low temperature during the fruit-setting period. The presence of giibberellinlile substances in such parthenocarpic fruit is, herein, reported. Immature seedless apple fruits (Malus sylvestris Mill., selectiion New Jersey 12) developing subsequent to a severe 'frost, 4 days after full bloom, were -harvested (6-wk post-'bloom), frozen immedi;ately and stored at -30? until' used. Frozen fruits (6.9 kg) were immersed in 100 % acetone (7.6 -liters), then each fruit was halved to check for seedlessness (no seeds were found), homogenized 'in acetone and extracted twice by stirring under nitr-ogen for 24 hours at 2?. The filtrates were combined and concentrated to an aqueous solution (3.5,1iters, pH of 2.8) in vacuo. The pH of the filtrate was increased to 6.0 with 10 % KOH !(13) and centrifuged to remove proteins and other insoluble substances. The supernate was washed with n-hexane and adjusted to pH 2.0, stirred for 2 hours aifter aiddition of 70 g of activated charcoal and filtered. The charcoal was washed several times with distilled water and eluted with acetone. The eluate (acetone) was evaporated ito dryness, the residue (2.62 g) suispended in phosphate buffer (0.2 M, pH 6.2) and extracted with chloroform (9). The aqueous phase was adjusted ,to pH 2.5 with suilfuric acid and extracted with ethyl acetate. The chlorofom and ethyl aicetate extracts were dried over anhydrous sodium sulfate and evaporated to dryness yielding residues of 0.108 and 0.690 g, respectively. Tihese residues were taken ,up in ethanol and lanolin paste preparations of either fraction were found to induce parthenocarpy in tomato. The chloroform fraction was more active than the ethyl acetate fraction. Considerable quantities of inhibitors we-re present in the ethyl acetate fraction as was evidenced by injury of treated ovaries. Further puriification was aohieved by streaking the extracts on Whatman 3 MM paper (57 X 46 am) and developing with isopropanol :ammonium hydroxide:water (10:1:1 v/v). The chromatograms were cut transversely, at intervailis of 0.1 RF, and eluted with 80 % ethanod. The gi;bberellin aictivity of each eluate was assessed uising dwarf pea (9) (cv. Morse's Progress No. 9) and eticutmber seedling (4) (cv. Burpee Hybrid) assays. The chloroform fraction contained an active component(s) migrating to RF 0.4 to 0.7 and which was similar in activity and RF with authentic GA. treated tinder identical conditions (fig 1). A greater quantitative response was obtained from the chloroform than ethyl acetate fraction (approx 10-folld) in the dwarf pea assay. Little or no activity was observed for both fractions in the cucumber assay. Further purification was limited to the active component(s) of the chloroform fraction migrating to RF 0.4 to 0.7. The eluate was streaked on silica gel-G plates (E. Merck F-254, 250 p). Plates were developed with the lower phase of carbon tetrachloride :acetic acid :water (8:3 :5, v/v) plus 20 % ethyl acetate. The active component(s) did not migrate, thtus it was elluted from the origin with ethanol and rechromatographed tusing benzene: n-'butanol :acetic acid (70:25 :5 v/v) as the developing solvent. The active component(s) was identical to GA1 and/or GA3 with respect to RF (0.54) and color of filtorescence and differed in both respects 1 Michigan Agricultural Experiment Station Journal Article No. 4227.