Jumping gene gs of Lycopersicon lycopersicum (L.) Karsten ex Farw

Studies on tomato culture revealed for the first time two phenomena: (1) instability of gene gs (green stripes on fruits) and (2) spontaneous expression of the character determined by the gs gene without involvement of sexual reproduction in some cultivars. The instability of the gs gene was detected by the phenotypic expression of character in different plants from the same strain, racemes of the same plant, fruits of the same raceme, and parts of the same fruit. The instability of the gs gene may be determined by endogenous regulatory genetic elements causing specific changes of the character, with the degree of these changes varying for different parts of the fruit and places of its formation on the plant. The instability of the gs gene was expressed for four generations. There were no other phenotypic changes in the offsprings studied. In addition, migration of the recessive gs gene to other cultivars followed by its complete expression in a whole plant or some parts of the plant was observed. Exogenous transfer of the gs gene is suggested.     

A multilevel analysis of fruit growth of two tomato cultivars in response to fruit temperature

Fruit phenotype is a resultant of inherent genetic potential in interaction with impact of environment experienced during crop and fruit growth. The aim of this study was to analyze the genetic and physiological basis for the difference in fruit size between a small (‘Brioso’) and intermediate (‘Cappricia’) sized tomato cultivar exposed to different fruit temperatures. It was hypothesized that fruit heating enhances expression of cell cycle and expansion genes, rates of carbon import, cell division and expansion, and shortens growth duration, whereas increase in cell number intensifies competition for assimilates among cells. Unlike previous studies in which whole‐plant and fruit responses cannot be separated, we investigated the temperature response by varying fruit temperature using climate‐controlled cuvettes, while keeping plant temperature the same. Fruit phenotype was assessed at different levels of aggregation (whole fruit, cell and gene) between anthesis and breaker stage. We showed that: (1) final fruit fresh weight was larger in ‘Cappricia’ owing to more and larger pericarp cells, (2) heated fruits were smaller because their mesocarp cells were smaller than those of control fruits and (3) no significant differences in pericarp carbohydrate concentration were detected between heated and control fruits nor between cultivars at breaker stage. At the gene level, expression of cell division promoters (CDKB2, CycA1 and E2Fe‐like) was higher while that of the inhibitory fw2.2 was lower in ‘Cappricia’. Fruit heating increased expression of fw2.2 and three cell division promoters (CDKB1, CDKB2 and CycA1). Expression of cell expansion genes did not corroborate cell size observations.     

Overexpression of yeast spermidine synthase impacts ripening,senescence and decay symptoms in tomato

Polyamines (PAs) are ubiquitous, polycationic biogenic amines that are implicated in many biological processes, including plant growth and development, but their precise roles remain to be determined. Most of the previous studies have involved three biogenic amines: putrescine (Put), spermidine (Spd) and spermine (Spm), and their derivatives. We have expressed a yeast spermidine synthase (ySpdSyn) gene under constitutive (CaMV35S) and fruit‐ripening specific (E8) promoters in Solanum lycopersicum (tomato), and determined alterations in tomato vegetative and fruit physiology in transformed lines compared with the control. Constitutive expression of ySpdSyn enhanced intracellular levels of Spd in the leaf, and transiently during fruit development, whereas E8‐ySpdSyn expression led to Spd accumulation early and transiently during fruit ripening. The ySpdSyn transgenic fruits had a longer shelf life, reduced shriveling and delayed decay symptom development in comparison with the wild‐type (WT) fruits. An increase in shelf life of ySpdSyn transgenic fruits was not facilitated by changes in the rate of water loss or ethylene evolution. Additionally, the expression of several cell wall and membrane degradation‐related genes in ySpdSyn transgenic fruits was not correlated with an extension of shelf life, indicating that the Spd‐mediated increase in fruit shelf life is independent of the above factors. Crop maturity, indicated by the percentage of ripening fruits on the vine, was delayed in a CaMV35S‐ySpdSyn genotype, with fruits accumulating higher levels of the antioxidant lycopene. Notably, whole‐plant senescence in the transgenic plants was also delayed compared with WT plants. Together, these results provide evidence for a role of PAs, particularly Spd, in increasing fruit shelf life, probably by reducing post‐harvest senescence and decay.     

Τhe Role of a Gibberellin 20-Oxidase Gene in Fruit Development in Pepper (Capsicum annuum)

Fruit shape is a very important fruit quality character frequently affected by grafting in vegetable plants like pepper. It has already been shown that, similar to tomato, fruit shape in pepper is likely controlled by an Ovate-like gene, CaOvate, the down-regulation of which positively affects fruit elongation. To further understand the molecular mechanisms involved in pepper fruit shape control and the changes imposed by grafting, we have amplified, sequenced, and structurally characterized CaGA20ox1, the target gene of CaOvate, from a long fruit and a round fruit shaped cultivar. The results show that CaGA20ox1 has similar genomic organization to the tomato GA20ox1 and encodes a 375-amino acid polypeptide that shares 89% identity with tomato GA20ox1. We then studied CaGA20ox1 expression in different pepper plant parts and in different developmental stages of flower and fruit development. The expression of the gene was quantified by means of relative quantitative PCR in the developmental stage of 10?days after anthesis fruit of both cultivars. The results showed that there is a significant difference in the expression of the CaGA20ox1 between the two cultivars in this specific stage as well as in the expression of CaGA20ox1 after virus-induced gene silencing (VIGS) of CaOvate. Finally, the 5?? upstream sequences of CaGA20ox1 gene of the two cultivars were examined and compared. These results corroborate our previous findings, where VIGS of CaOvate alters CaGA20ox1 expression, leading to more elongated fruit, and also progress further the understanding of the genes involved in fruit shape control in pepper opening the way for understanding the molecular means of grafting effects.     

Effects of seasonal temperature changes on <Emphasis Type="Italic">DkMyb4</Emphasis> expression involved in proanthocyanidin regulation in two genotypes of persimmon (<Emphasis Type="Italic">Diospyros kaki</Emphasis> Thunb.) fruit

Persimmon fruits accumulate a large amount of proanthocyanidin (PA). Fruits of the mutant non-astringent (NA) type lose their ability to accumulate PA at an early stage of fruit development, whereas fruits of the normal astringent (A) type sustain PA accumulation until ripening. This allelotype is determined by the genotype of a single ASTRINGENCY (AST) locus. It is possible that the reduction in PA accumulation in NA-type fruits is due to phenological down-regulation of DkMyb4 (a PA regulator) and the resultant down-regulation of structural genes in the PA pathway. In this study, attempts were made to identify the regulatory mechanisms of phenological PA accumulation in A- and NA-type fruits, focusing particularly on the effects of ambient temperature. Continuous cool temperature conditions caused sustained expression of DkMyb4 in NA-type fruits, as well as in A-type fruits, resulting in increased expression of PA pathway genes and PA accumulation. However, the expression of some A/NA phenotypic marker genes was not significantly affected by the cool temperature conditions. In addition, PA composition in NA-type fruits exposed to cool temperatures differed from that in A-type fruits. These results indicate that a cool ambient temperature may have induced DkMyb4 expression and resultant PA accumulation, but did not directly affect the expression of the AST gene.     

Parallel Evolution Under Domestication and Phenotypic Differentiation of the Cultivated Subspecies of <Emphasis Type="Italic">Cucurbita pepo</Emphasis> (Cucurbitaceae)

Parallel Evolution under Domestication and Phenotypic Differentiation of the Cultivated Subspecies of Cucurbita pepo (Cucurbitaceae). Cucurbita pepo (pumpkin, squash, gourd, Cucurbitaceae) is an ancient North American domesticate of considerable economic importance. Based on molecular genetic polymorphisms, two cultivated lineages of this species, each consisting of very many edible–fruited cultigens, have been recognized, C. pepo subsp. pepo and C. pepo subsp. texana. However, the phenotypic commonalities and differences between these two subspecies have not as yet been systematically collected and organized. Among the evolutionary developments common to the two subspecies are the increased size of the plant parts, less plant branching, and premature loss of chlorophyll in the exocarp of the fruits. In both subspecies, bush growth habit, conferred by allele Bu, is common to the cultigens grown for consumption of the immature fruits, as is the deviation from the 1:1 ratio of fruit length to fruit width. A major characteristic differentiating between the edible–fruited cultigens of the respective subspecies are the longitudinal protrusions, in subsp. pepo, versus depressions, in subsp. texana, of the fruit surface corresponding with the subsurface primary carpellary vein tracts. Subsp. pepo also has larger fruits and larger and longer seeds. In addition, some alleles affecting stem color, leaf mottling, multiple flower bud production, and fruit characteristics are frequently occurring to nearly fixed in one subspecies but are rare to less common in the other.     

White-fruited Duchesnea indica (Rosaceae) is impaired in ANS gene expression

? Premise of the study: Duchesnea indica is a wild strawberry-like species that has red fruits. In a recent survey in the highlands of Tucumán (Argentina), a plant of D. indica with white fruits was discovered. The aim of this study was to investigate whether the white-fruited character was due to a phenotypic or genotypic change. The stability and heritability of the character and the expression of genes involved in anthocyanins synthesis were studied and compared with red-fruited genotypes. This study contributes to understanding the molecular basis of some factors involved in fruit pigmentation, a horticulturally and taxonomically important trait. ? Methods: Stability and heritability of the white-fruited character were evaluated in plants obtained by asexual propagation or by sexual crosses between the white- and red-fruited genotypes. Asexual multiplications were carried out by stolon rooting and sexual multiplications by germination of achenes obtained from crosses. The expression level of the genes involved in the synthesis and regulation of the anthocyanins pathway (CHS, F3H, DFR, ANS, and MYB10) were evaluated by RT-PCR using specific primers. ? Key results: Plants with the white-fruited character always yielded white-fruited progeny when propagated asexually, whereas in sexually propagated plants fruit color depended on the mother. Red-fruited mothers yielded red-fruited progeny, and white-fruited mothers yielded fruits ranging from dark pink to white. Molecular analysis suggested that the white-fruited character was due to the low expression of the ANS gene. ? Conclusions: Results obtained indicate that the white-fruited character was stable. Mother progenitors exert a strong influence on the expression of the white-fruited character. The white-fruited phenotype is due to the impairment or downregulation of the ANS gene.     

Variability and correlations in muskmelon in relation to the cultivation method

Summary Six fruit characters have been measured in 23 cultivars of Cucumis melo, representing a wide geographical range. Plants were grown both in the greenhouse and in the field. When the 23 cultivars were analyzed together, the largest component of variance was found between cultivars under both growth conditions, suggesting the existence of large genetic diversity for all the characters studied. Generally, variance between plants within cultivars was less than or equal to variance between fruits within plant. This indicates that environmental variation is the most important part of the variation within cultivars. Correlations between pairs of characters at cultivar, plant and fruit levels were calculated from the variance-covariance components. In the majority of paired traits, the correlation values indicated that genetic and environmental factors may act in the same direction.     

Blossom-end rot in relation to growth rate and calcium content in fruits of sweet pepper (Capsicum annuum L.)

The relative importance of growth rate and calcium concentration in sweet pepper fruits (Capsicum annuum L.) for the induction of blossom-end rot (BER) was investigated in (1) four pollination treatments in one cultivar, (2) four cultivars with the same fruit load and (3) three fruit load treatments in four cultivars. For fruits with the same pollination treatment those eventually developing BER had a higher initial fruit growth rate than those not developing BER. Within the same experiment both the growth rate of the young fruit and BER increased with the number of seeds. The Ca concentration of the pericarp in mature fruits was negatively related to both fruit size and BER incidence. Differences in levels of BER between different pollination experiments could not be explained solely by differences in growth rate of the young fruit, but related to different Ca concentrations in the mature fruits. In the spring, but not in the summer, cultivars more susceptible to BER had a larger final size but lower Ca concentration in the young fruit than the resistant ones. By lowering the fruit load in the summer both the final fruit size and the BER incidence increased, but the Ca concentrations of both proximal and distal pericarp in the young fruit of all cultivars were not consistently affected. Despite a correlation between growth rate and low Ca concentration in the fruit, the incidence of BER may only be predicted from separate effects of fruit growth and of Ca concentration of fruit. The data indicated that at a higher growth rate a higher Ca concentration is required to prevent the induction of BER. The usefulness of the total Ca concentration of the fruit for determining the critical Ca concentration in the induction of BER is discussed.Key words: Capiscum annuum L., sweet pepper, blossom-end rot, calcium, growth rate, pollination, fruit load.      

The cell size distribution of tomato fruit can be changed by overexpression of CDKA1

Tomato is one of the most cultivated vegetables in the world and an important ingredient of the human diet. Tomato breeders and growers face a continuous challenge of combining high quantity (production volume) with high quality (appearance, taste and perception for the consumers, processing quality for the processing industry). To improve the quality of tomato, it is important to understand the regulation of fruit development and of fruit cellular structure, which is in part determined by the sizes and numbers of cells within a tissue. The role of the cell cycle therein is poorly understood. Plant cyclin‐dependent kinases (CDKs) are homologues of yeast cdc2, an important cell cycle regulator conserved throughout all eukaryotes. CDKA1 is constitutively expressed during the cell cycle and has dual functions in S‐ and M‐phase progression. We have produced transgenic tomato plants with increased expression of CDKA1 under the control of the fruit‐specific TPRP promoter, which despite a reduced number of seeds and diminished amount of jelly, developed fruits with weight and shape comparable to that of wild‐type fruits. However, the phenotypic changes with regard to the pericarp thickness and placenta area were remarkable. Fruits of tomato plants with the highest expression of CDKA1 had larger septa and columella (placenta), compared with wild‐type fruits. Our data demonstrate the possibility of manipulating the ratio between cell division and expansion by changing the expression of a key cell cycle regulator and probably its activity with substantial effects on structural traits of the harvested fruit.     

Graft-induced genetic changes and the inheritance of several characteristics in pepper (Capsicum annuum L.)

 The general characteristics of several graft-induced changes in pepper were investigated in a cross experiment. F₁, F₂, and BC₁ progenies derived from crosses of the original stock and scion cultivars ‘Spanish Paprika’ and ‘Yatsubusa’, respectively, as well as their graft-induced variant strain G₅S₂₅ were analyzed for inheritance of the most conspicuous graft-induced variant traits. As part of a research program with the aim of revealing the mechanism of graft induction, the present study was carried out to examine the stability of the phenotypic changes and the characteristics of the graft-induced variants. For the fruit apex, a two-gene system was suggested, with other factors having a modifying influence. One of the two apex genes acted for pointed fruits and the other for inverted-blunt fruits. The inverted-blunt gene, the apex gene of the stock, was unambiguously present in the graft-induced variants, while the pointed gene that acted in the dominant mode in the original scion was inactive and expressed only under certain conditions in a mosaic state. The stable inverted-blunt cultivar used for the stock maintained certain factor(s) for pointed fruit, but the presence of that factor(s) could not be detected in graft-induced variants. The results of pungency analysis suggested a gene for non-pungency that appeared to be introduced in the graft-induced variants. The fruiting habit and fruiting direction that appeared in a mosaic state in graft-induced variants were found to combine factors of the stock with the appropriate characteristics of the scion asymmetrically. The bushy plant type appeared in a transgressive state in the variants, showing a definitely higher number of branches on the main stem and more frequent ramifications on the complete plant than on either the stock and scion cultivars or the progency derived from sexual crosses. A change in mature fruit color from red to yellow occurred in an early generation of graft-induced variants. Our results demonstrate that some of the characteristics of the stock were introduced into the progeny obtained from selfed seeds of the scion and that novel characteristics appeared as a result of graft induction. Received: 30 December 1997 / Accepted: 3 March 1998     

Involvement of Epicatechin in Cultivar Susceptibility of Avocado Fruits to Colletotrichum gloeosporioides after Harvest1

Avocado cultivars were defined as susceptible and resistant to Colletotrichum gloeosporioides depending upon the length of the incubation period of the disease after fruit softening. In the susceptible cultivars Fuerte, Horshim, Vurtz, Rincon, and Benik, epicatechin concentration of the peel decreased to 60-130 μg.g^?1, fr. wt. at fruit softening and symptoms appeared on the same or one day later. In the resistant cultivars Hass, Nabal, Netaim and Pinkerton, epicatechin concentration was still 632–1740 μg.g^?1 fr. wt. when fruit softening and symptoms appeared only 4-10 days later. When susceptible Fuerte fruits became soft the concentration of the antifungal compound 1-acetoxy-2-hydroxy-4-oxo-heneicosa-12,15 diene, had decreased to 120 μg.g^?1 fr. wt. and symptoms appeared. In resistant Hass fruits, the antifungal diene was still 238 μg.g^?1 fr. wt. at fruit softening; and it had further decreased to 159 μg.g^?1 fr. wt. when symptoms appeared, four days later. A modified atmosphere and 0.2 M CaCl₂ infiltration both delayed softening of Fuerte fruits; but symptom appearance on these fruits was related to diene decrease and not to fruit softening. The results are discussed in relation to the hypothesis that the susceptibility of avocado cultivars to post-harvest decay by C. gloeosporioides is related to the degradation of the antifungal diene, catalyzed by avocado lipoxygenase, the activity of which is regulated by the decline of its inhibitor epicatechin.     

Exploring the limiting causes of fruit production in the tropical tree Ipomoea wolcottiana Rose (Convolvulaceae)

Path analysis was used to evaluate a group of variables related to fruit production in the tropical tree Ipomoea wolcottiana (Convolvulaceae). The variables were tree size (trunk diameter), available phosphorus in the soil, floral phenotypic sex expression (i.e. gynoecium biomass allocation), flower production, fruits initiated, and length of the corolla and diameter of its opening. The path model explained 79.9% of the total variation, and the production of mature fruits was related in large part by the number of fruits initiated and by phenotypic sex expression. In turn, fruits initiated were related to corolla tube diameter and to a lesser extent to corolla tube length. The model could explain a low percentage of the variation (18.5%) of the number of fruits initiated, but once a fruit was initiated it had a high probability of maturing. Phenotypic sex expression related negatively to the number of flowers produced and positively, to almost the same degree, to available phosphorus in the soil. Tree size had a positive effect on flower production but a negligible effect on fruits initiated and matured. Soil phosphorus affected positively, although weakly all variables. The relationships between tree size, number of flowers and phenotypic sex expression suggested that abundant flowering in this species functions more for pollen donation than its reception.