Early Stages Of Fruit Development Research Articles

Four novel Cit7GlcTs functional in flavonoid 7-O-glucoside biosynthesis are vital to flavonoid biosynthesis shunting in citrus

Abstract Citrus fruits have abundant flavonoid glycosides (FGs), an important class of natural functional and flavor components. However, there have been few reports about the modification of UDP-glycosyltransferases (UGTs) on flavonoids in citrus. Notably, in flavonoid biosynthesis, 7-O-glucosylation is the initial and essential step of glycosylation prior to the synthesis of flavanone disaccharides, the most abundant and iconic FGs in citrus fruits. Here, based on the accumulation of FGs observed at the very early fruit development stage of two pummelo varieties, we screened six novel flavonoid 7-O-glucosyltransferase genes (7GlcTs) via transcriptomic analysis and then characterized them in vitro. The results revealed that four Cg7GlcTs possess wide catalytic activities towards various flavonoid substrates, with CgUGT89AK1 exhibiting the highest catalytic efficiency. Transient overexpression of CgUGT90A31 and CgUGT89AK1 led to increases in FG synthesis in pummelo leaves. Interestingly, these two genes had conserved sequences and consistent functions across different germplasms. Moreover, CitUGT89AK1 was found to play a role in the response of citrus to Huanglongbing infection by promoting FG production. The findings improve our understanding of flavonoid 7-O-glucosylation by identifying the key genes, and may help improve the benefits of flavonoid biosynthesis for plants and humans in the future.

Cytological characteristics of blueberry fruit development

Using the blueberry cultivar "Powderblue" after pollination, fruits at different developmental stages were collected for study. The transverse and longitudinal diameters, individual fruit weight, and fruit water content were measured during their development. Employing tissue sectioning and microscopy techniques, we systematically studied the morphological features and anatomical structures of the fruits and seeds at various developmental stages, aiming to elucidate the cytological patterns during blueberry fruit development. The results of our study revealed that the "Powderblue" blueberry fruit growth and development followed a double "S" curve. Mature "Powderblue" blueberries were blue-black in color, elliptical in shape, with five locules, an inferior ovary, and an average fruit weight of 1.73 ± 0.17 g, and a moisture content of 78.865 ± 0.9%. Blueberry fruit flesh cells were densely arranged with no apparent intercellular spaces, and mesocarp cells accounted for 52.06 ± 7.4% of fruit cells. In the early fruit development stages, the fruit flesh cells were rapidly dividing, significantly increasing in number but without greatly affecting the fruit's morphological characteristics. During the later stages of fruit development, the expansion of the fruit flesh cells became prominent, resulting in a noticeable increase in the fruit's dimensions. Except for the epidermal cells, cells in all fruit tissues showed varying degrees of rupture as fruit development progressed, with the extent of cell rupture increasing, becoming increasingly apparent as the fruit gradually softened. Additionally, numerous brachysclereids (stone cells) appeared in the fruit flesh cells. Stone cells are mostly present individually in the fruit flesh tissue, while in the placental tissue, they often group together. The "Powderblue" blueberry seeds were light brown, 4.13 ± 0.42 mm long, 2.2 ± 0.14 mm wide, with each fruit containing 50–60 seeds. The "Powderblue" seeds mainly consisted of the seed coat, endosperm, and embryo. The embryo was located at the chalazal end in the center of the endosperm and was spatially separated. The endosperm, occupying the vast majority of the seed volume, comprised both the chalazal and outer endosperm, and the endosperm developed and matured before the embryo. As the seed developed, the seed coat was gradually lignified and consisted of palisade-like stone cells externally and epidermal layer cells internally.

Calcium absorption by fruit and leaves of sweet cherry trees (Prunus avium L.) by isotope labeling

In sweet cherry, foliar Calcium–based products are used to mitigate rain–cracking in fruit and to improve its firmness during storage. Information on foliar Calcium (Ca) absorption efficiency by fruit and leaves in the field is scarce. In part, this is due to the limitations of the traditional analytical techniques for assessing Ca levels in these organs. Here, we hypothesize that leaves and fruit differ in their abilities to uptake surface applications of Ca and, moreover, that their abilities are influenced by phenology. To test this hypothesis, foliar 44Ca (0.05% 44CaCl2) was used to enrich sweet cherry fruit and leaves of the combination ‘Lapins’/‘Colt’ during the 2019–2020 growing season in the Central Valley of Chile (34° 0’ S, 71° 41’ W). Six treatments were applied, represented by different timings (days after full bloom, DAFB) of isotopic labeling of either fruit or leaves. Labeling was applied at Stage I, SII and SIII of fruit development. Fruit or leaves were ‘painted’ with 44CaCl2 (0.05%, 97 atom%) using a brush. Each labeling date considered a different group of similar fruiting spurs on the two-year-old wood of individual vertical branches. Additional samples were collected to measure natural abundance of 44Ca. Labeled fruit were removed 48 h after aerial 44Ca enrichment and at harvest (87 DAFB).Uptake of 44Ca by fruit and leaves was observed throughout the period of fruit development. Fruiting spur leaves (FSL) and fruit absorbed 44CaCl2 and were highly enriched 48 h after labeling. The earlier the labeling date, the higher the 44Ca tracer recovery detected in both organs. However, FSL showed higher δ44Ca ‰, 44Ca concentrations and 44Ca contents than fruit during the whole period of fruit development. After 48 h, the aerial uptake at SI (expressed as δ44Ca ‰) was 3.4 times higher in immature FSL and 5.7 times higher in immature fruit than SIII of fruit development, which indicates that Ca sprays should start soon after fruit set. We conclude that in sweet cherry, foliar Ca is absorbed by fruit and spur leaves, but the absorption is more efficient in the early stages of fruit development and for young leaves.

Genome-wide identification of the CONSTANS-LIKE (COL) family and mechanism of fruit senescence regulation by PpCOL8 in sand pear (Pyrus pyrifolia)

Pyrus pyrifolia Nakai ‘Whangkeumbae’ is a sand pear fruit with excellent nutritional quality and taste. However, the industrial development of pear fruit is significantly limited by its short shelf life. Salicylic acid (SA), a well-known phytohormone, can delay fruit senescence and improve shelf life. However, the mechanism by which SA regulates CONSTANS-LIKE genes (COLs) during fruit senescence and the role of COL genes in mediating fruit senescence in sand pear are poorly understood. In this study, 22 COL genes were identified in sand pear, including four COLs (PpCOL8, PpCOL9a, PpCOL9b, and PpCOL14) identified via transcriptome analysis and 18 COLs through genome-wide analysis. These COL genes were divided into three subgroups according to the structural domains of the COL protein. PpCOL8, with two B-box motifs and one CCT domain, belonged to the first subgroup. In contrast, the other three PpCOLs, PpCOL9a, PpCOL9b, and PpCOL14, with similar conserved protein domains and gene structures, were assigned to the third subgroup. The four COLs showed different expression patterns in pear tissues and were preferentially expressed at the early stage of fruit development. Moreover, the expression of PpCOL8 was inhibited by exogenous SA treatment, while SA up-regulated the expression of PpCOL9a and PpCOL9b. Interestingly, PpCOL8 interacts with PpMADS, a MADS-box protein preferentially expressed in fruit, and SA up-regulated its expression. While the production of ethylene and the content of malondialdehyde (MDA) were increased in PpCOL8-overexpression sand pear fruit, the antioxidant enzyme (POD and SOD) activity and the expression of PpPOD1 and PpSOD1 in the sand pear fruits were down-regulated, which showed that PpCOL8 promoted sand pear fruit senescence. In contrast, the corresponding changes were the opposite in PpMADS-overexpression sand pear fruits, suggesting that PpMADS delayed sand pear fruit senescence. The co-transformation of PpCOL8 and PpMADS also delayed sand pear fruit senescence. The results of this study revealed that PpCOL8 can play a key role in pear fruit senescence by interacting with PpMADS through the SA signaling pathway.

Comparative transcriptome analysis revealed that auxin and cell wall biosynthesis play important roles in the formation of hollow hearts in cucumber

BackgroundHollow heart is a kind of physiological defect that seriously affects the yield, quality, and economic value of cucumber. However, the formation of hollow hearts may relate to multiple factors in cucumber, and it is necessary to conduct analysis.ResultsIn this study, hollow and non-hollow fruits of cucumber K07 were used for comparative transcriptome sequencing and analysis. 253 differentially expressed genes and 139 transcription factors were identified as being associated with the formation of hollow hearts. Hormone (auxin) signaling and cell wall biosynthesis were mainly enriched in GO and KEGG pathways. Expression levels of key genes involved in indole-3-acetic acid biosynthesis in carpel were lower in the hollow fruits than non-hollow fruits, while there was no difference in the flesh. The concentration of indole-3-acetic also showed lower in the carpel than flesh. The biosynthetic pathway and content analysis of the main components of the cell wall found that lignin biosynthesis had obvious regularity with hollow heart, followed by hemicellulose and cellulose. Correlation analysis showed that there may be an interaction between auxin and cell wall biosynthesis, and they collectively participate in the formation of hollow hearts in cucumber. Among the differentially expressed transcription factors, MYB members were the most abundant, followed by NAC, ERF, and bHLH.ConclusionsThe results and analyses showed that the low content of auxin in the carpel affected the activity of enzymes related to cell wall biosynthesis at the early stage of fruit development, resulting in incomplete development of carpel cells, thus forming a hollow heart in cucumber. Some transcription factors may play regulatory roles in this progress. The results may enrich the theory of the formation of hollow hearts and provide a basis for future research.

MODELING OF APPLE CHEMICAL FRUIT THINNING

Crop load management in intensive apple orchards must be done precisely to produce a high yield with marketable fruit size. It also ensures the formation of flower buds on the tree for the next season and prevents alternative bearing. In addition to pruning, flower and fruit thinning is another management method that has a major impact on crop yield. Compared to other methods, chemical thinning is the cheapest, can be done quickly and allows fruit thinning at the right time, which guarantees better fruit quality. The decision on the type of chemical agent, concentration and timing of application is very complex and depends on the apple variety, flowering intensity and fruit growth phase, weather conditions during treatment and a few days after. Flower thinning is applied to very high-yielding varieties where fruit thinning is very difficult and tends to bear alternately. Ammonium thiosulphate or ethephon can be used for this purpose only in years with abundant flowering and in conditions where there is no risk of spring frosts. Regardless of whether flower thinning has been carried out or not, the fruits are chemically thinned in the period shortly after flowering. The usual chemical treatment(s) is (are) applied at the early stage of fruit development, when the diameter of the central fruits in a cluster on 2-year-old wood is 5 to 16 mm (in exceptional cases up to 20 mm). At this time, naphthalene acetamide (NAD), naphthalene acetic acid (NAA), 6-benzyladenine (6- BA), and metamitron are used to induce abscission of young fruit. These chemicals are used alone or in various combinations to improve the effect. If the thinning efficacy of the single application is weak, sequential applications of chemical thinners with different modes of action must be made 1-3 weeks after the previous application to reduce fruit set to a commercially acceptable level. To avoid under- or over-thinning of fruit of a particular variety, models that predict the effectiveness of chemicals based on short-term light and temperature forecasts are used to determine the optimal time to apply thinners. Immediately after the first application of thinning agents, the “fruit growth rate model” can be used for early assessment of apple tree response to thinning and the need for a new application.

Time course of changes in the transcriptome during russet induction in apple fruit

BackgroundRusseting is a major problem in many fruit crops. Russeting is caused by environmental factors such as wounding or moisture exposure of the fruit surface. Despite extensive research, the molecular sequence that triggers russet initiation remains unclear. Here, we present high-resolution transcriptomic data by controlled russet induction at very early stages of fruit development. During Phase I, a patch of the fruit surface is exposed to surface moisture. For Phase II, moisture exposure is terminated, and the formerly exposed surface remains dry. We targeted differentially expressed transcripts as soon as 24 h after russet induction.ResultsDuring moisture exposure (Phase I) of ‘Pinova’ apple, transcripts associated with the cell cycle, cell wall, and cuticle synthesis (SHN3) decrease, while those related to abiotic stress increase. NAC35 and MYB17 were the earliest induced genes during Phase I. They are therefore linked to the initial processes of cuticle microcracking. After moisture removal (Phase II), the expression of genes related to meristematic activity increased (WOX4 within 24 h, MYB84 within 48 h). Genes related to lignin synthesis (MYB52) and suberin synthesis (MYB93, WRKY56) were upregulated within 3 d after moisture removal. WOX4 and AP2B3 are the earliest differentially expressed genes induced in Phase II. They are therefore linked to early events in periderm formation. The expression profiles were consistent between two different seasons and mirrored differences in russet susceptibility in a comparison of cultivars. Furthermore, expression profiles during Phase II of moisture induction were largely identical to those following wounding.ConclusionsThe combination of a unique controlled russet induction technique with high-resolution transcriptomic data allowed for the very first time to analyse the formation of cuticular microcracks and periderm in apple fruit immediately after the onset of triggering factors. This data provides valuable insights into the spatial-temporal dynamics of russeting, including the synthesis of cuticles, dedifferentiation of cells, and impregnation of cell walls with suberin and lignin.

Ethylene Signaling Pathway Genes in Strawberry and Their Expression Patterns during Fruit Ripening

Ethylene at least partly regulates some aspects during non-climacteric ripening in strawberry. However, the ethylene signaling pathway genes in the strawberry fruit have not been comprehensively and systematically analyzed. In the present study, 15 FaETRs and 14 FaEIN3/EINs were identified in the octoploid strawberry genome. Subcellular localization analysis predicted that FaETRs and FaEIN3/EINs are respectively localized to the endoplasmic reticulum and the nucleus. The phylogenetic trees showed that FaETRs were classified into two subgroups, while FaEIN3/EINs were divided into three clades, which was supported by gene structure and conserved motif analysis. FaETRs and FaEIN3/EINs could interact with several components, such as CTR1, RTE1, EIN2 and ERF1B, in the ethylene signaling pathway by protein–protein interaction network analysis. Transcriptomic data showed that FaETRs were mainly expressed at the early stage of fruit development in three strawberry cultivars. Additionally, a couple of FaETRs (FaETR2 and FaETR13) and FaEINs (FaEIN2 and FaEIN7) could be induced by 1 μM ABA and inhibited by 100 μM nordihydroguaiaretic acid (NDGA, an ABA biosynthesis blocker). These findings suggested that the FaETR- and FaEIN3/EIN-mediated ethylene signaling pathway might play a role in strawberry fruit ripening.

Incidence and Severity of Blister Mite (Eriophyes erinea Nalepa) on Walnut (Juglans regia L.) under Temperate Conditions of Kashmir Valley

Walnut is an important crop that is widely grown for its edible nuts, timber, and other commercial uses. Walnut pests can cause significant damage to the trees and reduce the quality and quantity of the crop. Walnut blister beetles can cause significant damage to walnut trees, especially during the early stages of fruit development. The data generated on incidence and severity revealed that the incidence of E. erinea commenced from 13th standard meteorological week (SMW) with mean incidence of 1.2 blister per leaf observed in this SMW, reached to its peak (22.7 per leaf) during 30th SMW and then decreased and reached to 0.8 blisters per leaf during 43rd SMW. The mean number of blister was found highest (18.64±1.62) in the month of July and lowest (1.25±0.2) in the month of October. Low severity (4.0%) of E. erinea was recorded in April, which reached to its peak (28.5%) in the month of July, thereafter, the severity decreased and reached to 1.5 per cent in the month of October.

Investigation of current status and disease progress of bronzing on “Thai” jackfruit (Artocarpus heterophyllus Lam.) in Tien Giang province

Tien Giang is one of the Mekong Delta's largest jackfruit-growing provinces, with a total cultivation area of jackfruit of approximately 13,141.09 ha. Bronzing of jackfruit appeared on Thai jackfruit and caused significant damage to growers, however, the information about the disease is still limited. In this study, we assessed the status of bronzing diseases on Thai jackfruit in Tien Giang province via direct interviews with farmers, mapped the disease distribution by Google Earth, and recorded the disease appearance on Thai jackfruit during the year's two main seasons. Bronzing of Thai jackfruit occurred in all growing areas in Tien Giang during both rainy and sunny seasons, causing damage with an average disease prevalence in inquired regions from 5.29% to 10.19% in sunny season, and from 25.43% to 33.05% in rainy season. The disease prevalence was higher in the rainy season. Most farmers showed that bronzing of jackfruit could be identified by external symptoms of the fruit, such as abnormalities in the left stalk, fruit color, shape, and spines, and confirmed by the result of appearance investigation of bronzing on Thai jackfruit during rainy and sunny seasons of the year 2022. Fungicide application and fruit selection at the early stage of fruit development could prevent the disease. According to the disease progress, bronzing of jackfruit appeared from fruit set to harvest and the disease prevalence reached 55.56% in sunny season and 88.89% in rainy season at 20 days after fruit set.

A multifunctional true caffeoyl coenzyme A O-methyltransferase enzyme participates in the biosynthesis of polymethoxylated flavones in citrus.

Polymethoxylated flavones (PMFs) have received extensive attention due to their abundant bioactivities. Citrus peels specifically accumulate abundant PMFs, and methylation modification is a key step in PMF biosynthesis; however, the function of reported O-methyltransferase (OMT) in citrus is insufficient to elucidate the complete methylation process of PMFs. In this study, we analyzed the accumulation pattern of PMFs in the flavedo of the sweet orange (Citrus sinensis) cultivar "Bingtangcheng" at different developmental stages. We found that accumulation of PMFs was completed at the early stage of fruit development (60-d after flowering). Furthermore, we characterized a true caffeoyl-CoA O-methyltransferase (named CsCCoAOMT1) from C. sinensis. Functional analysis in vitro showed that CsCCoAOMT1 preferred flavonoids to caffeoyl-CoA and esculetin. This enzyme efficiently methylated the 6-, 7- 8-, and 3'-OH of a wide array of flavonoids with vicinal hydroxyl groups with a strong preference for quercetin (flavonol) and flavones. The transient overexpression and virus-induced gene silencing experiments verified that CsCCoAOMT1 could promote the accumulation of PMFs in citrus. These results reveal the function of true CCoAOMTs and indicate that CsCCoAOMT1 is a highly efficient multifunctional O-methyltransferase involved in the biosynthesis of PMFs in citrus.

Comparative Characteristics of Genes 9-Cis-Epoxycarotinoid-Dioxygenase SlNCED1 and SlNCED2 during the Development

Tomato Solanum lycopersicum L. is an important agricultural crop and, at the same time, a model for studying the ontogeny of the succulent fruit. The decisive role in the ripening of the fruit is played by abscisic acid, which is formed as a result of the oxidative cleavage of epoxycarotenoids 9-cis-epoxycarotenoid dioxygenases NCED. Gene-expression profiles of SlNCED1 and SlNCED2 and the content of carotenoids in fruits at different stages of development were determined in three varieties of tomato with different color of ripe fruit. It was shown that transcripts of both genes are present in all organs. Transcript level of SlNCED1 was approximately four to six times higher than the level of SlNCED2 transcripts; peak activity of SlNCED1 occurs in the late stages of ripening, while that of SlNCED2 is at the initial stage. Ripe fruits are characterized by the highest amount of carotenoids; lycopene was found only in the fruits of late stages in red-fruited varieties, the highest content of -carotene was found in ripe fruits of the yellow-fruited variety. The precursor of abscisic acid, violaxanthin, is present only in the immature fruit; the other precursor, neoxanthin, decreases with ripening and is absent at the ripeness stage. In red-fruited varieties, a correlation was found between the level of SlNCED1 and SlNCED2 transcripts with the content of -carotene. Findings suggest the coparticipation of SlNCED1 and SlNCED2 in the biosynthesis of abscisic acid during the development and ripening of tomato fruit. In this case, the key role belongs to the gene SlNCED1, the peak of activity of which falls on the stage of changing the color of the fruit. Lower levels of SINCED2 transcripts and its peak activity in the early stages of fruit development suggests a division of NCED functions between the two enzymes.

Transcriptome Analysis Reveals the Genes Related to Water-Melon Fruit Expansion under Low-Light Stress

Watermelon is one of people's favorite fruits globally. Fruit size is one of the important characteristics of fruit quality. Low light can seriously affect fruit development, but there have been no reports concerning molecular mechanism analysis in watermelons involved in fruit expansion under low-light stress. To understand this mechanism, the comparative transcriptomic file of watermelon fruit flesh at four different developmental stages under different light levels was studied. The results showed that the fruit size and content of soluble sugar and amino acids at low-light stress significantly decreased compared to the control. In addition, 0-15 DAP was the rapid expansion period of watermelon fruit affected by shading. In total, 8837 differentially expressed genes (DEGs) were identified and 55 DEGs were found to play a role in the four different early fruit development stages. We also found that genes related to oxidation-reduction, secondary metabolites, carbohydrate and amino acid metabolism and transcriptional regulation played a key role in watermelon fruit expansion under low-light stress. This study provides a foundation to investigate the functions of low-light stress-responsive genes and the molecular mechanism of the effects of low-light stress on watermelon fruit expansion.

Genome-wide identification and molecular characterization of the AP2/ERF superfamily members in sand pear (Pyrus pyrifolia)

Background‘Whangkeumbae’ (Pyrus pyrifolia) is a typical climacteric fruit variety of sand pear with excellent taste. However, the rapid postharvest ethylene production limits the shelf life of ‘Whangkeumbae’ fruit. AP2/ERF superfamily is a large family of transcription factors involved in plant growth and development, including fruit ripening and senescence through the ethylene signaling pathway. The numbers and functions of AP2/ERF superfamily members in sand pear remain largely unknown.ResultsIn this study, a total of 234 AP2/ERF family members were identified through the transcriptome of Pyrus pyrifolia ‘Whangkeumbae’ (17 genes) and Pyrus pyrifolia genome (223 genes) analyses. Six genes (Accession: EVM0023062.1, EVM0034833.1, EVM0027049.1, EVM0034047.1, EVM0028755.1, EVM0015862.1) identified via genome analysis shared 100% identity with PpERF14-L, PpERF5-L, PpERF3a, PpERF3, PpERF017 and PpERF098, respectively, which were identified from transcriptome sequencing. Further, the AP2/ERF superfamily members were divided into AP2, ERF, and RAV subfamilies, each comprising 38, 188, and 8 members, respectively. Tissue-specific expression analysis showed that PpERF061, PpERF113, PpERF51L-B, PpERF5-L, and PpERF017 were predominantly expressed in fruits than in other tissues. Additionally, PpERF5-L and PpERF017 showed higher expressions at the early stage of fruit development. While, PpERF51B-L exhibited higher expression during the fruit ripening stage. Besides, PpERF061 and PpERF113 had pronounced expressions during fruit senescence.ConclusionThese results indicate that PpERF061, PpERF113, PpERF51L-B, PpERF5-L, and PpERF017 could play crucial roles in sand pear fruit development, ripening, and senescence. Overall, this study provides valuable information for further functional analysis of the AP2/ERF genes during fruit ripening and senescence in sand pear.

Propiconazole-induced brassinosteroid deficiency reduces female fertility by inhibiting female gametophyte development in woodland strawberry.

In woodland strawberry, a brassinosteroid biosynthesis inhibitor propiconazole induced typical brassinosteroid-deficient phenotypes and decreased female fertility due to attenuated female gametophyte development. Brassinosteroids (BRs) play roles in various aspects of plant development. We investigated the physiological roles of BRs in the woodland strawberry, Fragaria vesca. BR-level-dependent phenotypes were observed using a BR biosynthetic inhibitor, propiconazole (PCZ), and the most active natural BR, brassinolide (BL). Endogenous BL and castasterone, the active BRs, were below detectable levels in PCZ-treated woodland strawberry. The plants were typical BR-deficient phenotypes, and all phenotypes were restored by treatment with BL. These observations indicate that PCZ is an effective inhibitor of BR in woodland strawberry. Only one gene for each major step of BR biosynthesis in Arabidopsis is encoded in the woodland strawberry genome. BR biosynthetic genes are highly expressed during the early stage of fruit development. Emasculated flowers treated with BL failed to develop fruit, implying that BR is not involved in parthenocarpic fruit development. Similar to BR-deficient and BR-insensitive Arabidopsis mutants, female fertility was lower in PCZ-treated plants than in mock-treated plants due to failed attraction of the pollen tube to the ovule. In PCZ-treated plants, expression of FveMYB98, the homologous gene for Arabidopsis MYB98 (a marker for synergid cells), was downregulated. Ovules were smaller in PCZ-treated plants than in mock-treated plants, and histological analysis implied that the development of more than half of female gametophytes was arrested at the early stage in PCZ-treated plants. Our findings explain how BRs function during female gametophyte development in woodland strawberry.

Characterization of Transcriptome Dynamics during Early Fruit Development in Olive (Olea europaea L.).

In the olive (Olea europaea L.), an economically leading oil crop worldwide, fruit size and yield are determined by the early stages of fruit development. However, few detailed analyses of this stage of fruit development are available. This study offers an extensive characterization of the various processes involved in early olive fruit growth (cell division, cell cycle regulation, and cell expansion). For this, cytological, hormonal, and transcriptional changes characterizing the phases of early fruit development were analyzed in olive fruit of the cv. 'Picual'. First, the surface area and mitotic activity (by flow cytometry) of fruit cells were investigated during early olive fruit development, from 0 to 42 days post-anthesis (DPA). The results demonstrate that the cell division phase extends up to 21 DPA, during which the maximal proportion of 4C cells in olive fruits was reached at 14 DPA, indicating that intensive cell division was activated in olive fruits at that time. Subsequently, fruit cell expansion lasted as long as 3 weeks more before endocarp lignification. Finally, the molecular mechanisms controlling the early fruit development were investigated by analyzing the transcriptome of olive flowers at anthesis (fruit set) as well as olive fruits at 14 DPA (cell division phase) and at 28 DPA (cell expansion phase). Sequential induction of the cell cycle regulating genes is associated with the upregulation of genes involved in cell wall remodeling and ion fluxes, and with a shift in plant hormone metabolism and signaling genes during early olive fruit development. This occurs together with transcriptional activity of subtilisin-like protease proteins together with transcription factors potentially involved in early fruit growth signaling. This gene expression profile, together with hormonal regulators, offers new insights for understanding the processes that regulate cell division and expansion, and ultimately fruit yield and olive size.

Tomato STEROL GLYCOSYLTRANSFERASE 1 silencing unveils a major role of steryl glycosides in plant and fruit development

Free and glycosylated sterols localize in the plant cell plasma membrane, where in combination with other lipids regulate its structure and function. The role of glycosylated sterols in regulating membrane-associated biological processes is more relevant in plants like tomato (Solanum lycopersicum), in which glycosylated sterols are the predominant sterols. A proper ratio of free sterols versus glycosylated sterols has proven to be essential for proper plant performance in several species, but almost nothing is known in tomato. To assess the role of glycosylated sterols in tomato plant and fruit development, we generated transgenic lines of tomato cultivar Micro-Tom expressing two different amiRNAs devised to silence STEROL GLYCOSYLTRANSFERASE 1, the most actively expressed of the four genes encoding sterol glycosyltransferases in this plant. STEROL GLYCOSYLTRANSFERASE 1 gene silencing caused moderate plant dwarfism and reduced fruit size. Analysis of the profile of glycosylated sterols throughout fruit development demonstrated that the maintenance of proper levels of these compounds during the early stages of fruit development is essential for normal fruit growth, since reduced levels of glycosylated sterols trigger a transcriptional downregulatory response that affects genes involved in processes that are critical for proper fruit development, such as seed filling, cell wall extension and auxin signaling.

Greater Sunlight Exposure during Early Fruit Development Increases Polyphenol Concentration, Soluble Solid Concentration, and Fruit Mass of Cider Apples

The environmental factors that influence cider apple fruit quality, particularly bitter and astringent polyphenols, are not well understood. Five experiments were conducted to investigate how sunlight affects fruit and juice quality. In three studies, shade cloth was placed over entire trees or individual branches at different phenological stages, durations, and opacities. Influence of canopy microclimate was investigated by harvesting fruit from different sections of the tree canopy. In a final study, opaque paper bags were placed over fruit three weeks after full bloom (WAFB) until harvest. Polyphenol concentrations increased rapidly during the first five WAFB and were diluted as fruit grew larger. At harvest, fruit from unshaded trees had 32% greater total polyphenol concentrations and were 11% larger than trees shaded 1–5 WAFB. Shading branches later in the growing season reduced yield but had a modest and inconsistent reduction on polyphenol concentrations. Juice from fruit harvested from the top of the tree canopy had 33% greater polyphenol concentrations and 14% greater soluble solid concentrations than juice from the interior of the canopy. Bagging fruit had inconsistent impacts on polyphenol concentrations. We hypothesize that there is a source sink relationship between carbohydrate availability and polyphenol synthesis in apple fruit during the early stages of fruit development when most polyphenols are produced. Additionally, greater carbohydrate availability in canopies with greater sunlight exposure resulted in larger fruit and improved juice quality from a cider making perspective.

A comprehensive analysis of carotenoids metabolism in two red-fleshed mutants of Navel and Valencia sweet oranges (Citrus sinensis).

Kirkwood Navel and Ruby Valencia are two spontaneous bud mutations of the respective parental lines of sweet orange (Citrus sinensis) Palmer Navel and Olinda Valencia, showing an atypical red pigmentation of the pulp. These red-fleshed varieties are commercially available and highly attractive for consumers but their carotenoid metabolism and the basis of the mutation have not been investigated. The red colour of Kirkwood and Ruby pulp was observed from the very early stages of fruit development until full maturity and associated with an altered carotenoid profiling. The red-fleshed varieties accumulated from 6- up to 1000-times more total carotenoids compared to the standard oranges. Specifically, the pulp of Kirkwood and Ruby accumulated large amounts of phytoene and phytofluene, and moderate contents of lycopene. Moreover, the red-fleshed oranges contained other unusual carotenes as δ-carotene, and lower concentrations of downstream products such as β,β-xanthophylls, abscisic acid (ABA) and ABA-glucosyl ester. This peculiar profile was associated with chromoplasts with lycopene crystalloid structures and round vesicles likely containing colourless carotenes. The flavedo and leaves of Kirkwood and Ruby showed minor changes in carotenoids, mainly limited to higher levels of phytoene. The carotenoid composition in Kirkwood and Ruby fruits was not explained by differences in the transcriptional profile of 26 genes related to carotenoid metabolism, covering the main steps of biosynthesis, catabolism and other processes related to carotenoid accumulation. Moreover, sequence analysis of the lycopene cyclase genes revealed no alterations in those of the red-fleshed oranges compared to the genes of the standard varieties. A striking event observed in Kirkwood and Ruby trees was the reddish coloration of the inner side of the bark tissue, with larger amounts of phytoene, accumulation of lycopene and lower ABA content. These observation lead to the conclusion that the mutation is not only manifested in fruit, affecting other carotenogenic tissues of the mutant plants, but with different consequences in the carotenoid profile. Overall, the carotenoid composition in the red-fleshed mutants suggests a partial blockage of the lycopene β-cyclization in the carotenoid pathway, rendering a high accumulation of carotenes upstream lycopene and a reduced flow to downstream xanthophylls and ABA.

Investigations of the Chemical Composition and Aromatic Properties of Peel Essential Oils throughout the Complete Phase of Fruit Development for Two Cultivars of Sweet Orange (Citrus sinensis (L.) Osb.).

The peel essential oil (PEO) of sweet orange is used for flavoring liquors or foods and in the perfumery and cosmetics industry. The fruit maturity stage can modify the essential oil composition and aromatic properties, but little information is available on the evolution of PEO during the entire time set of fruit development. In this study, the yield, chemical composition and aromatic profile over the three phases of orange development were monitored. Four fruit traits (peel color, weight, acidity and sweetness) were recorded to characterize fruit development. Fruits of two sweet orange cultivars were sampled every two weeks from June to May of the next year. PEO was obtained by hydrodistillation and analyzed by gas chromatography coupled with a flame ionization detector (GC-FID). Compounds were identified with GC coupled with mass spectrometry (GC/MS). Ten expert panelists using the descriptor intensity method described the aromatic profile of PEO samples. The PEO composition was richer in oxygenated compounds at early fruit development stages, with an aromatic profile presenting greener notes. During fruit growth (Phases I and II), limonene’s proportion increased considerably as a few aliphatic aldehydes brought the characteristic of orange aroma. During fruit maturation (from November to March), the PEO composition and aromatic profile were relatively stable. Later, some modifications were observed. Regardless of the fruit development stage, the two sweet oranges presented distinct PEO compositions and aromatic profiles. These results constitute a temporal reference for the chemical and aromatic evolution of sweet orange PEO in the fruit development process under Mediterranean conditions. During the first two phases of fruit development, many changes occur in the PEO composition and aroma, suggesting that their exploitation could create new products.