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Diagram of a monoecious zucchini squash plant showing the disposition of male and female flowers on the main stem.
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Results from two trials carried out under different environmental conditions indicated that the high temperatures reached in greenhouses during the Spring-Summer growing season are the main environmental factor inducing production of zucchini fruits with attached flowers. The fact that the incidence of this characteristic is genotype-dependent, wit...
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Parthenocarpy is becoming an essential trait for off-season greenhouse production of Zucchini squash. Given that winter conditions promote a reduction in the number of male flowers and in the activity of pollinators, the application of synthetic auxins is currently the most widespread method to induce fruit set. We have evaluated the parthenocarpic...
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... Several ethylene biosynthesis, perception, signalling, and response genes have been identified and characterized in C. pepo since Huang and others (1991) identified the first ACS gene in this species (CpACS1 and CpACS2). We previously cloned and characterized one ACO gene (CpACO1), three ethylene receptor genes (Peñaranda and others 2007; Payán and others 2008), and two CTR-like genes (CpCTR1 and CpCTR2; Manzano and others 2010b). ...
It is well established that ethylene is the main hormonal regulator of sexual expression in the Cucurbitaceae family, controlling not only the sexual fate of individual floral buds, but also the female flower transition, that is, the time at which the first female flower appears and therefore the number of female flowers per plant. Although sex determination of individual flower buds is known to be controlled by specific ethylene biosynthesis ACS genes in melon and cucumber, the role of ethylene genes in the control of the transition to female flowering is still unknown. We have identified two contrasting monoecious inbred lines of Cucurbita pepo, Bolognese (Bog) and Vegetable spaghetti (Veg), which differ in female flower transition but not in flower development. In Bog, which is very sensitive to ethylene, the transition to female flowering is very early, whereas in Veg, which is much less sensitive to ethylene, the transition occurs much later. In this article we compare the production of ethylene and the expression profiles of seven genes involved in the biosynthesis, perception, and signalling of ethylene in the two contrasting lines. Bog, with earlier female flower transition, showed higher ethylene production and CpACO1 expression in the apex at an earlier stage of plant development, when Bog is already producing female flowers, but Veg has not transitioned to female flowering yet. Moreover, the expression of the ethylene receptor and CTR-like genes in the apex of Veg and Bog plants indicates that these genes negatively regulate female flower transition during the earlier stages of plant development. The earlier transition to female flowering in Bog is not only associated with a higher production of ethylene in the apex but also with a premature decline of ethylene negative regulators (receptors and CTR-like) in the apex of the plant. These results provide the basis for a model that explains the regulation of female flowering transition in monoecious cucurbits
... The hybrid cultivar Cavili is able to develop parthenocarpic fruits of commercial size in absence of pollination or hormonal treatments [25]. The parthenocarpy of this cultivar is associated with an incomplete andromonoecy, i.e. a partial conversion of female into bisexual flowers, and a delay in floral organ maturation (Figure 4). ...
... We have recently observed that a reduction of ethylene in female flowers of zucchini can not only promote the development of stamens in the flower, converting female into bisexual flowers, but also induce the parthenocarpic fruit development in absence of pollination and fertilization [25]. This is also true for some cultivars of zucchini squash grown under high temperature conditions [25]. To study the role of ethylene in fruit set and early fruit development in zucchini squash, the present paper compares the production of ethylene and the expression of ethylene biosynthesis and response genes between pollinated and unpollinated ovaries of a non-parthenocarpic cultivar, as well as between a parthenocarpic and a non-parthenocarpic cultivar of zucchini squash. ...
... The low level of ethylene biosynthesis and signalling in pistils at early stages of zucchini fruit development could be coupled with an induction of auxins, one of the main regulators of fruit set in different plant systems [25,33]. We have shown that the application of auxins and TIBA in the flower at anthesis promoted the growth of unfertilized ovaries in the non-parthenocarpic cv. ...
We have identified a kind of parthenocarpy in zucchini squash which is associated with an incomplete andromonoecy, i.e. a partial conversion of female into bisexual flowers. Given that andromonoecy in this and other cucurbit species is caused by a reduction of ethylene production in the female flower, the associated parthenocarpic development of the fruit suggested the involvement of ethylene in fruit set and early fruit development.
We have compared the production of ethylene as well as the expression of 13 ethylene biosynthesis and signalling genes in pollinated and unpollinated ovaries/fruits of two cultivars, one of which is parthenocarpic (Cavili), while the other is non-parthenocarpic (Tosca). In the latter, unpollinated ovaries show an induction of ethylene biosynthesis and ethylene signal transduction pathway genes three days after anthesis, which is concomitant with the initiation of fruit abortion and senescence. Fruit set and early fruit development in pollinated flowers of both cultivars and unpollinated flowers of Cavili is coupled with low ethylene biosynthesis and signalling, which would also explain the partial andromonoecy in the parthenocarpic genotype. The reduction of ethylene production in the ovary cosegregates with parthenocarpy and partial andromonoecy in the selfing progeny of Cavili. Moreover, the induction of ethylene in anthesis (by ethephon treatments) reduced the percentage of bisexual parthenocarpic flowers in Cavili, while the inhibition of ethylene biosynthesis or response (by AVG and STS treatments) induces not only andromonoecy but also the parthenocarpic development of the fruit in both cultivars.
Results demonstrate that a reduction of ethylene production or signalling in the zucchini flower is able to induce fruit set and early fruit development, and therefore that ethylene is actively involved in fruit set and early fruit development. Auxin and TIBA treatments, inducing fruit set and early fruit development in this species, also inhibit ethylene production and the expression of ethylene biosynthesis and response genes. A model is presented that discusses the crosstalk between ethylene and auxin in the control of fruit set and early fruit development in zucchini squash.
... Sex expression in this family of plants can be modified by environmental factors, including light intensity, photoperiod and temperature. Winter conditions, with short days, low light intensity and low night temperatures promote the production of female flowers, while summer conditions increase the production of male flowers (Wien 1997; Peñaranda et al. 2007). In C. pepo, low temperature inhibits the development of male flowers and increases the number of female flower per plant (Wien et al. 2004), while high temperature induces both a partial transformation of female flowers into hermaphrodites and a complete transformation of female flowers into male ones (Peñaranda et al. 2007). ...
... Winter conditions, with short days, low light intensity and low night temperatures promote the production of female flowers, while summer conditions increase the production of male flowers (Wien 1997; Peñaranda et al. 2007). In C. pepo, low temperature inhibits the development of male flowers and increases the number of female flower per plant (Wien et al. 2004), while high temperature induces both a partial transformation of female flowers into hermaphrodites and a complete transformation of female flowers into male ones (Peñaranda et al. 2007). Phytohormones are the main modulators of sex expression in the Cucurbitaceae family. ...
In this paper we compare the sensitivity of different squash genotypes to ethylene and brassinosteroids by studying the effects
of different ethylene and brassinosteroid treatments on the sexual expression and flower development of different C. pepo genotypes: Bolognese (Bog) and Vegetable Spaghetti (Veg), two contrasting lines for ethylene production and sensitivity, as well as Cora, a standard commercial hybrid. Results have demonstrated that ethylene has a much greater effect on sexual expression and
flower development in C. pepo than brassinosteroids. Ethephon increases the number of female flowers per plant and reduces the first male phase of development,
while treatments with the ethylene inhibitors AVG and STS reduce the number of female flowers per plant and expand the first
male phase of development. The differential response observed between genotypes appears to be related to ethylene production
and sensitivity. Bog, which produces more ethylene and is more sensitive to this hormone, responded much better to AVG and STS, reducing the number
of female flowers per plant, while Veg, which is characterised by lower production of and sensitivity to ethylene, responded better to ethephon by reducing the
first male phase of development and increasing the number of female flowers per plant. The differential abortion of female
and male flowers in ethephon, AVG and STS treatments, as well as the occurrence of bisexual flowers in the AVG and STS treated
plants of the more ethylene sensitive genotypes, demonstrate that ethylene is also involved in the development of female flowers.
Female flower buds require a minimal level of ethylene not only to complete their development and maturation without a premature
abortion, but also to arrest the development of stamens in the third whorl and to promote the appropriate growth of the carpels.
On the contrary, the role of brassinosteroids in the sexual expression of C. pepo was not so evident. The application of brassinazole, an inhibitor of brassinosteroid biosynthesis slightly changes the production
of ethylene in the three analysed genotypes, but those changes have little effect on their sexual phenotypes, and they do
not alter the development of the unisexual flowers.
... By contrast, varieties of Cucurbita pepo are all monoecious and produce male or female flowers in the leaf axils. Sex expression of C. pepo, as in other species of the family, varies throughout plant development and it is possible to distinguish three different developmental phases (Peñaranda and others 2007). During the first phase plants produce only male flowers. ...
... In C. pepo low temperature inhibits the development of male flowers and increases the number of female flowers per plant (Wien and others 2004), whereas high temperature induces the production of male flowers (Peñaranda and others 2007). Phytohormones are the main modulators of sex expression in cucurbit species. ...
... Various studies have previously shown that ethylene is the principal component in the control of sex determination in C. pepo, and that its application has a feminizing effect on various C. pepo varieties, reducing the male phase of development and increasing the number of female flowers per plant (Matlob and Basher 1983; Payán and others 2006; Peñaranda and others 2007). Accordingly, the application of ethylene inhibitors lengthens the initial male phase of development and reduces the number of female flowers per plant (Payán and others 2006; Peñaranda and others 2007). To date, however, no ethylene mutant has been isolated and characterized in this species. ...
External treatment with ethylene had indicated earlier that this hormone is the main factor controlling sex determination
in Cucurbita pepo. Up to now, however, there was no genetic evidence that supported the relationship between ethylene production, or perception,
and sexual expression in this species. Here we demonstrate that the extreme male phenotype of the Vegetable Spaghetti (Veg) inbred line of C. pepo subspecies pepo is determined by a major gene that confers reduced ethylene sensitivity in plants. The production of female flowers in the
Veg line is very delayed and reduced with respect to the contrasting Bolognese (Bog) line, ranging between 5 and 35% of female flowers per plant. This enhanced maleness trait segregates as a single gene in
the F2 and backcross (BC) generations, and co-segregates with a weak ethylene-insensitive phenotype in the F2 population, suggesting that the gene responsible for the Veg phenotype could be the result of a mutation in a receptor or response gene for ethylene. Although the etiolated seedlings
of the Veg line, and the most androecious plants in the F2 generation, produce more ethylene than those of the contrasting line, they are less sensitive to this hormone, as indicated
by a weaker triple response and a delayed abscission of ethylene-treated male flowers. Given that the sexual phenotype of
F2 plants is correlated with ethylene sensitivity, with the more sensitive plants producing the higher number of female flowers,
our results demonstrate that the ethylene response is directly involved in the control of sex determination in C. pepo. It regulates the induction of female flower production, and therefore the extension of the initial phase of development
in which the plant produces only male flowers, as well as the number of female flowers per plant.
Keywords
Cucurbita pepo
-Sex expression-Ethylene production-Ethylene sensitivity
Parthenocarpy is becoming an essential trait for off-season greenhouse production of Zucchini squash. Given that winter conditions promote a reduction in the number of male flowers and in the activity of pollinators, the application of synthetic auxins is currently the most widespread method to induce fruit set. We have evaluated the parthenocarpic tendency of 48 long-fruited accessions of Cucurbita pepo spp. pepo, from morphotypes Zucchini, Vegetable marrow and Cocozelle, including 45 traditional cultivars and 3 commercial hybrids, with the goal of identifying new sources of parthenocarpy for breeding programs. After the first screening, 20 selected accessions were evaluated for the growth rate of unpollinated fruit. Twelve of the selected accessions identified as either strongly parthenocarpic or non-parthenocarpic, were compared for fruit rate growth, ethylene production and ethylene sensitivity. Apart from the three control hybrids, the fastest parthenocarpic fruit growth was observed in 'CpCAL112', 'CM-37', 'E-27', 'PI261610', and 'V-185'. The source of the parthenocarpy of some of these accessions differs from that of the hybrids as it was not associated with the conversion of female into bisexual flowers or with the so-called "fruits with attached flowers" syndrome, which is an undesirable trait in current parthenocarpic hybrids. The alternative sources of parthenocarpy may be of great importance in current Zucchini breeding programs. We also demonstrate that the parthenocarpy of these accessions is associated with downregulation of ethylene production in unpollinated fruits during the first days post anthesis (DPA). In non-parthenocarpic accessions, unpollinated fruits boosted ethylene production at 3 DPA, concomitantly with fruit abortion and senescence, while in parthenocarpic accessions, fruits produced little ethylene at 3 DPA. Therefore, ethylene production in ovaries/fruits at 3 DPA can be used as a marker to identify and select parthenocarpy in Zucchini squash. However, in the cultivars tested here, ethylene production and sensitivity in vegetative organs and in male flowers earlier than 3 PDA do not appear well associated with parthenocarpy. © 2014 Springer Science+Business Media Dordrecht.
A new genetic resource for Cucurbita pepo has been developed with chemically induced mutagenesis. The seeds of the zucchini cultivar MU-CU16 were treated with 40 mM–80 mM ethyl methanesulfonate (EMS), reaching high germination rates between 70 and 85%. However, most plants of those M1 populations did not produce offspring, and the fertility rates were lower in plants treated with higher concentrations of EMS. Once we established that visual flower abnormality rates were not sufficient to explain low fruit yield, pollen viability was analysed with fluorochromatic reaction. Compared with untreated plants, treatment with EMS produced a substantial decrease in pollen viability, and only the group of plants with pollen viability rates higher than 45% yielded nearly 70% of fruits with seeds. Therefore, the main issues to be addressed for developing mutant lines in this species are to increase the number of mutations in the genome and to increase the number of mutant lines with sufficient fertility. In this case, the early plantlet selection for high pollen viability carried out as part of this work represents a useful tool for use in future breeding programs by mutagenesis, allowing an increase of up to 40% in the production of mutant lines for a dosage of 65 mM EMS.
In the zucchini squash, Cucurbita pepo, a well coordinated abscission of the female flower during fruit set is essential to obtain a fruit of commercial value.
In Spain zucchini is mainly produced in greenhouses in Almería, where high temperatures during the spring-summer period provoke
a cultivar-dependent defect in fruits known as the “sticky flower” syndrome. This disorder is characterised by an arrest in
growth and maturation of floral organs, and a lack of female floral abscission, thus diminishing fruit shelf-life, commercial
quality and value. The aim of the present work was to improve knowledge of the abscission process in C. pepo to better understand the fundamental causes of this disorder. The anatomical analysis of abscission shows a well defined
male floral abscission zone (AZ), few hours after anthesis, which differs from the female zone which is not differentiated
from the adjacent tissue until the abscission process has begun, and which occurs as a consequence of AZ cell enlargement
and the dissolution of their cell walls. To evaluate the role of ethylene and auxins in the regulation of floral abscission
in zucchini we performed several treatments, with: ethylene, added as 0.25% ethrel solution; AVG, the inhibitor of ethylene
synthesis, at 100μM; indol-3-acetic acid, 100μM; and TIBA, the inhibitor of auxin polar transport, at 10mM. These treatments
show that ethylene is an accelerator of zucchini floral abscission, and also promotes abscission in isolated AZs of sticky
flowers. On the other hand, IAA delays abscission of the female flowers, whilst the inhibitor of auxin polar transport promotes
it. The activity of the cell wall hydrolytic enzymes, polygalacturonase and cellulase, sharply increased just before the shedding
of zucchini floral organs (72h after anthesis). Moreover, both enzyme activities were induced by ethylene, which partly explains
the ethylene promoting effect.
Ethylene is one of the most important hormones for flowering of cucumber (Cucumis sativus L.). The molecular interaction between cucumber and ethylene was investigated by construction and characterization of a suppression
subtractive hybridization cDNA library from stem apex of ethrel-treated cucumber. To screen differentially expressed genes,
dot blotting was used with cDNA probes prepared from mRNAs isolated from control and ethrel-treated samples. Acquired positive
clones were subjected to sequence and homology search analysis. In total, 103 expressed sequence tags (ESTs) were acquired
after screening; among these, 73 showed significant sequence similarity to known genes, 26 had unknown functions, and four
clones did not match any known sequences. Gene ontology (GO) analysis revealed that ESTs with known functions were involved
in photosynthesis, metabolism, protein synthesis, cellular communication and transport, signal transduction, and transcriptional
regulation. The expression levels and overall profiles in female and male buds of 11 ESTs were confirmed by reverse transcription
polymerase chain reaction (RT–PCR) and three of them were detected by real-time quantitative PCR (qRT–PCR) in the whole plant.
One of these was an F-box protein, EBF1 (EIN3 BINDING F-BOX1), which might play a positive role in female expression of cucumber.
Keywords
Cucumis sativus L.–Suppression subtractive hybridization–Ethrel–Gene expression–Sex expression
Ethylene is an essential regulator of flower development in Cucurbita pepo, controlling the sexual expression, and the differentiation and maturation of floral organs. To study the action mechanism of ethylene during the male and female flower development, we have identified two CTR1 homologues from C. pepo, CpCTR1 and CpCTR2, and analysed their expressions during female and male flower development and in response to external treatments with ethylene. CpCTR1 and CpCTR2 share a high homology with plant CTR1-like kinases, but differ from other related kinases such as the Arabidopsis EDR1 and the tomato LeCTR2. The C-terminal ends of both CpCTR1 and CpCTR2 have all the conserved motifs of Ser/Thr kinase domains, including the ATP-binding signature and the protein kinase active site consensus sequence, which suggests that CpCTR1 and CpCTR2 could have the same function as CTR1 in ethylene signalling. The transcripts of both genes were detected in different organs of the plant, including roots, leaves and shoots, but were mostly accumulated in mature flowers. During the development of male and female flowers, CpCTR1 and CpCTR2 expressions were concomitant with ethylene production, which indicates that both genes could be upregulated by ethylene, at least in flowers. Moreover, external treatments with ethylene, although did not alter the expression of these two genes in seedlings and leaves, were able to upregulate their expression in flowers. In the earlier stages of flower development, when ethylene production is very low, the expression of CpCTR1 and CpCTR2 is higher in male floral organs, which agrees with the role of these genes as negative regulators of ethylene signalling, and explain the lower ethylene sensitivity of male flowers in comparison with female flowers. The function of the upregulation of these two genes in later stages of female flower development, when the production of ethylene is also increased, is discussed.
