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Title:   Author  item
                                            MEIR, SHIMON - Agricultural Research Organization, Volcani Centeritem
                                            PHILOSOPH-HADAS, SONIA - Agricultural Research Organization, Volcani Centeritem
                                            SUNDARESAN, SRIVIGNESH - Agricultural Research Organization, Volcani Centeritem
                                            SELVARAJ, VIJAY - Agricultural Research Organization, Volcani Centeritem
                                            BURD, SHAUL - Agricultural Research Organization, Volcani Centeritem
                                            KOCHANEK, BETTINA - Agricultural Research Organization, Volcani Centeritem
                                            REID, MICHAEL - University Of Californiaitem
                                            Jiang, Cai-Zhongitem
                                            LERS, AMNON - Agricultural Research Organization, Volcani Center
  Submitted to: Plant Physiology
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 5/1/2010
                                    Publication  Date: 12/1/2010
                                    Citation: Meir, S., Philosoph-Hadas, S., Sundaresan, S., Selvaraj, V.K., Burd, S., Kochanek, B., Reid, M.S., Jiang, C., Lers, A. 2010. Microarray analysis of the abscission-related transcriptome in tomato flower abscission zone in response to auxin depletion. Plant Physiology. 154:1929-1956.Interpretive Summary: Abscission, senescence and ripening are plant developmental processes that their timing is determined by tissue sensitivity to ethylene. The biological basis for this increased ethylene sensitivity is still not known, but it has been shown to be modulated also by other plant hormones. In abscission, the interplay between indole-3-acetic acid (IAA) and ethylene is well established. The generally accepted model is that a basipetal IAA flux through the abscission zone (AZ) prevents abscission by rendering the AZ insensitive to ethylene. The molecular mechanisms leading to increased tissue sensitivity to ethylene in response to IAA deficiency in the AZs are still unknown. The use of microarrays to analyze abscission-related gene expresseion was significantly promoted during the last years. The release of the Affymetrix GeneChip® Tomato Genome Array in 2005 provides a powerful analytical tool to explore the role of auxin in regulation of abscission in a species where abscission has been well characterized physiologically and biochemically. We describe here the results of this study in tomato (Solanum lycopersicumMill, cv. 'Shiran' 1335) flower AZ compared to the non-AZ (NAZ) tissue, using the Affymetrix gene chip, and examining changes in the transcriptome in response to auxin depletion, with or without of 1-MCP pretreatment. Our results describe global changes in gene expression in the tomato flower AZ tissue at an early stage following induction of the abscission process, when AZ becomes sensitive to ethylene, as well as at later stages in the process during execution of pedicel abscission and the development of a defense layer. Accordingly, the results allow the study of auxin-ethylene relations at a wide scope of the abscission process with the aid of the newly identified abscission-related genes.

The finding of this study will permit novel approaches to controlling abscission in horticultural and agricultural crops for improving there postharvest quality.
                                Technical Abstract: Abscission, the separation of organs from the parent plant, results in postharvest quality loss in many fresh produce. The process is initiated by changes in the auxin gradient across the abscission zone (AZ), is triggered by ethylene and may be accelerated by postharvest stresses. Although changes in gene expression have been correlated with the ethylene-mediated execution of abscission, there is almost no information on the molecular and biochemical basis of the increased AZ sensitivity to ethylene. We examined transcriptome changes in the tomato (Solanum lycopersicum Mill, cv. 'Shiran' 1335) flower AZ during the rapid acquisition of ethylene sensitivity following flower removal, which depletes the AZ from auxin, with or without exposure to the ethylene action inhibitor, 1-methylcyclopropene (1-MCP). Microarray analysis, using the Affymetrix Tomato GeneChip, revealed changes in expression, occurring prior to and during pedicel abscission, of many genes with possible regulatory functions. They included a range of auxin- and ethylene-related transcription factors (TFs), other TFs that are transiently induced 2 h after flower removal, indicating their involvement in the very early regulatory events of acquisition of ethylene sensitivity in the AZ, and a set of novel AZspecific genes. These results confirm our hypothesis that acquisition of ethylene sensitivity in the AZ is associated with altered expression of auxin-regulated genes, and further expand our knowledge of auxin-ethylene cross talk during the abscission process. The results also suggest a clear sequence of events and the genes involved, starting as auxin is depleted by flower removal and ending with pedicel abscission.


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