Tomato Abscission Research Articles

Tomato Pedicel Physical Characterization for Fruit-Pedicel Separation Tomato Harvesting Robot

To solve the problem of the lack of physical properties of pedicels and the changing pattern for designing the end-effector of tomato harvesting robot and different harvesting modes, research was conducted on the physical properties of tomato pedicels and their change patterns. Using a Universal TA texture analyzer, tensile, three-point bending, and shearing tests were performed on tomato pedicels in the early firm-ripening stage. The tomato variety used was Syngenta Spectrum, cultivated seasonally with two crops per year. Spring crop tomatoes were used in this study. The experimental results provide a theoretical basis for designing tomato harvesting robots across three harvesting modes. Tensile tests measured the pull-off force and tensile strength of the abscission zone with varying diameters. These results are crucial for designing robots using a tensile harvesting mode. The location of the tomato pedicel significantly affects the shearing force. A one-way test was conducted on the shearing part. The results showed that the shearing force and energy required for the proximal pedicel are significantly greater than for the distal pedicel. To reduce the shearing force and energy needed by the end-effector’s shearing mechanism on distal pedicels, a response surface test was conducted. Three factors were examined: shearing speed, angle, and distal pedicel diameter. Design–Expert software optimized these factors to minimize shearing energy and force, leading to the best shearing parameters for different distal pedicel diameters. From the three-point bending tests, the average maximum bending breaking force, bending modulus, and bending strength of the tomato abscission zone were determined. These findings offer a theoretical basis for designing tomato harvesting robots with a bending-type harvesting mode.

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.

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.

Involvement of IDA-HAE Module in Natural Development of Tomato Flower Abscission.

The unwanted detachment of organs such as flowers, leaves, and fruits from the main body of a plant (abscission) has significant effects on agricultural practice. Both timely and precise regulation of organ abscission from a plant is crucial as it influences the agricultural yield. The tomato (Solanum lycopersicum) has become a model system for research on organ abscission. Here, we characterized four tomato natural abscission variants named jointless (j), functionally impaired jointless (fij), functionally impaired jointless like (fij like), and normal joint (NJ), based on their cellular features within the flower abscission zones (AZ). Using eight INFLORESCENCE DEFICIENT IN ABSCISSION (SlIDA) genes and eight HAESA genes (SlHAE) identified in the genome sequence of tomato, we analyzed the pattern of gene expression during flower abscission. The AZ-specific expression for three tomato abscission polygalacturonases (SlTAPGs) in the development of flower AZ, and the progression of abscission validated our natural abscission system. Compared to that of j, fij, and fij like variants, the AZ-specific expression for SlIDA, SlIDL2, SlIDL3, SlIDL4, and SlIDL5 in the NJ largely corelated and increased with the process of abscission. Of eight SlHAE genes examined, the expression for SlHSL6 and SlHSL7 were found to be AZ-specific and increased as abscission progressed in the NJ variant. Unlike the result of gene expression obtained from natural abscission system, an in silico analysis of transcriptional binding sites uncovered that SlIDA genes (SlIDA, SlIDL6, and SlIDL7) are predominantly under the control of environmental stress, while most of the SlHSL genes are affiliated with the broader context in developmental processes and stress responses. Our result presents the potential bimodal transcriptional regulation of the tomato IDA-HAE module associated with flower abscission in tomatoes.

Auxin response and transport during induction of pedicel abscission in tomato

Auxin plays a central role in control of organ abscission, and it is thought that changes in the auxin gradient across the abscission zone are the primary determinant of the onset of abscission. The nature of this gradient, whether in concentration, flow, or perhaps in the response system has not conclusively been determined. We employed a DR5::GUS auxin response reporter system to examine the temporal and spatial distribution of the auxin response activity in response to developmental and environmental cues during pedicel abscission in tomato. In pedicels of young and fully open flowers, auxin response, as indicated by GUS activity, was predominantly detected in the vascular tissues and was almost entirely confined to the abscission zone (AZ) and to the distal portion of the pedicel, with a striking reduction in the proximal tissues below the AZ—a ‘step’, rather than a gradient. Following pollination and during early fruit development, auxin response increased substantially throughout the pedicel. Changes in GUS activity following treatments that caused pedicel abscission (flower removal, high temperature, darkness, ethylene, or N-1-naphthylphthalamic acid (NPA) treatment) were relatively minor, with reduced auxin response in the AZ and some reduction above and below it. Expression of genes encoding some auxin efflux carriers (PIN) and influx carriers (AUX⁄LAX) was substantially reduced in the abscission zone of NPA-treated pedicels, and in pedicels stimulated to abscise by flower removal. Our results suggest that changes in auxin flow distribution through the abscission zone are likely more important than the auxin response system in the regulation of abscission.

Plant Biology: Distinct New Players in Processing Peptide Hormones during Abscission

Flower organ abscission in Arabidopsis is regulated by a peptide hormone that is released from its precursor by a network of redundant subtilases. An exciting new study describes how drought-induced flower abscission in tomato is regulated similarly, but distinctly via a single, different subtilase that releases a very different peptide hormone.

Suppression of a Prolyl 4 Hydroxylase Results in Delayed Abscission of Overripe Tomato Fruits.

The tomato pedicel abscission zone (AZ) is considered a model system for flower and fruit abscission development, activation, and progression. O-glycosylated proteins such as the Arabidopsis IDA (INFLORESCENCE DEFICIENT IN ABSCISSION) peptide and Arabinogalactan proteins (AGPs) which undergo proline hydroxylation were demonstrated to participate in abscission regulation. Considering that the frequency of occurrence of proline hydroxylation might determine the structure as well the function of such proteins, the expression of a tomato prolyl 4 hydroxylase, SlP4H3 (Solanum lycopersicum Prolyl 4 Hydroxylase 3) was suppressed in order to investigate the physiological significance of this post-translational modification in tomato abscission. Silencing of SlP4H3 resulted in the delay of abscission progression in overripe tomato fruits 90 days after the breaker stage. The cause of this delay was attributed to the downregulation of the expression of cell wall hydrolases such as SlTAPGs (tomato abscission polygalacturonases) and cellulases as well as expansins. In addition, minor changes were observed in the mRNA levels of two SlAGPs and one extensin. Moreover, structural changes were observed in the silenced SlP4H3AZs. The fracture plane of the AZ was curved and not along a line as in wild type and there was a lack of lignin deposition in the AZs of overripe fruits 30 days after breaker. These results suggest that proline hydroxylation might play a role in the regulation of tomato pedicel abscission.

The Tomato Hybrid Proline-rich Protein regulates the abscission zone competence to respond to ethylene signals

The Tomato Hybrid Proline-rich Protein (THyPRP) gene was specifically expressed in the tomato (Solanum lycopersicum) flower abscission zone (FAZ), and its stable antisense silencing under the control of an abscission zone (AZ)-specific promoter, Tomato Abscission Polygalacturonase4, significantly inhibited tomato pedicel abscission following flower removal. For understanding the THyPRP role in regulating pedicel abscission, a transcriptomic analysis of the FAZ of THyPRP-silenced plants was performed, using a newly developed AZ-specific tomato microarray chip. Decreased expression of THyPRP in the silenced plants was already observed before abscission induction, resulting in FAZ-specific altered gene expression of transcription factors, epigenetic modifiers, post-translational regulators, and transporters. Our data demonstrate that the effect of THyPRP silencing on pedicel abscission was not mediated by its effect on auxin balance, but by decreased ethylene biosynthesis and response. Additionally, THyPRP silencing revealed new players, which were demonstrated for the first time to be involved in regulating pedicel abscission processes. These include: gibberellin perception, Ca2+-Calmodulin signaling, Serpins and Small Ubiquitin-related Modifier proteins involved in post-translational modifications, Synthaxin and SNARE-like proteins, which participate in exocytosis, a process necessary for cell separation. These changes, occurring in the silenced plants early after flower removal, inhibited and/or delayed the acquisition of the competence of the FAZ cells to respond to ethylene signaling. Our results suggest that THyPRP acts as a master regulator of flower abscission in tomato, predominantly by playing a role in the regulation of the FAZ cell competence to respond to ethylene signals.

Development and regulation of pedicel abscission in tomato

To shed unfertilized flowers or ripe fruits, many plant species develop a pedicel abscission zone (AZ), a specialized tissue that develops between the organ and the main body of the plant. Regulation of pedicel abscission is an important agricultural concern because pre-harvest abscission can reduce yields of fruit or grain crops, such as apples, rice, wheat, etc. Tomato has been studied as a model system for abscission, as tomato plants develop a distinct AZ at the midpoint of the pedicel and several tomato mutants, such as jointless, have pedicels that lack an AZ. This mini-review focuses on recent advances in research on the mechanisms regulating tomato pedicel abscission. Molecular genetic studies revealed that three MADS-box transcription factors interactively play a central role in pedicel AZ development. Transcriptome analyses identified activities involved in abscission and also found novel transcription factors that may regulate AZ activities. Another study identified transcription factors mediating abscission pathways from induction signals to activation of cell wall hydrolysis. These recent findings in tomato will enable significant advances in understanding the regulation of abscission in other key agronomic species.

Apple SVP Family MADS-Box Proteins and the Tomato Pedicel Abscission Zone Regulator JOINTLESS have Similar Molecular Activities

Pedicel abscission occurs widely in fruit-bearing plants to detach ripe, senescent or diseased organs, and regulation of abscission plays a substantial role in regulating yield and quality in fruit crops. In tomato, development of pedicel abscission zones (AZs) requires the MADS-box genes JOINTLESS (J), MACROCALYX (MC) and SlMBP21. In other plants, however, the involvement of MADS-box genes in pedicel abscission remains unclear. Here, we used genetic and biochemical methods to characterize apple J homologs in the context of the regulation of abscission in tomato. We identified three genes encoding two J homologs, MdJa and MdJb. Similarly to J, MdJa and MdJb interacted with MC and SlMBP21, but their interactions differed slightly: like J, MdJb formed a multimer (probably a tetramer) with SlMBP21; however, MdJa formed multimers to a lesser extent. Ectopic expression of MdJb in a J-deficient tomato mutant restored development of functional pedicel AZs, but ectopic expression of MdJa did not complement j mutants. Introduction of MdJb also restored expression of J-dependent genes in the mutant, such as genes for polygalacturonase, cellulase and AZ-specific transcription factors. These results suggest a potentially conserved mechanism of pedicel AZ development in apple and other plants, regulated by MADS-box transcription factors.

A KNOTTED1-LIKE HOMEOBOX protein regulates abscission in tomato by modulating the auxin pathway.

A gene encoding a KNOTTED1-LIKE HOMEOBOX PROTEIN1 (KD1) is highly expressed in both leaf and flower abscission zones. Reducing the abundance of transcripts of this gene in tomato (Solanum lycopersicum) by both virus-induced gene silencing and stable transformation with a silencing construct driven by an abscission-specific promoter resulted in a striking retardation of pedicel and petiole abscission. In contrast, Petroselinum, a semidominant KD1 mutant, showed accelerated pedicel and petiole abscission. Complementary DNA microarray and quantitative reverse transcription-polymerase chain reaction analysis indicated that regulation of abscission by KD1 was associated with changed abundance of genes related to auxin transporters and signaling components. Measurement of auxin content and activity of a DR5::β-glucuronidase auxin reporter assay showed that changes in KD1 expression modulated the auxin concentration and response gradient in the abscission zone.

Overexpression of a novel MADS-box gene SlFYFL delays senescence, fruit ripening and abscission in tomato

MADS-domain proteins are important transcription factors involved in many biological processes of plants. In our study, a tomato MADS-box gene, SlFYFL, was isolated. SlFYFL is expressed in all tissues of tomato and significantly higher in mature leave, fruit of different stages, AZ (abscission zone) and sepal. Delayed leaf senescence and fruit ripening, increased storability and longer sepals were observed in 35S:FYFL tomato. The accumulation of carotenoid was reduced, and ethylene content, ethylene biosynthetic and responsive genes were down-regulated in 35S:FYFL fruits. Abscission zone (AZ) did not form normally and abscission zone development related genes were declined in AZs of 35S:FYFL plants. Yeast two-hybrid assay revealed that SlFYFL protein could interact with SlMADS-RIN, SlMADS1 and SlJOINTLESS, respectively. These results suggest that overexpression of SlFYFL regulate fruit ripening and development of AZ via interactions with the ripening and abscission zone-related MADS box proteins.

Temporal and Spatial Distribution of Auxin Response Factor Genes During Tomato Flower Abscission

Abscission facilitates growth and reproduction and improves plant defenses against pathogens. This tightly regulated process is triggered by environmental cues and hormones such as ethylene and auxin. Because auxin is crucial for abscission, auxin response factors (ARFs) may play important roles in this process. Here, we examined changes in gene expression during abscission in tomato, focusing on regulation of genes encoding ARFs. Specifically, we analyzed the pattern of ARF gene expression in tomato flower pedicel explants treated with ethylene, the ethylene blocker 1-methylcyclopropene (1-MCP), or auxin to determine how auxin and ethylene affect ARF gene expression. In addition, we examined the spatial and temporal distribution of IAA during abscission by examining transgenic tomato plants expressing an IAA-inducible promoter fused to the GUS reporter gene (the P5::GUS ‘Chico III’ line). Flower removal from the explants quickly induced abscission by ethylene, which was inhibited by exogenous auxin or 1-MCP. During early abscission, auxin (or 1-MCP) regulated the expression of various ARFs, including ARF1, 2, 3, 4, 5, 7, 8-1, 9, 11, 12, 13, 13-1, 14, and 17, whereas ethylene had the opposite effect on most of these genes. Further analysis shows that during this stage, auxin may mediate the expression of ARF8-1, 9, 11, 12, 13, 13-1, and 14, whereas ethylene may mediate ARF13-1. During the later stage of abscission, ARF2, 8, 10, 11, and 19 were upregulated, and 8-1, 12, 13, and 13-1 were downregulated, compared with nonabscising parts of plants. Fluorometric GUS analysis indicated that GUS activity in the abscission zone remained stable at 4 h and sharply decreased after 8 h until abscission was complete (32 h).

The effect of calcium on auxin depletion-induced tomato ( Lycopersicon esculentum Mill.) pedicel abscission

Indole-3-acetic acid (IAA) and calcium are the most important factors that instigate plant organ abscission. This study aimed to elucidate the mechanisms that underlie the effects of IAA and calcium on delayed abscission in tomato. The results showed a clear trend towards reduced abscission rates with increased concentrations of IAA, and the applications on pedicel proximal or distal side also resulted in a different abscission. IAA combined with calcium significantly improved inhibition in contrast to IAA only, while IAA combined with magnesium exhibited little increased inhibition. 1-NNaphthylphthalamic acid (NPA), a polar auxin transport inhibitor, accelerated the abscission. IAA transported basipetally through an assay with 4 mm long pedicel sections indicated that the average transport intensity of [ 3 H]-IAA applied to the distal pedicel end was 65 Bq h –1 and the average velocity was 5.29 mm h -1 . When the proximal side was incubated in [ 3 H]-IAA, its average transport intensity reduced to 19.53 Bq h –1 and the average velocity was only 1.92 mm h -1 . Calcium treatment enhanced IAA transportation, as shown by significantly enhancing the transport intensity, but it had no effect on velocity. Keywords: Indole-3-acetic acid (IAA), calcium, abscission, tomato

Evaluation of the expression of internal control transcripts by real-time RT-PCR analysis during tomato flower abscission

Many investigations of the abscission mechanisms in plants are based on gene expression studies. Quantitative real-time RT-PCR (qRT-PCR) is widely and increasingly used for mRNA quantification, and the results are typically referenced to an internal control gene to avoid bias. We investigated the suitability of twelve tomato (Lycopersicon esculentum Mill. var. Liaoyuanduoli) housekeeping genes during hormone, high salt and temperature-induced abscission. The free software-based applications NormFinder and qBase PLUS were used to statistically identify the best internal controls for a given set of biological samples. The expression stability of a number of housekeeping genes were validated during tomato abscission. The two most suitable reference genes for the commonly used treatments of the major hormones related to abscission are TBP and RPL8. In some cases, more than three reference genes may be required, depending on the type of samples being compared. Four suitable reference genes (TBP/DNAj/RPL8/EXPRESSION) are recommended for more complex analysis, such as hormone and bio-stress induced abscission samples.

IDA-like gene expression in soybean and tomato leaf abscission and requirement for a diffusible stelar abscission signal

The stimulatory and inhibitory role of ethylene and auxin, respectively, in leaf abscission (leaf drop) is well documented. More recently, IDA (INFLORESCENCE DEFICIENT IN ABSCISSION) peptides and their putative interacting receptor-like-kinase partners, HAESA and HAESA-like2, were shown to be essential components in Arabidopsis floral organ abscission. Prior to research on IDA, it was reported that bean (Phaseolus vulgaris) leaf abscission required a diffusible signal that emanated from the vascular tissue. We were interested in determining whether the IDA signalling path might regulate abscission in plants other than Arabidopsis and whether IDA might act as a diffusible signal in abscission. Quantitative polymerase chain reaction was used to monitor gene expression and a GUS reporter gene construct used to determine the need for a diffusible signal in tomato. We identified 12 IDA-like and 11 HAESA-like genes in soybean (Glycine max) and monitored their gene expression in abscission in relation to the expression of several cell-wall-modifying proteins and aminocyclopropane-1-carboxylic acid synthases. Ethylene evoked the expression of several IDA-like genes in abscission zones (AZ), but also to a lesser degree in the adjacent petiole tissue. Surprisingly, IDA-like gene expression was very high in senescent soybean leaves. We identified five IDA-like genes in tomato (Solanum lycopersicum). Only one IDA-like gene was expressed in the tomato AZ and its expression was approximately equal in the AZ and petioles, but no IDA-like gene showed significant expression in leaves at up to 96 h of exposure to ethylene. IDA-like gene expression is up-regulated during soybean and tomato abscission but up-regulation was not limited to the AZ. Cell separation in the AZ cortex of tomato does not require a diffusible signal emanating from the stele. A role for IDA in soybean and tomato leaf abscission is discussed.

Programmed cell death occurs asymmetrically during abscission in tomato.

Abscission occurs specifically in the abscission zone (AZ) tissue as a natural stage of plant development. Previously, we observed delay of tomato (Solanum lycopersicum) leaf abscission when the LX ribonuclease (LX) was inhibited. The known association between LX expression and programmed cell death (PCD) suggested involvement of PCD in abscission. In this study, hallmarks of PCD were identified in the tomato leaf and flower AZs during the late stage of abscission. These included loss of cell viability, altered nuclear morphology, DNA fragmentation, elevated levels of reactive oxygen species and enzymatic activities, and expression of PCD-associated genes. Overexpression of antiapoptotic proteins resulted in retarded abscission, indicating PCD requirement. PCD, LX, and nuclease gene expression were visualized primarily in the AZ distal tissue, demonstrating an asymmetry between the two AZ sides. Asymmetric expression was observed for genes associated with cell wall hydrolysis, leading to AZ, or associated with ethylene biosynthesis, which induces abscission. These results suggest that different abscission-related processes occur asymmetrically between the AZ proximal and distal sides. Taken together, our findings identify PCD as a key mechanism that occurs asymmetrically during normal progression of abscission and suggest an important role for LX in this PCD process.

Transgenic analysis of tomato endo‐β‐1,4‐glucanase gene function. Role of cel1 in floral abscission

SummaryEndo‐β‐1,4‐glucanase (EGase) expression in ripening tomato fruit and abscising tomato flowers reflects the overlapping accumulation of structurally divergent gene transcripts, including EGase1 (Cel1) and EGase2 (Cel2). Transgenic plants in which cel1 expression was specifically inhibited were evaluated in order to assess the potential role(s) played by Cel1 during fruit ripening and floral abscission. The constitutive expression of an antisense cel1 gene driven by the 35S promoter of cauliflower mosaic virus resulted in the reduction of Cel1 mRNA to trace levels in both ripening fruit and abscising abscission zones of transgenic tomato plants. Transgenic fruit in which cel1 expression was reduced to less than 0.1% of wild‐type levels exhibited normal growth and softening behaviour. Transgenic floral abscission zones expressing 5–7% of wild‐type levels of Cel1 mRNA exhibited an incidence of abscission reduced by up to one third. The incomplete loss of abscission ability by transgenic flowers may indicate that the contribution of Cel1 activity is insufficient to account for all floral abscission and attests to the presence in tomato abscission zones of additional cell wall hydrolase activities, including Cel2.

The gene promoter for a bean abscission cellulase is ethylene-induced in transgenic tomato and shows high sequence conservation with a soybean abscission cellulase.

Bean leaf abscission (organ separation) correlates with the de novo accumulation of a pI9.5 cellulase and its mRNA. Overlapping genomic clones encoding the bean abscission cellulase (BAC) were isolated and partially sequenced. In addition, a genomic clone for a soybean abscission cellulase (SAC) was identified and the sequence compared to the BAC genomic sequence. Two 5'-upstream regions are particularly well conserved in the two sequences. Of special interest here is the region between -1 and -200 in the BAC promoter which is highly conserved in the SAC gene. Particle gun bombardment with a BAC promoter construct containing 210 bp of BAC sequence 5' to the transcription start site was sufficient to drive abscission-specific and ethylene and auxin-regulated transient expression in bean. In addition to the transient expression assay, expression was examined in stably transformed tomato. A similar -210 bp BAC promoter construct supported a low level of ethylene-inducible reporter gene expression in tomato leaf abscission zones and adjacent petioles but not in ethylene-treated stem tissue or fruit. Expression from the -210 promoter in tomato abscission zones was inhibited by silver thiosulfate, an ethylene action inhibitor, and was partially inhibited by treatment with auxin.