Petal Abscission Research Articles

A multifaceted kinase axis regulates plant organ abscission through conserved signaling mechanisms

Plants have evolved mechanisms to abscise organs as they develop or when exposed to unfavorable conditions.1 Uncontrolled abscission of petals, fruits, or leaves can impair agricultural productivity.2,3,4,5 Despite its importance for abscission progression, our understanding of the IDA signaling pathway and its regulation remains incomplete. IDA is secreted to the apoplast, where it is perceived by the receptors HAESA (HAE) and HAESA-LIKE2 (HSL2) and somatic embryogenesis receptor kinase (SERK) co-receptors.6,7,8,9 These plasma membrane receptors activate an intracellular cascade of mitogen-activated protein kinases (MAPKs) by an unknown mechanism.10,11,12 Here, we characterize brassinosteroid signaling kinases (BSKs) as regulators of floral organ abscission in Arabidopsis. BSK1 localizes to the plasma membrane of abscission zone cells, where it interacts with HAESA receptors to regulate abscission. Furthermore, we demonstrate that YODA (YDA) has a leading role among other MAPKKKs in controlling abscission downstream of the HAESA/BSK complex. This kinase axis, comprising a leucine-rich repeat receptor kinase, a BSK, and an MAPKKK, is known to regulate stomatal patterning, early embryo development, and immunity.10,13,14,15,16 How specific cellular responses are obtained despite signaling through common effectors is not well understood. We show that the identified abscission-promoting allele of BSK1 also enhances receptor signaling in other BSK-mediated pathways, suggesting conservation of signaling mechanisms. Furthermore, we provide genetic evidence supporting independence of BSK1 function from its kinase activity in several developmental processes. Together, our findings suggest that BSK1 facilitates signaling between plasma membrane receptor kinases and MAPKKKs via conserved mechanisms across multiple facets of plant development.

Reactive Oxygen and Related Regulatory Factors Involved in Ethylene-Induced Petal Abscission in Roses.

Petal abscission affects the growth, development, and economic value of plants, but the mechanism of ethylene-ROS-induced petal abscission is not clear. Therefore, we treated roses with different treatments (MOCK, ETH, STS, and ETH + STS), and phenotypic characteristics of petal abscission, changed ratio of fresh weight, morphology of cells in AZ and the expression of RhSUC2 were analyzed. On this basis, we measured reactive oxygen species (ROS) content in petals and AZ cells of roses, and analyzed the expression levels of some genes related to ROS production and ROS scavenging. Ethylene promoted the petal abscission of rose through decreasing the fresh weight of the flower, promoting the stacking and stratification of AZ cells, and repressing the expression of RhSUC2. During this process, ethylene induced the ROS accumulation of AZ cells and petals mainly through increasing the expressions of some genes (RhRHS17, RhIDH1, RhIDH-III, RhERS, RhPBL32, RhFRS5, RhRAC5, RhRBOHD, RhRBOHC, and RhPLATZ9) related to ROS production and repressing those genes (RhCCR4, RhUBC30, RhSOD1, RhAPX6.1, and RhCATA) related to ROS scavenging. In summary, ROS and related regulatory factors involved in ethylene induced petal abscission in roses.

Deciphering the auxin-ethylene crosstalk in petal abscission through auxin influx carrier IpAUX1 of Itoh peony ‘Bartzella’

Auxin gradient on either side of the abscission zone play a crucial role in regulating organ abscission during plant senescence. Yet, the impact of auxin on the opening and senescence of cut peony flowers, specifically Itoh peony ‘Bartzella’, remains elusive. We employed the frozen section method to investigate the cell morphology within the petal abscission zone. Additionally, we quantified auxin levels via enzyme immunoassay and assessed the expression of genes related to indole-3-acetic acid (IAA) levels. Through our analyses, we pinpointed the critical gene, IpAUX1. Further investigation of IpAUX1 involved virus-induced gene silencing (VIGS) and transient overexpression techniques, allowing us to assess its role both in vitro flowers, through vacuum application, and in vivo flowers, via injection. Significant alterations were observed in the structure and cell morphology of the abscission zone correlating with the process of petal abscission, alongside noticeable auxin gradient. Silencing IpAUX1 led to a noticeable delay in petal abscission for both in vitro flowers and vivo flowers, while its transient overexpression hastened this process. This silencing effect was accompanied by a reduction in IAA levels around the abscission zone and a subsequent delay in the erasure of the auxin gradient. It also resulted in the downregulation of several genes: the auxin response factor IpARF1, ethylene synthesis-related genes IpACS1 and IpACO1, and cell wall hydrolysis-related genes IpPME1 and IpPG1. Conversely, the expression of genes involved in auxin synthesis gene IpYUCCA10, auxin efflux carrier IpPIN1, and the ethylene receptor IpETR1 saw significant upregulation. This study concludes that the auxin influx carrier IpAUX1 enhances the abscission zone cells' responsiveness to ethylene by modulating the auxin gradient. This action promotes cell hydrolysis within the abscission zone, thereby encouraging petal abscission. Our findings underscore the pivotal role of IpAUX1 as a positive regulator during the process of petal abscission.

Auxin efflux carrier PsPIN4 identified through genome-wide analysis as vital factor of petal abscission.

PIN-FORMED (PIN) proteins, which function as efflux transporters, play many crucial roles in the polar transportation of auxin within plants. In this study, the exogenous applications of auxin IAA and TIBA were found to significantly prolong and shorten the florescence of tree peony (Paeonia suffruticosa Andr.) flowers. This finding suggests that auxin has some regulatory influence in petal senescence and abscission. Further analysis revealed a total of 8 PsPINs distributed across three chromosomes, which could be categorized into two classes based on phylogenetic and structural analysis. PsPIN1, PsPIN2a-b, and PsPIN4 were separated into the "long" PIN category, while PsPIN5, PsPIN6a-b, and PsPIN8 belonged to the "short" one. Additionally, the cis-regulatory elements of PsPIN promoters were associated with plant development, phytohormones, and environmental stress. These genes displayed tissue-specific expression, and phosphorylation sites were abundant throughout the protein family. Notably, PsPIN4 displayed distinct and elevated expression levels in roots, leaves, and flower organs. Expression patterns among the abscission zone (AZ) and adjacent areas during various flowering stages and IAA treatment indicate that PsPIN4 likely influences the initiation of peony petal abscission. The PsPIN4 protein was observed to be co-localized on both the plasma membrane and the cell nucleus. The ectopic expression of PsPIN4 reversed the premature flower organs abscission in the Atpin4 and significantly protracted florescence when introduced to Col Arabidopsis. Our findings established a strong basis for further investigation of PIN gene biological functions, particularly concerning intrinsic relationship between PIN-mediated auxin polar.

Petal abscission is promoted by jasmonic acid-induced autophagy at Arabidopsis petal bases

In angiosperms, the transition from floral-organ maintenance to abscission determines reproductive success and seed dispersion. For petal abscission, cell-fate decisions specifically at the petal-cell base are more important than organ-level senescence or cell death in petals. However, how this transition is regulated remains unclear. Here, we identify a jasmonic acid (JA)-regulated chromatin-state switch at the base of Arabidopsis petals that directs local cell-fate determination via autophagy. During petal maintenance, co-repressors of JA signaling accumulate at the base of petals to block MYC activity, leading to lower levels of ROS. JA acts as an airborne signaling molecule transmitted from stamens to petals, accumulating primarily in petal bases to trigger chromatin remodeling. This allows MYC transcription factors to promote chromatin accessibility for downstream targets, including NAC DOMAIN-CONTAINING PROTEIN102 (ANAC102). ANAC102 accumulates specifically at the petal base prior to abscission and triggers ROS accumulation and cell death via AUTOPHAGY-RELATED GENEs induction. Developmentally induced autophagy at the petal base causes maturation, vacuolar delivery, and breakdown of autophagosomes for terminal cell differentiation. Dynamic changes in vesicles and cytoplasmic components in the vacuole occur in many plants, suggesting JA–NAC-mediated local cell-fate determination by autophagy may be conserved in angiosperms.

Sensitivity Consequences of Ethylene in Determining the Vase Life of Eremurus spectabilis and E. persicus

Foxtail lily (Eremurus), as a medicinal-ornamental geophyte, has recently emerged in the cut flower market as a novel, commercially significant specialty cut flower (SCF). However, there is limited information about the sensitivity to ethylene of foxtail lily species for managing the ethylene-mediated senescence to prolong the vase life and maintain the ornamental quality of this flower. The purpose of the current study was to compare the ethylene production rates and patterns, as well as the responses to exogenous ethylene and ethylene inhibitors, between two species, E. spectabilis and E. persicus, to better understand the role of ethylene in Eremurus inflorescence senescence. The results revealed that exogenous ethylene (10 μL L−1), as a pulsing or continuous method, dramatically accelerated petal wilting in E. spectabilis and petal abscission in E. persicus. Furthermore, the rate and patterns of endogenous ethylene production varied significantly among the two investigated species. Interestingly, E. persicus exhibited a higher rate of ethylene production than E. spectabilis on the first day after harvesting, but the reverse was true at the end of the vase life (Day 4 of the vase period). The results revealed that the treatments with ethylene inhibitors considerably improved the water relations and vase longevity of both foxtail lily species. The vase life of E. spectabilis was dramatically enhanced by silver thiosulfate complex (STS) treatment (0.2 mM pulse for 24 h) from 5 d (control) to 7 d. Furthermore, 1-methylcyclopropene (1-MCP) at 0.5 and 1.0 μL L−1 markedly improved water uptake, relative fresh weight, and water balance and extended the vase life of cut inflorescences by ~2 d in E. spectabilis and E. persicus, compared with those of control cut inflorescences, respectively. This research revealed that ethylene is involved in controlling the senescence of foxtail lily flowers, and two tested species exhibited distinct forms of ethylene sensitivity, including abscission type in E. persicus and wilting-type in E. spectabilis. Collectively, these findings suggest that ethylene is involved in the senescence of cut foxtail lily inflorescence and that ethylene inhibitors can prolong vase life.

Molecular characterization of the SAUR gene family in sweet cherry and functional analysis of PavSAUR55 in the process of abscission

Small auxin up RNA (SAUR) is a large gene family that is widely distributed among land plants. In this study, a comprehensive analysis of the SAUR family was performed in sweet cherry, and the potential biological functions of PavSAUR55 were identified using the method of genetic transformation. The sweet cherry genome encodes 86 SAUR members, the majority of which are intron-less. These genes appear to be divided into seven subfamilies through evolution. Gene duplication events indicate that fragment duplication and tandem duplication events occurred in the sweet cherry. Most of the members mainly underwent purification selection pressure during evolution. During fruit development, the expression levels of PavSAUR16/45/56/63 were up-regulated, and conversely, those of PavSAUR12/61 were down-regulated. Due to the significantly differential expressions of PavSAUR13/16/55/61 during the fruitlet abscission process, they might be the candidate genes involved in the regulation of physiological fruit abscission in sweet cherry. Overexpression of PavSAUR55 in Arabidopsis produced earlier reproductive growth, root elongation, and delayed petal abscission. In addition, this gene did not cause any change in the germination time of seeds and was able to increase the number of lateral roots under abscisic acid (ABA) treatment. The identified SAURs of sweet cherry play a crucial role in fruitlet abscission and will facilitate future insights into the mechanism underlying the heavy fruitlet abscission that can occur in this fruit crop.

The rose INFLORESCENCE DEFICIENT IN ABSCISSION-LIKE genes, RbIDL1 and RbIDL4, regulate abscission in an ethylene-responsive manner.

RbIDL1 and RbIDL4 are up-regulated in an ethylene-responsive manner during rose petal abscission and restored the Arabidopsisida-2 mutant abscission defect suggesting functional conservation of the IDA pathway in rose. Abscission is an ethylene-regulated developmental process wherein plants shed unwanted organs in a controlled manner. The INFLORESCENCE DEFICIENT IN ABSCISSION family has been identified as a key regulator of abscission in Arabidopsis, encoding peptides that interact with receptor-like kinases to activate abscission. Loss of function ida mutants show abscission deficiency in Arabidopsis. Functional conservation of the IDA pathway in other plant abscission processes is a matter of interest given the discovery of these genes in several plants. We have identified four members of the INFLORESCENCE DEFICIENT IN ABSCISSION-LIKE family from the ethylene-sensitive, early-abscising fragrant rose, Rosa bourboniana. All four are conserved in sequence and possess well-defined PIP, mIDa and EPIP motifs. Three of these, RbIDL1, RbIDL2 and RbIDL4 show a three-fourfold increase in transcript levels in petal abscission zones (AZ) during ethylene-induced petal abscission as well as natural abscission. The genes are also expressed in other floral tissues but respond differently to ethylene in these tissues. RbIDL1 and RbIDL4, the more prominently expressed IDL genes in rose, can complement the abscission defect of the Arabidopsis ida-2 mutant; while, promoters of both genes can drive AZ-specific expression in an ethylene-responsive manner even in Arabidopsis silique AZs indicating recognition of AZ-specific and ethylene-responsive cis elements in their promoters by the abscission machinery of rose as well as Arabidopsis.

Breeding Long Vase Life by Crossing and Selection for Five Generations in Dahlia (<i>Dahlia variabilis</i>) Cut Flowers, and Selection of Fourth-Generation Line 003-15 with Ultra-Long Vase Life

Genetic improvement of flower vase life is an important breeding target for ornamental plants. As the vase life of cut dahlia (Dahlia variabilis) flowers is very short, we initiated a conventional crossbreeding research program in 2014 to improve it. We evaluated the vase life of dahlia seedlings during summer (from July to early September) to develop dahlias that grow and bloom under high temperatures and have excellent vase life for Japanese summer conditions. Crossing and selection over five generations greatly improved vase life. The mean vase life increased from 4.4 days in the 1st generation, derived from 22 parental cultivars, to 8.0 days in the 5th generation, a net increase of 3.6 days. Mean vase life increased significantly by 1.6 days from the 4th to the 5th generation, indicating continued improvement. The mean vase life of the 12 lines selected from the 3rd and 4th generations ranged between 6.0 and 15.9 days in distilled water and from 7.8 to 14.6 days in GLA solution (10 g·L−1 glucose, 0.5 mL·L−1 CMIT/MIT [isothiazolinone derivatives], and 50 mg·L−1 aluminum sulfate). Vase life was further extended by 0.5 to 4.0 days using 6-benzylaminopurine (BA) sprays compared to GLA alone. In particular, the 4th-generation line 003-15 vase life was 13.8 to 15.9 days (2.5× that of ‘Kamakura’, a leading white dahlia cultivar in Japan) in distilled water, 12.0 to 14.6 days (1.8× to 2.2×) in GLA, and 13.9 to 15.3 days (1.7× to 1.9×) in GLA+BA in winter and spring. Cut flowers of line 003-15 harvested under high temperatures in July–August and at 28°C with GLA treatment also had long vase life. The pedigree of line 003-15 suggests that genes related to long vase life derived from ‘Micchan’ (with a long vase life) may have accumulated or duplicated in line 003-15. Finally, four selected lines, including 003-15, had high ethylene sensitivity, as 10 μL·L−1 ethylene treatment caused petal abscission in 2.0 to 2.8 days.

Comprehensive analyses of the proteome and ubiquitome revealed mechanism of high temperature accelerating petal abscission in tree peony

Tree peony (Paeonia suffruticosa Andrews) is a well-known ornamental plant with high economic value, but the short fluorescence is a key obstacle to its ornamental value and industry development. High temperature accelerates flower senescence and abscission, but the associated mechanisms are poorly understood. In this study, the tandem mass tag (TMT) proteome and label-free quantitative ubiquitome from tree peony cut flowers treated with 20 °C for 0 h (RT0), 20 °C or 28 °C for 60 h (RT60 or HT60) were examined based on morphological observation, respectively. Totally, 6970 proteins and 1545 lysine ubiquitinated (Kub) sites in 844 proteins were identified. Hydrophilic residues (such as glutamate and aspartate) neighboring the Kub sites were in preference, and 36.01% of the Kub sites were located on the protein surface. The differentially expressed proteins (DEPs) and Kub-DEPs in HT60 vs RT60 were mainly enriched in ribosomal protein, protein biosynthesis, secondary metabolites biosynthesis, flavonoid metabolism, carbohydrate catabolism, and auxin biosynthesis and signaling revealed by GO and KEGG analysis, accompanying the increase of endogenous abscisic acid (ABA) accumulation and decrease of endogenous indoleacetic acid (IAA) level. Additionally, the expression patterns of six enzymes (SAMS, ACO, YUC, CHS, ANS and PFK) putatively with Kub modifications were analyzed by proteome and real-time quantitative RT-PCR. The cell-free degradation assays showed PsSAMS and PsACO proteins could be degraded via the 26 S proteasome system in tree peony flowers. Finally, a working model was proposed for the acceleration of flower senescence and abscission by high temperature. In summary, all results contributed to understanding the mechanism of flower senescence induced by high temperature and prolonging fluorescence in tree peony.

The RhLOL1-RhILR3 module mediates cytokinin-induced petal abscission in rose.

In many plant species, petal abscission can be considered the final step of petal senescence. Cytokinins (CKs) are powerful suppressors of petal senescence; however, their role in petal abscission is ambiguous. Here, we observed that, in rose (Rosa hybrida), biologically active CK is accumulated during petal abscission and acts as an accelerator of the abscission process. Using a combination of reverse genetics, and molecular and biochemical techniques, we explored the roles of a LESION SIMULATING DISEASE1 (LSD1) family member RhLOL1 interacting with a bHLH transcription factor RhILR3 in CK-induced petal abscission. Silencing RhLOL1 delays rose petal abscission, while the overexpression of its ortholog SlLOL1 in tomato (Solanum lycopersicum) promotes pedicel abscission, indicating the conserved function of LOL1 in activating plant floral organ abscission. In addition, we identify a bHLH transcription factor, RhILR3, that interacts with RhLOL1. We show that RhILR3 binds to the promoters of the auxin signaling repressor auxin/indole-3-acetic acid (Aux/IAA) genes to inhibit their expression; however, the interaction of RhLOL1 with RhILR3 activates the expression of the Aux/IAA genes including RhIAA4-1. Silencing RhIAA4-1 delays rose petal abscission. Our results thus reveal a RhLOL1-RhILR3 regulatory module involved in CK-induced petal abscission via the regulation of the expression of the Aux/IAA genes.

Metabolome and transcriptome integration reveals insights into the process of delayed petal abscission in rose by STS.

The abscission of plant organs plays an important role in ensuring the normal life activities. Rose is one of the most important ornamental plants, and its premature abscission of petal has seriously affected the quality and commercial value. Silver Thiosulfate (STS) is an ethylene inhibitor, which is often used preservative to delay the senescence of fresh cut flowers. To understand the regulatory mechanism of petal abscission in rose by STS, integrative analysis of the metabolome and transcriptome profiles was performed in abscission zone (AZ) tissues of rose under different treatments (MOCK, STS, ETH, STS+ETH). The results showed that STS significantly delayed the petal abscission in phenotype and reduced the activity of two enzymes (pectinase and cellulase) associated with cell wall degradation in physiological level. STS affected the contents of five metabolites (shikonin, jasmonic acid, gluconolactone, stachyose and D-Erythrose 4-phosphate), and involved changes in the expression of 39 differentially expressed genes (DEGs) associated with these five metabolites. Five DEGs (LOC112192149, LOC112196726, LOC112189737, LOC112188495, and LOC112188936) were probably directly associated with the biosynthesis of shikonin, jasmonic acid, and D-Erythrose 4-phosphate. Meanwhile, the effect of STS on the abscission process significantly involved in the pentose phosphate pathway and amino acid biosynthesis pathway. In addition, STS had a greater effect on the transcription factors, phytohormone related DEGs represented by auxin and ethylene, DEGs related to disease resistance and amino acid, etc. Above all, STS negatively influences petal abscission of rose, these results maybe provide a reference for subsequent studies on petal abscission of rose by STS.

Integrative analysis of transcriptome, proteome, and ubiquitome changes during rose petal abscission.

Plant organ abscission is regulated by multiple physiological and biochemical processes. However, the transcriptional, translational, and post-translational modifications occurring during organ abscission have not been systematically investigated. In this study, we report transcriptome, proteome, and ubiquitome data for the abscission zone (AZ) of rose petals collected during petal shedding. We quantified 40,506 genes, 6,595 proteins, and 2,720 ubiquitinated proteins in rose petal AZ. Our results showed that during petal abscission, 1,496 genes were upregulated and 2,199 were downregulated; 271 proteins were upregulated and 444 were downregulated; and 139 ubiquitination sites in 100 proteins were upregulated and 55 ubiquitination sites in 48 proteins were downregulated. Extracellular levels of cell component proteins were significantly increased, while levels within protoplasts were significantly decreased. During petal abscission, transcript levels of genes involved in defense response, transport, and metabolism changed significantly. Levels of proteins involved in the starch and sucrose metabolism and phenylpropanoid biosynthesis pathways were significantly altered at both the transcript and protein levels. The transcriptional and translational upregulation of peroxidase (POD), in the phenylpropanoid biosynthesis, pathway may be associated with deposition of lignin, which forms a protective layer during petal abscission. Overall, our data provide a comprehensive assessment of the translational and post-translational changes that occur during rose petal abscission.

Salicylic Acid Enhances the Vase Life and Improves the Postharvest Attributes ¬¬— A Case Study of Antirrhinum majus L.

Antirrhinum majus L. is one of the most significant ornamental plants in the international flower industry, but has a relatively limited vase life, as evidenced by petal abscission and flower spike bending. The current study focuses on examining the efficacy of salicylic acid on the vase life and postharvest attributes of A. majus flower spikes. The spikes with the oldest floral bud at one day before anthesis stage were harvested and divided into 4 sets, with one set of spikes held in distilled water (DW) designated as control. The remaining three sets were supplemented with various concentrations of SA viz., 1, 2 and 3 mM. Among the concentrations studied, 2 mM was found to be the most promising SA concentration for increasing the postharvest performance of flowers of A. majus cut spikes. The enhanced vase life of A.majus spikes was characterised by increased floral diameter, a higher membrane stability index and elevated levels of total phenols and sugars as compared to the control. SA has been proven to suppress protein degradation and lipoxygenase activity during the vase life of flower spikes. Furthermore, SA-treated flower spikes with enhanced postharvest properties were shown to have higher levels of antioxidant enzymes such as superoxide dismutase, catalase and ascorbate peroxidase activity.

The JA pathway is rapidly down-regulated in petal abscission zones prior to flower opening and affects petal abscission in fragrant roses during natural and ethylene-induced petal abscission

Organ abscission is a developmental process regulated through changes in the abscission zone (AZ) and governed primarily by ethylene. In roses, the opening of flowers is also an ethylene-sensitive process possibly requiring changes at the AZ to facilitate petal movement. A study of the rose petal AZ transcriptome of the early-abscising fragrant rose, R. bourboniana, had indicated suppression of the jasmonic acid (JA) pathway in the AZ before abscission. Detailed investigation of 24 genes representing JA biosynthesis/perception/signalling revealed a rapid and substantial down-regulation of the entire JA pathway in the AZ prior to flower opening and abscission. Transcript levels of 17 genes encoding JA biosynthesis members of the PLD/LOX/AOS/AOC/OPR families and the receptor/signalling components of COI1/JAZ/MYC2/NINJA families decreased by 50–90% in petal AZ within 4 h of ethylene treatment as well as during natural field abscission (ethylene untreated). In contrast, R. hybrida flowers (which show delayed opening and abscission even after ethylene treatment) were much less affected in 10/24 genes while transcript levels of 9/24 JA pathway genes actually increased several fold during or just prior to abscission. JA treatment delayed flower opening as well as petal abscission by more than 24 h in R. bourboniana and also increased transcription of the JA pathway genes, unlike ethylene. The strong and rapid reduction of the entire JA pathway in the AZ in R. bourboniana flowers, prior to flower opening and petal abscission, suggests a negative role for JA in these processes with JA acting opposite to ethylene and possibly reducing ethylene sensitivity.

LcERF2 modulates cell wall metabolism by directly targeting a UDP-glucose-4-epimerase gene to regulate pedicel development and fruit abscission of litchi.

Elucidating the biochemical and molecular basis of premature abscission in fruit crops should help develop strategies to enhance fruit set and yield. Here, we report that LcERF2 contributes to differential abscission rates and responses to ethylene in Litchi chinensis (litchi). Reduced LcERF2 expression in litchi was observed to reduce fruit abscission, concurrent with enhanced pedicel growth and increased levels of hexoses, particularly galactose, as well as pectin abundance in the cell wall. Ecoptic expression of LcERF2 in Arabidopsis thaliana caused enhanced petal abscission, together with retarded plant growth and reduced pedicel galactose and pectin contents. Transcriptome analysis indicated that LcERF2 modulates the expression of genes involved in cell wall modification. Yeast one-hybrid, dual-luciferase reporter and electrophoretic mobility shift assays all demonstrated that a UDP-glucose-4-epimerase gene (LcUGE) was the direct downstream target of LcERF2. This result was further supported by a significant reduction in the expression of the A.thaliana homolog AtUGE2-4 in response to LcERF2 overexpression. Significantly reduced pedicel diameter and enhanced litchi fruit abscission were observed in response to LcUGE silencing. We conclude that LcERF2 mediates fruit abscission by orchestrating cell wall metabolism, and thus pedicel growth, in part by repressing the expression of LcUGE.

Petal abscission in fragrant roses is associated with large scale differential regulation of the abscission zone transcriptome

Flowers of fragrant roses such as Rosa bourboniana are ethylene-sensitive and undergo rapid petal abscission while hybrid roses show reduced ethylene sensitivity and delayed abscission. To understand the molecular mechanism underlying these differences, a comparative transcriptome of petal abscission zones (AZ) of 0 h and 8 h ethylene-treated flowers from R. bourboniana was performed. Differential regulation of 3700 genes (1518 up, 2182 down) representing 8.5% of the AZ transcriptome was observed between 0 and 8 h ethylene-treated R. bourboniana petal AZ. Abscission was associated with large scale up-regulation of the ethylene pathway but prominent suppression of the JA, auxin and light-regulated pathways. Regulatory genes encoding kinases/phosphatases/F-box proteins and transcription factors formed the major group undergoing differential regulation besides genes for transporters, wall modification, defense and phenylpropanoid pathways. Further comparisons with ethylene-treated petals of R. bourboniana and 8 h ethylene-treated AZ (R. hybrida) identified a core set of 255 genes uniquely regulated by ethylene in R. bourboniana AZ. Almost 23% of these encoded regulatory proteins largely conserved with Arabidopsis AZ components. Most of these were up-regulated while an entire set of photosystem genes was prominently down-regulated. The studies provide important information on regulation of petal abscission in roses.

Auxin Regulates Sucrose Transport to Repress Petal Abscission in Rose (Rosa hybrida).

Developmental transitions in plants require adequate carbon resources, and organ abscission often occurs due to competition for carbohydrates/assimilates. Physiological studies have indicated that organ abscission may be activated by Suc deprivation; however, an underlying regulatory mechanism that links Suc transport to organ shedding has yet to be identified. Here, we report that transport of Suc and the phytohormone auxin to petals through the phloem of the abscission zone (AZ) decreases during petal abscission in rose (Rosa hybrida), and that auxin regulates Suc transport into the petals. Expression of the Suc transporter RhSUC2 decreased in the AZ during rose petal abscission. Similarly, silencing of RhSUC2 reduced the Suc content in the petals and promotes petal abscission. We established that the auxin signaling protein RhARF7 binds to the promoter of RhSUC2, and that silencing of RhARF7 reduces petal Suc contents and promotes petal abscission. Overexpression of RhSUC2 in the petal AZ restored accelerated petal abscission caused by RhARF7 silencing. Moreover, treatment of rose petals with auxin and Suc delayed ethylene-induced abscission, whereas silencing of RhARF7 and RhSUC2 accelerated ethylene-induced petal abscission. Our results demonstrate that auxin modulates Suc transport during petal abscission, and that this process is regulated by a RhARF7-RhSUC2 module in the AZ.

Difference of ethylene production and response to ethylene in cut flowers of dahlia (Dahlia variabilis) cultivars

Cut dahlia flowers have a short vase life of 3–7 days, and some cultivars exhibit petal abscission, even inside of cardboard boxes during transport. This petal abscission is induced by ethylene in many cases. In the present study, we investigated the role of ethylene in dahlia flower senescence by comparing the responses to ethylene, ethylene inhibitors, and ethylene production among cultivars. Exogenous ethylene significantly accelerated petal abscission in seven cultivars and petal wilting in other five cultivars out of 12 cultivars. Whole florets and detached receptacles (with bracts) produced different amounts of ethylene; ethylene production was higher in ‘Carnelian’ and ‘Port Light Pair Beauty’ than ‘Heavenly Peace’ and ‘Purple Stone’. Onset of senescence was delayed in detached petals compared with attached petals, suggesting that petal abscission was induced by ethylene produced by ovary and receptacles. The ethylene action inhibitor 1-methylcyclopropene inhibited petal abscission and delayed petal wilting in eight cultivars. Moreover, the silver thiosulfate complex delayed petal wilting of ‘Carnelian’. Together, our findings suggested that ethylene plays a role in senescence of cut dahlia flowers and ethylene inhibitors can extend their vase life.

Functional analysis of SlNCED1 in pistil development and fruit set in tomato (Solanum lycopersicum L.)

Abscisic acid (ABA) is an important regulator of many plant developmental processes, although its regulation in the pistil during anthesis is unclear. We investigated the role of 9-cis-epoxycarotenoid dioxygenase (SlNCED1), a key ABA biosynthesis enzyme, through overexpression and transcriptome analysis in the tomato pistil. During pistil development, ABA accumulates and SlNCED1 expression increases continually, peaking one day before full bloom, when the maximum amount of ethylene is released in the pistil. ABA accumulation and SlNCED1 expression in the ovary remained high for three days before and after full bloom, but then both declined rapidly four days after full bloom following senescence and petal abscission and expansion of the young fruits. Overexpression of SlNCED1 significantly increased ABA levels and also up-regulated SlPP2C5 expression, which reduced ABA signaling activity. Overexpression of SlNCED1 caused up-regulation of pistil-specific Zinc finger transcription factor genes SlC3H29, SlC3H66, and SlC3HC4, which may have affected the expression of SlNCED1-mediated pistil development-related genes, causing major changes in ovary development. Increased ABA levels are due to SlNCED1 overexpresson which caused a hormonal imbalance resulting in the growth of parthenocarpic fruit. Our results indicate that SlNCED1 plays a crucial role in the regulation of ovary/pistil development and fruit set.