Abscission Research Articles

The transcriptional control of LcIDL1-LcHSL2 complex by LcARF5 integrates auxin and ethylene signaling for litchi fruitlet abscission.

At the physiological level, the interplay between auxin and ethylene has long been recognized as crucial for the regulation of organ abscission in plants. However, the underlying molecular mechanisms remain unknown. Here, we identified transcription factors involved in indoleacetic acid (IAA) and ethylene (ET) signaling that directly regulate the expression of INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) and its receptor HAESA (HAE), which are key components initiating abscission. Specifically, litchi IDA-like 1 (LcIDL1) interacts with the receptor HAESA-like 2 (LcHSL2). Through in vitro and in vivo experiments, we determined that the auxin response factor LcARF5 directly binds and activates both LcIDL1 and LcHSL2. Furthermore, we found that the ETHYLENE INSENSITIVE 3-like transcription factor LcEIL3 directly binds and activates LcIDL1. The expression of IDA and HSL2 homologs was enhanced in LcARF5 and LcEIL3 transgenic Arabidopsis plants, but reduced in ein3 eil1 mutants. Consistently, the expressions of LcIDL1 and LcHSL2 were significantly decreased in LcARF5- and LcEIL3-silenced fruitlet abscission zones (FAZ), which correlated with a lower rate of fruitlet abscission. Depletion of auxin led to an increase in 1-aminocyclopropane-1-carboxylic acid (the precursor of ethylene) levels in the litchi FAZ, followed by abscission activation. Throughout this process, LcARF5 and LcEIL3 were induced in the FAZ. Collectively, our findings suggest that the molecular interactions between litchi AUXIN RESPONSE FACTOR 5 (LcARF5)-LcIDL1/LcHSL2 and LcEIL3-LcIDL1 signaling modules play a role in regulating fruitlet abscission in litchi and provide a long-sought mechanistic explanation for how the interplay between auxin and ethylene is translated into the molecular events that initiate abscission.

Integrated analysis of the transcriptome and metabolome reveals the molecular mechanism regulating cotton boll abscission under low light intensity

BackgroundCotton boll shedding is one of the main factors adversely affecting the cotton yield. During the cotton plant growth period, low light conditions can cause cotton bolls to fall off prematurely. In this study, we clarified the regulatory effects of low light intensity on cotton boll abscission by comprehensively analyzing the transcriptome and metabolome.ResultsWhen the fruiting branch leaves were shaded after pollination, all of the cotton bolls fell off within 5 days. Additionally, H2O2 accumulated during the formation of the abscission zone. Moreover, 10,172 differentially expressed genes (DEGs) and 81 differentially accumulated metabolites (DAMs) were identified. A KEGG pathway enrichment analysis revealed that the identified DEGs and DAMs were associated with plant hormone signal transduction and flavonoid biosynthesis pathways. The results of the transcriptome analysis suggested that the expression of ethylene (ETH) and abscisic acid (ABA) signaling-related genes was induced, which was in contrast to the decrease in the expression of most of the IAA signaling-related genes. A combined transcriptomics and metabolomics analysis revealed that flavonoids may help regulate plant organ abscission. A weighted gene co-expression network analysis detected two gene modules significantly related to abscission. The genes in these modules were mainly related to exosome, flavonoid biosynthesis, ubiquitin-mediated proteolysis, plant hormone signal transduction, photosynthesis, and cytoskeleton proteins. Furthermore, TIP1;1, UGT71C4, KMD3, TRFL6, REV, and FRA1 were identified as the hub genes in these two modules.ConclusionsIn this study, we elucidated the mechanisms underlying cotton boll abscission induced by shading on the basis of comprehensive transcriptomics and metabolomics analyses of the boll abscission process. The study findings have clarified the molecular basis of cotton boll abscission under low light intensity, and suggested that H2O2, phytohormone, and flavonoid have the potential to affect the shedding process of cotton bolls under low light stress.

Comparative analysis of exogenously applied synthetic auxins and micronutrients for effective management of fruit drop and quality improvement in subtropical Japanese plum (Prunus salicina Lindl.)

Foliar application of plant growth regulators and micronutrients is a rapid uptake strategy of plant-feeding directly through leaves irrespective of soil condition. This experiment was conducted to assess the impact of the foliar application of synthetic auxins and micronutrients on subtropical Japanese plum (Prunus salicina Lindl.) fruit yield and quality. The experiment was performed in a plum orchard based on a completely randomized block design with nine treatments and three replications. The foliar treatments included NAA 15 ppm, NAA 15 ppm + urea 2%, 2,4-D 10 ppm, 2,4-D 10 ppm + urea 2%, borax 0.50%, borax 0.50% + urea 2%, ZnSO4 0.50%, ZnSO4 0.50% + urea 2%, and control (sprayed with distilled water) applied as a two spray in 15 days interval after fruit set. Foliar application of NAA 15 ppm + urea 2% led to least fruit drop followed by highest fruit yield. The fruit physicochemical attributes including fruit length and diameter, fruit weight, pulp weight, total soluble solids, titratable acidity, sugars, and ascorbic acid were also significantly improved by foliar spray of NAA 15 ppm + urea 2%. However, all the treatments were ineffective in improving anthocyanin and total phenol content of ‘Satluj Purple’ plum. The results further revealed that reduced fruit drop followed by highest fruit yield with foliar application of NAA 15 ppm + urea 2% was associated with reduced activity of cell wall degrading enzymes viz., cellulase and polygalacturonase at abscission zone.

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.

Dissection of the IDA promoter identifies WRKY transcription factors as abscission regulators in Arabidopsis.

Plants shed organs such as leaves, petals, or fruits through the process of abscission. Monitoring cues such as age, resource availability, and biotic and abiotic stresses allow plants to abscise organs in a timely manner. How these signals are integrated into the molecular pathways that drive abscission is largely unknown. The INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) gene is one of the main drivers of floral organ abscission in Arabidopsis and is known to transcriptionally respond to most abscission-regulating cues. By interrogating the IDA promoter in silico and in vitro, we identified transcription factors that could potentially modulate IDA expression. We probed the importance of ERF- and WRKY-binding sites for IDA expression during floral organ abscission, with WRKYs being of special relevance to mediate IDA up-regulation in response to biotic stress in tissues destined for separation. We further characterized WRKY57 as a positive regulator of IDA and IDA-like gene expression in abscission zones. Our findings highlight the promise of promoter element-targeted approaches to modulate the responsiveness of the IDA signaling pathway to harness controlled abscission timing for improved crop productivity.

Exploration of a multifunctional biocontrol agent Streptomyces sp. JCK-8055 for the management of apple fire blight.

Apple fire blight, caused by the bacterium Erwinia amylovora, is a devastating disease of apple and pear trees. Biological control methods have attracted much attention from researchers to manage plant diseases as they are eco-friendly and viable alternatives to synthetic pesticides. Herein, we isolated Streptomyces sp. JCK-8055 from the root of pepper and investigated its mechanisms of action against E. amylovora. Streptomyces sp. JCK-8055 produced aureothricin and thiolutin, which antagonistically affect E. amylovora. JCK-8055 and its two active metabolites have a broad-spectrum in vitro activity against various phytopathogenic bacteria and fungi. They also effectively suppressed tomato bacterial wilt and apple fire blight in in vivo experiments. Interestingly, JCK-8055 colonizes roots as a tomato seed coating and induces apple leaf shedding at the abscission zone, ultimately halting the growth of pathogenic bacteria. Additionally, JCK-8055 can produce the plant growth regulation hormone indole-3-acetic acid (IAA) and hydrolytic enzymes, including protease, gelatinase, and cellulase. JCK-8055 treatment also triggered the expression of salicylate (SA) and jasmonate (JA) signaling pathway marker genes, such as PR1, PR2, and PR3. Overall, our findings demonstrate that Streptomyces sp. JCK-8055 can control a wide range of plant diseases, particularly apple fire blight, through a combination of mechanisms such as antibiosis and induced resistance, highlighting its excellent potential as a biocontrol agent. KEY POINTS: • JCK-8055 produces the systemic antimicrobial metabolites, aureothricin, and thiolutin. • JCK-8055 treatment upregulates PR gene expression in apple plants against E. amylovora. • JCK-8055 controls plant diseases with antibiotics and induced resistance.

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.

Transcriptome differential expression analysis of defoliation in different lemon varieties under drought treatment.

'Allen Eureka' is a bud variety of Eureka lemon with excellent fruiting traits, but severe winter defoliation affects the following year's yield, and the response mechanism of lemon defoliation is currently unknown. Two lemon cultivars ('Allen Eureka' and 'Yunning No. 1') with different defoliation traits were used as materials to investigate the molecular regulatory mechanisms of different leaf abscission periods in lemons. The petiole abscission zone was collected at three different defoliation stages, namely, the predefoliation stage (k15), the middefoliation stage (k30), and the postdefoliation stage (k45). Transcriptome sequencing was performed to analyze the gene expression differences between these two cultivars. A total of 1141, 2695, and 1433 differentially expressed genes (DEGs) were obtained in k15, k30, and k45, respectively, and the number of DEGs in k30 was the largest. GO analysis revealed that the DEGs between the two cultivars were mainly enriched in processes related to hydrolase activity, chitinase activity, oxidoreductase activity, and transcription regulator activity in the defoliation stages. KEGG analysis showed that the DEGs were concentrated in k30, which involved plant hormone signal transduction, phenylpropanoid biosynthesis, and biosynthesis of amino acids. The expression trends of some DEGs suggested their roles in regulating defoliation in Lemon. Seven genes were obtained by WGCNA, including sorbitol dehydrogenase (CL9G068822012_alt, CL9G068820012_alt, CL9G068818012_alt), abscisic acid 8'-hydroxylase (CL8G064053012_alt, CL8G064054012_alt), and asparagine synthetase (CL8G065162012_alt, CL8G065151012_alt), suggesting that these genes may be involved in the regulation of lemon leaf abscission.

Analysis of Nitrogen Dynamics and Transcriptomic Activity Revealed a Pivotal Role of Some Amino Acid Transporters in Nitrogen Remobilization in Poplar Senescing Leaves.

Leaf senescence is an important developmental process for deciduous trees during which part of leaf nitrogen is remobilized to branches, thus being beneficial for nitrogen conservation. However, the associated regulatory mechanism remains largely unknown in deciduous trees. In this study, nitrogen dynamics and transcriptomic activity in senescing leaves were measured during autumnal senescence in hybrid poplar. Both concentrations of leaf total nitrogen (N) and amine compounds were found to decline from the pre-senescence (PRE) to the middle-senescence (MS) stage. Although the total N concentration decreased further from MS to the late-senescence (LS) and leveled off to abscission (ABS) stage, amine compound concentration increased continuously from MS to ABS, suggesting that translocation of amine compounds underperformed production of amine compounds in leaves during this period. L-glutamate, L-glutamine and α-aminoadipic acid were the top three amine compounds accumulated in senescent leaves. RNA-Seq profiling identified thousands of differentially expressed genes (DEGs) with functional association with a metabolic transition towards disassimilation. Many genes encoding amino acid metabolism enzymes and amino acid transporters (AATs) were up-regulated. Comparison of expression trend with leaf N dynamics and phylogenetic analysis identified several PtAATs which exhibited down-regulation from MS to LS stage and putatively limited leaf N remobilization. This study can serve as a primary basis to further elucidate the molecular mechanisms of nitrogen remobilization in poplar senescing leaves.

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.

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.

Deletion of a 1,049 bp sequence from the 5´ UTR upstream of the SiHEC3 gene induces a seed non-shattering mutation in sesame

Sesame is a labor intensive crop with limited mechanized harvesting mainly due to the seed shattering (SS) trait. In this study, we performed a genetic analysis of the seed-shattering resistance (SR) trait with a SR sesame mutant 12M07. Unlike the SS type, the parenchyma cells in the abscission zone of the 12M07 mutant are arranged loosely but adhere to the seed coat. Inheritance analysis of six generations derived from 12M07 (SR)×Xiangcheng Dazibai (SS) showed that the SR trait is recessive and controlled by a single gene pair. Association mapping of the F2 population with 888,619 variants (single-nucleotide polymorphisms (SNPs) and insertion-deletion (InDels)) and 31,884 structural variations (SVs) determined that only SV12002 in the 5´ upstream region of gene Sindi0765000 (named SiHEC3) in Chr.3 was significantly associated with the SR trait. SiHEC3 encodes the bHLH transcription factor. A 1,049 bp deletion occurred in the 5´ UTR of Sihec3 in 12M07. SiHEC3 is mainly expressed in developing placental tissues, with the expression peaking in capsules at 45 days after pollination. A dual-luciferase reporter assay in tobacco confirmed that the promoter activity of Sihec3 was reduced because of the deletion of the 1,049 bp promoter sequence. Protein–protein interaction network analysis showed that HEC3 is co-expressed with nine key proteins, such as SHATTERPROOF1 (SHP1) and SEEDSTICK (STK) which participate in the secondary wall biosynthesis of the abscission layer in plants. The findings of this study show the important function of Sihec3 corresponding with the SR trait and supply the genetic information for breeding new varieties that are amenable to mechanized harvesting in sesame and other crops.

Influence of the Cellular Ultrastructure and Enzyme Activity of the Leaf Sheath on Spontaneous Defoliation in Sugarcane

Spontaneous defoliation improves the harvesting efficiency and yield of sugarcane. Here, we investigated the ultrastructural changes and pectinase and cellulase activity in the third, fifth, and seventh leaf sheaths in four sugarcane varieties with varying spontaneous defoliation performance during maturation. At the early and middle stages of spontaneous defoliation, the cells in the abscission zones of the third, fifth, and seventh leaf sheaths were degrading. At the late stage, no complete organelles and hollow or broken spots in the cell walls were observed in the abscission zone cells of defoliation-prone varieties, while complete organelles and intact cell walls were present in the abscission zone cells at the same leaf positions in defoliation-resistant varieties. From the early to late stages, defoliation-prone varieties had higher pectinase activity in the abscission zones of the fifth and seventh leaf sheaths. At the early stage of defoliation, defoliation-prone varieties had significantly higher cellulase activity in the abscission zones of the third, fifth, and seventh leaf sheaths. Correlation analysis showed that the spontaneous defoliation rate was significantly positively correlated with pectinase activity in the leaf sheaths. In conclusion, the spontaneous defoliation of sugarcane was closely related to changes in cell morphology and pectinase activites in leaf sheaths.

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.

Suppression of a hexokinase gene SlHXK1 in tomato affects fruit setting and seed quality

Hexokinase is considered to be the key molecule in sugar signaling and metabolism. Here, we reported that silencing SlHXK1 resulted in a decrease in flower number, increased rate of flower dropping, abnormal thickening of the anther wall, and reduced pollen and seed viability. An anatomical analysis revealed the loss of small cells and abnormal thickening of anther walls in SlHXK1-RNAi lines. Treatment with auxin and 1-methylcyclopropene inhibited flower dropping from the pedicel abscission zone. qRT-PCR analysis revealed that the effect of SlHXK1 on abscission was associated with the expression levels of genes related to key meristem, auxin, ethylene, cell wall metabolism and programmed cell death. Pollen germination and pollen staining experiments showed that pollen viability was significantly reduced in the SlHXK1-RNAi lines. Physiological and biochemical analyses showed that hexokinase activity and starch content were markedly decreased in the transgenic lines. The expression of genes related to tomato pollen development was also suppressed in the transgenic lines. Although the RNAi lines eventually produced some viable seeds, the yield and quality of the seeds was lower than that of wild-type plants. Yeast two-hybrid and bimolecular fluorescence complementation assays showed that SlHXK1 interacted with SlKINγ. Furthermore, SlPIF4 inhibited the transcriptional expression of SlHXK1. In conclusion, our results demonstrate that SlHXK1 may play important roles in pollen, anther, seed and the pedicel abscission zone by affecting starch accumulation or cell wall synthesis, as well as by regulating the number of the transcripts of genes that are involved in auxin, ethylene and cell wall degradation.

A low carbon balance triggers Microvine inflorescence abscission at high temperatures

IntroductionGlobal warming is a major threat to yield sustainability in most crops, including grapevine. Whether or not grapevine fruitfulness is impaired by an imbalance between carbon supply and demand caused by high temperatures was investigated in the present study.MethodsFive experiments were conducted on Microvine, a natural mutant of grapevine that is insensitive to gibberellins, presents with a dwarf stature, and has continuous flowering along the vegetative axes. The last property was used to infer temporal patterns of inflorescence development from their spatial distribution at harvest. Two sets of plants, characterized by low or high levels of initial shoot vigor, were grown under contrasting day and night temperatures: 22°C/12°C and 30°C/20°C.Results and discussionThe rate of leaf development of the main shoot was stable, regardless of the initial vigor and temperature treatment. In contrast, the warm temperatures delayed the timing of flowering for low-vigor plants or the onset of ripening for high-vigor plants. Fruitfulness was impaired by high temperatures as a result of the abscission of young inflorescences (before the flowering stage). From a careful spatiotemporal analysis of cluster abscission, we concluded that inflorescence drop under elevated temperatures was triggered by the increase in plant carbon demand due to the oldest clusters starting to unload sugars. Elevated temperatures may have also lowered the carbohydrate supply in the zone of inflorescence abscission due to the higher leaf respiration while all organ growth demand was maintained. Interestingly, inflorescence abscission occurred earlier when whole-plant vigor was low and was followed by a recovery period, in spite of a lower non-structural sugar status than in high-vigor plants. Taken together, our results suggest that inflorescence abscission is linked to the variations of the carbon pool induced by changes in temperature and not to its absolute value. Our study, therefore, provides new hypotheses about the impacts of warm temperatures on the regulation of temperature-induced reproductive failure in grapevine.

Abscisic acid- and ethylene-induced abscission of yellow lupine flowers is mediated by jasmonates

The appropriate timing of organ abscission determines plant growth, development, reproductive success, and yield in relation to crop species. Among these, yellow lupine is an example of a crop species that loses many fully developed flowers, which limits the formation of pods with high-protein seeds and affects its economic value. Lupine flower abscission, similarly to the separation of other organs, depends on a complex regulatory network functioning in the cells of the abscission zone (AZ). In the present study, genetic, biochemical, and cellular methods were used to highlight the complexity of the interactions among strong hormonal stimulators of abscission, including abscisic acid (ABA), ethylene, and jasmonates (JAs) precisely in the AZ cells, with all results supporting that the JA-related pathway has an important role in the phytohormonal cross-talk leading to flower abscission in yellow lupine. Based on obtained results, we conclude that ABA and ET have positive influence on JAs biosynthesis and signaling pathway in time-dependent manner. Both phytohormones changes lipoxygenase (LOX) gene expression, affects LOX protein abundance, and JA accumulation in AZ cells. We have also shown that the signaling pathway of JA is highly sensitive to ABA and ET, given the accumulation of COI1 receptor and MYC2 transcription factor in response to these phytohormones. The results presented provide novel information about the JAs-dependent separation of organs and provide insight and details about the phytohormone-related mechanisms of lupine flower abscission.

Colleters in leaves of Mespilus germanica L. (Rosaceae): Micromorphology, histochemistry and fluorescence

New data on the micromorphology, histochemistry, and fluorescence of colleters on leaf structures at different stages of development (leaf blade, stipules, and petiole) of Mespilus germanica L. are presented. Colleters are found on the tips of the teeth of both young and mature leaf blades and stipules, less often on the petioles. The leaf veins approach the leaf tooth, but no vascularization was found in the colleter. On leaf structures inside the bud, young colleters were observed in the form of finger-shaped or rounded outgrowths consisting of isodiametric cells. Mature colleters are multicellular secretory structures that have a head on a short stalk. The central part of the head consists of densely packed parenchymal cells, which are surrounded by radially elongated palisade-like secretory cells covered with a cuticle. The main secretion process of the colleter falls on the period of active growth of leaf structures. The secreted substances accumulated in the intercellular spaces of the palisade-like cells of the head and then were released outside in the form of translucent vesicles. The secretion products were released when the cuticle was ruptured and spread over the surface of the head and tooth of the leaf blade and stipules. After the end of secretion, the sizes of the head of the colleter decreased, and an abscission zone appeared in the cells of the colleter stalk, along the border of which a fracture occurred when the head fell off. Histochemical analysis of the contents of the colleter showed the presence of polysaccharides, especially at a young age, substances of a phenolic nature and lipids at a more mature age. In the fluorescence spectrum of young leaf colleter secretion, a peak at 671–672 nm was observed upon excitation at 405 and 473 nm. The obtained data on Mespilus germanica L. colleter can be used in the taxonomy of Pyrinae and Rosaceae.

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.

LcERF10 functions as a positive regulator of litchi fruitlet abscission

Phytohormone ethylene is well-known in positive modulation of plant organ abscission. However, the molecular mechanism underlying ethylene-induced abscission remains largely unknown. Here, we identified an ethylene-responsive factor, LcERF10, as a key regulatory gene in litchi fruitlet abscission. LcERF10 was strongly induced in the fruitlet abscission zone (FAZ) during the ethylene-activated abscission. Silencing of LcERF10 in litchi weakened the cytosolic alkalization of the FAZ and reduced fruitlet abscission. Moreover, LcERF10 directly bound the promoter and repressed the expression of LcNHX7, a Na+/H+ exchanger that was down-regulated in FAZ following the ethylene-activated abscission and up-regulated after LcERF10 silencing. Additionally, ectopic expression of LcERF10 in Arabidopsis promoted the cytosolic alkalization of the floral organ AZ and accelerated the floral organ abscission. Collectively, our results suggest that the transcription factor LcERF10 plays a positive role in litchi fruitlet abscission.