Fruit Abscission Research Articles

Morphological and genetic characterization of the muscadine fruit abscission zone.

Muscadines face limitations to fresh market production due to high manual labor costs. Mechanical harvesting holds promise for reducing the costs associated with muscadine production but requires cultivars with easily detached fruit at maturity. This study aimed to determine muscadine fruit and pedicel characteristics influencing fruit detachment force (FDF) and to unravel the genes, hormones, and regulatory networks governing muscadine abscission. We characterized the FDF of muscadine fruit across 18 genotypes and at four developmental stages. Following this, we performed a transcriptome analysis using the mature pedicel tissue of two genotypes, a genotype with high FDF at maturity and a genotype with low FDF at maturity, to identify differentially expressed and uniquely expressed genes contributing to fruit detachment. We found that pedicel length, pedicel-fruit junction area, and fruit diameter positively correlated with FDF. This study also identified novel candidate genes, transcription factor families, and pathways associated with muscadine fruit abscission. These findings provide valuable knowledge on the progression of fruit abscission and insights for reducing FDF, particularly in developing machine-harvestable muscadine cultivars and fostering sustainability and efficiency in muscadine production.

LcMPK3 and LcMPK6 positively regulate fruitlet abscission in litchi

Mitogen-activated protein kinase (MAPK) cascades have been discovered to play a fundamental role in regulating organ abscission. However, the identity of protein substrates targeted by MAPK cascades, as well as whether the role of MAPK protein cascades in the abscission process is conserved across different plant species, remain unknown. Here, the role of homologs of MPK3 and MPK6 in regulating fruit abscission were characterized in litchi. Ectopic expression of LcMPK3 or LcMPK6 in Arabidopsis mpk3 mpk6 mutant rescued the deficiency in floral organ abscission, while silencing of LcMPK3 or LcMPK6 in litchi significantly decreased fruitlet abscission. Importantly, a total of 49 proteins interacting with LcMPK3 were identified through yeast two-hybrid screening, including two components of the MAPK signaling cascade, five transcription factors, and two aquaporins. Furthermore, the interaction between LcMPK3/6 with LcBZR1/2, core components in brassinosteroids signaling that suppress litchi fruitlet abscission, was confirmed using in vitro and in vivo assays. Moreover, phos-tag assays demonstrated that LcMPK3/6 could phosphorylate LcBZR1/2, with several phosphorylation residues identified. Together, our findings suggest that LcMPK3 and LcMPK6 play a positive regulatory role in fruitlet abscission in litchi, and offer crucial information for the investigation of mechanisms underlying MPK3/6-mediated organ abscission in plants.

Engineering the future of Physalis grisea: A focus on agricultural challenges, model species status, and applied improvements

Societal Impact StatementGroundcherry (Physalis grisea) is a plant species grown for its flavorful fruit. The fruit drops from the plant, hence the common name groundcherry. This makes harvest cumbersome and puts the fruit at risk for carrying soil‐borne pathogens, therefore making them unsellable. Furthermore, insects often damage the plants, reducing yield. Advances in gene editing offer promise for addressing these issues and aiding home gardeners and farmers. Improvement will expand access to this nutritious fruit, rich in potassium, vitamin C, and antioxidants. Additionally, studies of its biology could serve as a model for improving other fruiting plants, particularly underutilized species.SummaryP. grisea is an underutilized, semidomesticated fruit crop with rising agronomic value. Several resources have been developed for its use in fundamental biological research, including a plant transformation system and a high‐quality reference genome. Already, P. grisea has been used as a model to investigate biological phenomena including inflated calyx syndrome and gene compensation. P. grisea has also been used to demonstrate the potential of fast‐tracking domestication trait improvement through approaches such as CRISPR/Cas9 gene editing. This work has led to the Physalis Improvement Project, which relies on reverse genetics to understand the mechanisms that underlie fruit abscission and plant–herbivore interactions to guide approaches for improvement of undesirable characteristics. CRISPR/Cas9 gene editing has been used to target P. grisea genes that are suspected to act in fruit abscission, particularly orthologs of those that are reported in tomato abscission zone development. A similar approach is being taken to target P. grisea genes involved in the withanolide biosynthetic pathway to determine the impact of withanolides on plant–herbivore interactions. Results from these research projects will lead to a greater understanding of important biological processes and will also generate knowledge needed to develop cultivars with reduced fruit drop and increased resistance to insect herbivory.

An ethylene response factor AcERF116 identified from A. catechu is involved in fruitlet abscission

Procedural abscission of outer reproductive organs during flower and fruit development occurs in most plant lineages. Undesired abscission, such as fruitlet shedding causes considerable yield loss in many fruit-producing species. Ethylene is one of the key factors regulating organ abscission. However, the participants involved in the ethylene-mediated abscission pathway remains largely unidentified. In this study, we focused on the ethylene response transcription factors (ERFs) regulating fruitlet abscission in an industrial tree species, A. catechu. A total of 165 ERF genes have been found in the A. catechu genome and eight of these showed distinct expression between the “about-to-abscise” and “non-abscised” samples. An AcERF116 gene with high expression level in the fruit abscission zone (FAZ) was selected for further study. Overexpression of the AcERF116 gene accelerated cell separation in the abscission zone (AZ) and promoted pedicel abscission in transgenic tomato lines. The PG (ploygalacturonase) activity was enhanced in the FAZs of A. catechu fruitlets during ethylene-induced fruitlet abscission, while the PME (pectin methylesterase) activity was suppressed. In addition, cytosolic alkalization was observed in the AZs during abscission in both tomato and A. catechu. Our results suggest that AcERF116 plays a critical role in the crosstalk of ethylene and fruitlet abscission in A. catechu.

First Report of Colletotrichum siamense Causing Fruit Anthracnose on Pomegranate (Punica granatum) in China.

As a native crop in central Asia, pomegranate (Punica granatum L.) has been cultivated in China for more than 2000 years (Yuan et al. 2007). In August 2022, typical symptoms of anthracnose were observed on pomegranate fruitlets in the main cultivation area (34°22'36″N, 109°15'58″E) in Shaanxi Province, China. The disease incidence was approximately 10 to 15% in the field. The initial symptoms were slightly small, light, dark, sunken lesions with irregular, circular shapes. As the disease progressed, the necrotic lesions gradually expanded and merged, eventually leading to the abscission of fruits (Figure 1, A). The symptomatic lesion samples of the pomegranate were sterilized for 1.5 min in 75% ethanol and 2 min in 1% NaClO and rinsed for 2 min in sterile water three times. The sterilized samples were dried on sterile filter paper and placed on potato dextrose agar (PDA) media at 25 ℃ for 5 days. The mycelia of the isolate were white, cottony, and diffuse (Figure 1, B and C). The conidia were single-celled, smooth, aseptate, and cylindrical with slightly rounded ends, measured 13.5 to 17.5 μm long and 3.5 to 6.5 μm wide (mean 16.0 × 4.5 μm, n = 50) (Figure 1, D). These morphological characteristics were identical to those of Colletotrichum siamense (Weir et al. 2012; Cannon et al. 2012; Zhuo et al. 2022). For accurate molecular characterization of the fungus, genomic DNA was extracted from the hyphae of the two isolates using microorganism lysis buffer (Takara, Japan). The internal transcribed spacer (ITS), calmodulin (CAL), actin (ACT), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and beta-tubulin (TUB2) regions were amplified and sequenced. All the sequences were submitted to GenBank with accession numbers OQ832556 (ITS), OQ848589 (GAPDH), OQ848590 (ACT), OQ848591 (CAL), and OQ986593 (TUB2). The isolates showed 99 to 100% identity with sequences of Colletotrichum siamense (100% with GAPDH, ACT, CAL, and TUB2; 99.81% with ITS). The morphology of the strain was studied, and multilocus (ITS, GAPDH, ACT, CAL, and TUB2) phylogenetic analysis was performed (Figure 2). Therefore, the causal pathogen was identified as C. siamense based on the results of morphological and molecular analyses. Pathogenicity assays were performed on pomegranate (cv. Lishanhong) fruits. A conidial suspension (1×106 conidia/mL) was sprayed onto 10 unwounded fruits to inoculate them as infected samples, and the controls were inoculated with a sterile water suspension. All the samples were maintained in an artificial climate box at 25 ± 2 ℃ with 70% relative humidity, and the photoperiod was set as 12:12 light:dark. After 5 to 7 days, anthracnose symptoms developed on the surface of the inoculated fruit, whereas the control fruits remained healthy. The diseased fruits exhibited brown necrotic lesions, whereas the upper surfaces of the control fruits remained asymptomatic. The morphological and molecular characteristics of the reisolated pathogen were identical to those of the original fungus isolated from the natural fruit. C. siamense has been reported to cause anthracnose in the southeastern United States (Xavier et al. 2019). The pathogen causing anthracnose on pomegranates has been reported to be Colletotrichum fructicola in China (Hu et al. 2023). To our knowledge, this is the first report of anthracnose on pomegranate fruits caused by C. siamense in China. This disease can directly affect the quality and yield of the fruit. Thus, information about the characteristics of this disease could provide a theoretical basis for its prevention and control.

SlBEL11 regulates flavonoid biosynthesis, thus fine-tuning auxin efflux to prevent premature fruit drop in tomato.

Auxin regulates flower and fruit abscission, but how developmental signals mediate auxin transport in abscission remains unclear. Here, we reveal the role of the transcription factor BEL1-LIKE HOMEODOMAIN11 (SlBEL11) in regulating auxin transport during abscission in tomato (Solanum lycopersicum). SlBEL11 is highly expressed in the fruit abscission zone, and its expression increases during fruit development. Knockdown of SlBEL11 expression by RNA interference (RNAi) caused premature fruit drop at the breaker (Br) and 3 d post-breaker (Br+3) stages of fruit development. Transcriptome and metabolome analysis of SlBEL11-RNAi lines revealed impaired flavonoid biosynthesis and decreased levels of most flavonoids, especially quercetin, which functions as an auxin transport inhibitor. This suggested that SlBEL11 prevents premature fruit abscission by modulating auxin efflux from fruits, which is crucial for the formation of an auxin response gradient. Indeed, quercetin treatment suppressed premature fruit drop in SlBEL11-RNAi plants. DNA affinity purification sequencing (DAP-seq) analysis indicated that SlBEL11 induced expression of the transcription factor gene SlMYB111 by directly binding to its promoter. Chromatin immunoprecipitation-quantitative polymerase chain reaction and electrophoretic mobility shift assay showed that S. lycopersicum MYELOBLASTOSIS VIRAL ONCOGENE HOMOLOG111 (SlMYB111) induces the expression of the core flavonoid biosynthesis genes SlCHS1, SlCHI, SlF3H, and SlFLS by directly binding to their promoters. Our findings suggest that the SlBEL11-SlMYB111 module modulates flavonoid biosynthesis to fine-tune auxin efflux from fruits and thus maintain an auxin response gradient in the pedicel, thereby preventing premature fruit drop.

Enhancing productivity, modifying biochemical parameters, and regulating the phenylpropanoid pathway in 'Le-Conte' pears through optimal protocatechuic acid treatments

BackgroundThis study aimed to investigate the impact of protocatechuic acid (PRC) treatments on the productivity and fruit quality of 'Le-Conte' pears, with a specific focus on productivity, stone cells content, and antioxidant activity. The research spanned over three consecutive cultivating seasons, with the first season serving as a preliminary study to determine the optimal PRC concentrations and the most effective number of spray applications. During the initial season, response surface methodology (RSM) was employed to optimize PRC concentration and application frequency. PRC was evaluated at concentrations ranging from 50 to 400 ppm, with treatment frequencies of either once or twice. Considering the optimal conditions obtained from RSM results, PRC treatments at 200 ppm and 300 ppm were applied twice, and their respective effects were studied in comparison to the control in the following seasons.ResultsRSM results indicated that PRC at 200 and 300 ppm, applied twice, once during full bloom and again three weeks later, yielded the most significant effects. Subsequent studies revealed that PRC treatments had a substantial impact on various aspects of fruit production and quality. Applying 300 ppm PRC once during full bloom and again three weeks later resulted in higher fruit set percentages, lower fruit abscission, and enhanced fruit yield compared to untreated trees. Additionally, the 200 ppm PRC treatment maintained physicochemical characteristics such as fruit color, increased total soluble solids (TSS), and total sugar, and maintained higher ascorbic acid content and antioxidant capacity in the fruits while reducing stone cells content and lignin. Notably, enzyme activities related to phenylpropanoid metabolism and stone cells, including phenylalanine ammonia-lyase (PAL), cinnamate-4-hydroxylase (C4H), 4-Coumarate-CoA Ligase (4CL), cinnamyl alcohol dehydrogenase (CAD), and cinnamoyl-CoA reductase (CCR), as well as peroxidase, polyphenol oxidase, and laccase, were significantly regulated by PRC treatments.ConclusionOverall, this study suggests that PRC treatments are suitable for enhancing pear yield and quality, with PRC at 200 ppm being the more recommended option over 300 ppm. This approach serves as an effective strategy for achieving a balance between enhancing the productivity and fruit quality of 'Le-Conte' pears.

Transcriptome analysis unravels key pathways and hub genes related to immature fruit abscission in Camellia oleifera.

Immature fruit abscission of Camellia oleifera (C. oleifera) is a common problem limiting yield increases. However, the regulatory mechanisms underlying immature fruit abscission in C. oleifera are unclear. In this study, we systematically investigated changes in the morphological, physiological, and gene expression of fruit abscission zones (FAZs) of soon-to-abscise fruits (M2). We found that fruit abscission before ripening mainly occurs during the August abscission stage of 'Huashuo'. At the beginning of this stage, the FAZs of M2 have a marked dent, and the separation layer structures are preliminarily formed. Phytohormone analysis showed that the contents of indole-3-acetic acid (IAA) and jasmonic acid (JA) in the FAZs of M2 were significantly decreased compared with the non-abscised fruits, while the content of trans-zeatin (TZR) was increased. Transcriptome analysis identified differentially expressed genes (DEGs) mainly involved in phytohormone metabolism, including ethylene, auxin, JA, and the cis-zeatin signal transduction pathway. There were also many DEGs involved in cell wall catabolism. Weighted gene co-expression network analysis (WGCNA) further suggested that the transcription factors NAC100 and ERF114 participate in the immature fruit abscission of C. oleifera. This study provides insights into the fruit abscission mechanism of C. oleifera.

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.

Effects of Ethrel and auxin applications on date palm fruit abscission during development

'Medjoul' is a large semidry date cultivar that is marketed as a special elite product. Fruit size and quality are determined by fruit load, which is dependent on the level of fruit set, fruitlet thinning protocols and natural drop. Currently there is no information on the process of natural fruit abscission in date palms and specifically not on abscission of 'Medjoul'. In the present study abscission levels were characterized through fruit development in vivo and in vitro. Fruit abscise throughout development. During two stages, at an 'Early fruitlet drop' and a 'June drop' (at 25–45 and 80–100 days after pollination respectively), specifically high rates of abscission were observed. The level of fruit set and the fruit load affects these two peaks respectively. Ethrel treatment, an ethylene releasing chemical, significantly induced fruitlet drop while Auxin (2,4-D) treatment reduced the rate of natural fruit drop in vitro, especially during the developmental stages with high natural abscission. A specific abscission zone located at the base of the fruit, just between the calyx and spikelet was detected. Following Ethrel treatment, breaks and cracks in this tissue were detected. This data will enable better understanding of fruitlet and fruit abscission in date palm, which is extremely important for a high quality production of 'Medjoul' dates.

Studies on crossability in cashew (Anacardium occidentale L.) genotypes

Successful hybridization primarily depends on the crossability of the parents involved as well as development of the F1 hybrids and their derivatives. In the present study, 12 crosses were attempted to study the crossability relationship among cashew genotypes. Among the crosses, the highest crossability was recorded in the cross H-303 x VTH 711/4 (17.16%), whereas, high rate of abscission of young fruits was observed in crosses involving NRCC Selection -2 as female parent. The genotype VTH 711/4 has shown substantially high per cent of crossability and better nut set with different genotypes of cashew.

Response of Abscission Zone of Blue Honeysuckle (Lonicera caerulea L.) Fruit to GA3 and 2,4-D Spray Application

The nutritional value of blue honeysuckle (Lonicera caerulea L.) fruit is abundant; however, its production faces challenges due to a short harvesting period and fruit drop issues. In this study, the effects and potential mechanisms of two different plant growth regulators, GA3 (Gibberellins acid) and 2,4-D (2,4-Dichlorophenoxyacetic acid), on blue honeysuckle fruit abscission and abscission layer formation were investigated. The main cultivated variety of blue honeysuckle, ‘Berel’, was used as the experimental material. GA3 and 2,4-D were sprayed on the plants from the veraison. The anatomical structure of the fruit abscission zone (FAZ) was observed after treatment. Key enzymes involved in cell wall degradation, pectinase, cellulase, polygalacturonase, and pectin methylesterase, were analyzed for their activities. Furthermore, the gene expression levels of cell wall detachment-related genes CX1, CX2, PL20, PE, and key genes for gibberellin and ethylene synthesis GA2OX1, GA1, ACO, and ACO3 were examined. The results indicated that the application of GA3 and 2,4-D could delay the formation of the abscission layer. In the FAZ treated with GA3 and 2,4-D at 5 DAT, the activity of key enzymes involved in cell wall degradation decreased, the expression of genes related to cell wall degradation enzymes and key genes for ethylene synthesis was inhibited, and the drop of fruit reduced. In conclusion, exogenous application of GA3 and 2,4-D suppresses the abscission of ‘Berel’ blue honeysuckle fruit, likely through the inhibition of cell wall degradation and abscission layer formation.

Phytohormones and candidate genes synergistically regulate fruitlet abscission in Areca catechu L.

BackgroundThe fruit population of most plants is under the control of a process named “physiological drop” to selectively abort some developing fruitlets. However, frequent fruitlet abscission severely restricts the yield of Areca catechu. To reveal the physiological and molecular variations in this process, we detected the variation of phytohormone levels in abscised and non-abscised fruitlets in A. catechu.ResultsThe levels of gibberellin acid, jasmonic acid, salicylic acid, abscisic acid and zeatin were elevated, while the indole-3-acetic acid and indole-3-carboxaldehyde levels were declined in the “about-to-abscise” part (AB) of abscission zone (AZ) compared to the “non-abscised” part (CK). Then the differentially expressed genes (DEGs) between AB and CK were screened based on transcriptome data. DEGs involved in phytohormone synthesis, response and transportation were identified as key genes. Genes related to cell wall biosynthesis, degradation, loosening and modification, and critical processes during fruit abscission were identified as role players. In addition, genes encoding transcription factors, such as NAC, ERF, WRKY, MADS and Zinc Finger proteins, showed differentially expressed patterns between AB and CK, were also identified as candidates.ConclusionsThese results unraveled a phytohormone signaling cross talk and key genes involved in the fruitlet abscission process in A. catechu. This study not only provides a theoretical basis for fruitlet abscission in A. catechu, but also identified many candidate genes or potential molecular markers for further breeding of fruit trees.

Impact of 24-epibrassinoliode and methyl jasmonate on quality of Red Delicious apples.

Changes in apple fruit quality indices in response to foliar spray with 24-epibrassinolide (EBL) at 0 and 1 μmol L-1 and methyl jasmonate (MeJA) at 0 and 0.5 μmol L-1 , as well as the combination of these phytohormones, were investigated at harvest and during cold storage. Both phytohormones synergistically enhanced the fruit firmness, specific weight, size, fresh weight, water content, total antioxidant activity, total phenolics, ascorbic acid, total anthocyanins, total soluble solids/titratable acidity ratio and precocity. In addition, the fruit abscission pattern was changed in response to different treatments. Treated fruit exhibited lower weight loss and internal breakdown symptoms and higher total soluble solids index, firmness and phytochemicals during cold storage. A negative correlation was seen between fruit mass, firmness, specific weight, antioxidant activity, total phenolics and vitamin C content with internal breakdown occurrence and weight loss. Foliar spray with EBL and MeJA during the growth season is a good environmental friendly and safe method for enhancing the apple fruit different quality parameters, marketability and postharvest life. © 2023 Society of Chemical Industry.

Effect of shading nets on environmental conditions and fruit abscission in quince (Cydonia oblonga L.)

The quince tree has been cultivated since ancient times in the province of Isfahan in Iran. Flower and fruit drop is one of the most important problems in the cultivation of quince in Iran. In this study, the role of shading nets as a protective factor in quince orchard was investigated to adjust climatic factors and reduce flower and fruit drop. A 20-year-old quince orchard was equipped with shading net system, and another part was compared as a control plot without shading net system in 2021 and 2022. The color of shading net and the percentage of shading were 30% green, 50% green and 50% white. According to the results, flowers opened five days later under the shading nets than outdoors. Percent fruit set, leaf length and width, number of fruits, and yield were significantly higher under the shade net than outdoors. Green 30% had the highest chlorophyll fluorescence index. The fruit set percentage and yield inside the shading nets were more than twice that outside. Total soluble solids and the abscission percentage in the control plot were more than the plot under nets. According to meteorological data, the temperature inside the shade netting was only 0.33–0.67 °Celsius lower than outside, but the radiation intensity outside the nets (30,362.44 lx) was more than two and a half times the amount of radiation under the shading nets (11,876.02 Lux). According to the obtained results, it is recommended to use the shade nets in quince orchards, where happened abscission of flowers and fruits leads to a decrease in yield. The green shade net color of 30 and 50% is recommended for orchards due to the higher chlorophyll fluorescence index, fruit set percentage, number of fruits, and yield.

Genetic analysis of heat tolerance in hot pepper: insights from comprehensive phenotyping and QTL mapping.

High temperatures present a formidable challenge to the cultivation of hot pepper, profoundly impacting not only vegetative growth but also leading to flower and fruit abscission, thereby causing a significant reduction in yield. To unravel the intricate genetic mechanisms governing heat tolerance in hot pepper, an F2 population was developed through the crossing of two distinct genotypes exhibiting contrasting heat tolerance characteristics: DLS-161-1 (heat tolerant) and DChBL-240 (heat susceptible). The F2 population, along with the parental lines, was subjected to comprehensive phenotyping encompassing diverse morphological, physiological, and biochemical heat-related traits under high temperature conditions (with maximum temperature ranging from 31 to 46.5°C and minimum temperature from 15.4 to 30.5°C). Leveraging the Illumina Nova Seq-6000 platform, Double digest restriction-site associated DNA sequencing (ddRAD-seq) was employed to generate 67.215 Gb data, with subsequent alignment of 218.93 million processed reads against the reference genome of Capsicum annuum. Subsequent variant calling and ordering resulted in 5806 polymorphic SNP markers grouped into 12 LGs. Further QTL analysis identified 64 QTLs with LOD values ranging from 2.517 to 11.170 and explained phenotypic variance ranging from 4.05 to 19.39%. Among them, 21 QTLs, explaining more than 10% phenotypic variance, were identified as major QTLs controlling 9 morphological, 3 physiological, and 2 biochemical traits. Interestingly, several QTLs governing distinct parameters were found to be colocalized, suggesting either a profound correlation between the QTLs regulating these traits or their significant genomic proximity. In addition to the QTLs, we also identified 368380 SSR loci within the identified QTL regions, dinucleotides being the most abundant type (211,381). These findings provide valuable insights into the genetics of heat tolerance in hot peppers. The identified QTLs and SSR markers offer opportunities to develop heat-tolerant varieties, ensuring better crop performance under high-temperature conditions.

MaABI5 and MaABF1 transcription factors regulate the expression of MaJOINTLESS during fruit abscission in mulberry (Morus alba L.).

Mulberry holds significant economic value. However, during the ripening stage of its fruit, the phenomenon of abscission, resulting in heavy fruit drop, can severely impact the yield. The formation of off-zone structures is a critical factor in the fruit abscission process, and this process is regulated by multiple transcription factors. One such key gene that plays a significant role in the development of the off-zone in the model plant tomato is JOINTLESS, which promotes the expression of abscission-related genes and regulates the differentiation of abscission zone tissue cells. However, there is a lack of information about fruit abscission mechanism in mulberry. Here, we analyzed the MaJOINTLESS promoter and identified the upstream regulators MaABF1 and MaABI5. These two regulators showed binding with MaJOINTLESS promoter MaABF1 (the ABA Binding Factor/ABA-Responsive Element Binding Proteins) activated the expression of MaJOINTLESS, while MaABI5 (ABSCISIC ACID-INSENSITIVE 5) inhibited the expression of MaJOINTLESS. Finally, the differentially expressed genes (DEGs) were analyzed by transcriptome sequencing to investigate the expression and synergistic relationship of endogenous genes in mulberry during abscission. GO classification and KEGG pathway enrichment analysis showed that most of the DEGs were concentrated in MAPK signaling pathway, flavonoid biosynthesis, citric acid cycle, phytohormone signaling, amino acid biosynthesis, and glycolysis. These results provide a theoretical basis for subsequent in-depth study of physiological fruit abscission in mulberry.

Genome-wide identification of GH9 gene family and the assessment of its role during fruit abscission zone formation in Vaccinium ashei.

The genomic location and stage-specific expression pattern of GH9 genes reveal their critical roles during fruit abscission zone formation in Vaccinium ashei. Glycosyl hydrolase family 9 (GH9) cellulases play a crucial role in both cellulose synthesis and hydrolysis during plant growth and development. Despite this importance, there is currently no study on the involvement of GH9-encoding genes, specifically VaGH9s, in abscission zone formation of rabbiteye blueberries (Vaccinium ashei). In this study, we identified a total of 61 VaGH9s in the genome, which can be classified into 3 subclasses based on conserved motifs and domains, gene structures, and phylogenetic analyses. Our synteny analysis revealed that VaGH9s are more closely related to the GH9s of Populus L. than to those of Arabidopsis, Vitis vinifera, and Citrus sinensis. In silico structural analysis predicted that most of VaGH9s are hydrophilic, and localized in cell membrane and/or cell wall, and the variable sets of cis-acting regulatory elements and functional diversity with four categories of stress response, hormone regulation, growth and development, and transcription factor-related elements are present in the promoter sequence of VaGH9s genes. Transcriptomic analysis showed that there were 22 differentially expressed VaGH9s in fruit abscission zone tissue at the veraison stage, and the expression of VaGH9B2 and VaGH9C10 was continuously increased during fruit maturation, which were in parallel with the increasing levels of cellulase activity and oxidative stress indicators, suggesting that they are involved in the separation stage of fruit abscission in Vaccinium ashei. Our work identified 22 VaGH9s potentially involved in different stages of fruit abscission and would aid further investigation into the molecular regulation of abscission in rabbiteye blueberries fruit.

Regulation of climacteric fruit ripening in melon, recent advances and future challenges.

Fruit ripening is a complex and highly regulated process where tomato and strawberry have been the model species classically used for studying climacteric and non-climacteric fleshy fruit ripening types, respectively. Melon has emerged as an alternative ripening model because climacteric and non-climacteric cultivars exist, which makes it possible to dissect the regulation of ripening using a genetic approach. Several QTLs that regulate climacteric fruit ripening have been identified to date, and their combination in both climacteric and non-climacteric genetic backgrounds resulted in lines with different ripening behaviors, demonstrating that the climacteric intensity can be genetically modulated. The review discusses our current knowledge of the physiological changes observed during melon climacteric fruit ripening as ethylene production, fruit abscission, chlorophyll degradation, firmness and aroma, as well as their complex genetic control. From pioneer experiments in which ethylene biosynthesis was silenced, to the recent genetic edition of ripening regulators, current data suggest that the climacteric response is determined by the interaction of several loci under quantitative inheritance. The exploitation of the rich genetic diversity of melon will enable the discovery of additional genes involved in the regulation of the climacteric response, ultimately leading to breeding aromatic melon fruits with extended shelf life.

Transcriptomic and metabolomic analyses reveal molecular mechanisms associated with the natural abscission of blue honeysuckle (Lonicera caerulea L.) ripe fruits

Blue honeysuckle (Lonicera caerulea L.) is rich in phenolic compounds and has an extremely high nutritional value. Fruit abscission in the ripe period significantly impacts production and economic benefits. However, the mechanism associated with the abscission of blue honeysuckle fruit remains largely unknown. The easy-abscission cultivar ‘HSY’ and the hard-abscission cultivar ‘Berel’ were selected as plant materials. Anatomical changes of the ‘HSY’ fruit abscission zone (FAZ) during the abscission mainly included cell expansion, detachment, and collapse. Active changes in cell wall-degrading enzyme activity between 39 days postanthesis (DPA) and 55 DPA in ‘HSY’ FAZ, but not in ‘Berel’, suggest a critical role for cell-wall-degrading enzymes in regulating abscission. Transcriptome and metabolome analyses revealed that the genes and metabolites responding to abscission mainly act on pathways such as plant hormone signal transduction, starch and sucrose metabolism, pentose and glucuronate interconversions, and phenylpropanoid biosynthesis. The regulatory pathways of fruit abscission are mainly summarized into two parts: phytohormone synthesis and signal transduction, FAZ cell wall metabolism. In this study, 46 key genes related to plant hormone response, 45 key genes involved in FAZ cell wall metabolism, and 73 transcription factors were screened. Quantitative real-time PCR (qRT-PCR) assessed the expression pattern of 12 selected candidate genes, demonstrating the accuracy of the transcriptome data and elucidating the expression patterns of key candidate genes during growth and development. This study will provide an essential resource for understanding the molecular regulatory mechanism of fruit abscission in the blue honeysuckle.