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Title:   Author  item
                                            Jiang, Cai-Zhongitem
                                            FENG, LU - DEPT PLANT SCI, UC DAVISitem
                                            IMSABAI, WACHIRAYA - DEPT PLANT SCI, UC DAVISitem
                                            MEIR, SHIMON - ARO,VOLCANI CNTR,ISRAELitem
                                            REID, MICHAEL - DEPT PLANT SCI, UC DAVIS
  Submitted to: Journal of Experimental Botany
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 1/16/2008
                                    Publication  Date: 3/2/2008
                                    Citation: Jiang, C., Feng, L., Imsabai, W., Meir, S., Reid, M.S. 2008. Silencing polygalacturonase expression inhibits tomato petiole abscission. Journal of Experimental Botany. Vol. 59, No. 4, pp. 973-979.Interpretive Summary: In the postharvest handling of ornamentals and other horticultural crops, premature abscission can often result in significant loss of quality and longevity.  To overcome the problem, many crops are treated with chemicals to delay or prevent abscission.  It is well established that treatments with various auxins and/or ethylene inhibitors, significantly prevent leaf and floret abscission in ornamentals.  Although these chemical treatments provide an interim solution to the abscission problem in ornamentals, the long-term solution is in the development, through conventional or molecular breeding, of cultivars that are not prone to abscission.
We used Virus Induced Gene Silencing (VIGS) as a tool for functional analysis of cell-wall associated genes that have been suggested to be involved in leaf abscission.  Tobacco rattle virus (TRV) is an effective vector for VIGS in tomato (Lycopersicon esculentum).  To establish a tomato system for this study, we tested different varieties under different growth conditions.  Silencing was more efficient when the plants were grown at 22°C than when they were grown at 20°C or 25°C.  The photobleaching phenotype resulting from silencing phytoene desaturase (PDS) varied, depending on cultivar, from barely visible, to photobleaching of entire leaves.  To study the function of abscission-related genes, we used a purple transgenic tomato line constitutively expressing the maize anthocyanin regulatory gene, Leaf color (Lc).  Silencing Lc expression in this line resulted in reduced anthocyanin production (reversing the color from purple to green), thus providing a convenient silencing ‘reporter’.  Silencing tomato abscission-related polygalacturonases (TAPGs) using a TAPG1 fragment delayed abscission, and increased break strength of the abscission zone in explants treated with 1 μL.L-1 ethylene.  The abundance of TAPG1 transcripts in the green (silenced) abscission zone (AZ) tissues was less than 1% of that in the purple (non-silenced) controls.  As we used a highly homologous region for all five TAPGs we assume that the effect of delayed abscission is the result of silencing the five genes in this family.  In contrast silencing abscission-related expansins (EXP11 and EXP12) and cellulases (Cel1 and Cel2) had no discernible effect on break strength, even when the two cellulase genes were silenced concurrently.  Simultaneous silencing of TAPG1 and Cel1 was no more effective than silencing TAPG1 alone.  The data demonstrate the importance of TAPGs in the abscission of leaf petioles. 
The finding of this study will permit novel approaches to controlling abscission in horticultural and agricultural crops for improving there postharvest quality.
                                Technical Abstract: We used Virus Induced Gene Silencing (VIGS) as a tool for functional analysis of cell-wall associated genes that have been suggested to be involved in leaf abscission.  Tobacco rattle virus (TRV) is an effective vector for VIGS in tomato (Lycopersicon esculentum).  Silencing was more efficient when the plants were grown at 22°C than when they were grown at 20°C or 25°C.  The photobleaching phenotype resulting from silencing phytoene desaturase (PDS) varied, depending on cultivar, from barely visible, to photobleaching of entire leaves.  To study the function of abscission-related genes, we used a purple transgenic tomato line constitutively expressing the maize anthocyanin regulatory gene, Leaf color (Lc).  Silencing Lc expression in this line resulted in reduced anthocyanin production (reversing the color from purple to green), thus providing a convenient silencing ‘reporter’.  Silencing tomato abscission-related polygalacturonases (TAPGs) using a TAPG1 fragment delayed abscission, and increased break strength of the abscission zone in explants treated with 1 μL.L-1 ethylene.  The abundance of TAPG1 transcripts in the green (silenced) abscission zone (AZ) tissues was less than 1% of that in the purple (non-silenced) controls.  As we used a highly homologous region for all five TAPGs we assume that the effect of delayed abscission is the result of silencing the five genes in this family.  In contrast silencing abscission-related expansins (EXP11 and EXP12) and cellulases (Cel1 and Cel2) had no discernible effect on break strength, even when the two cellulase genes were silenced concurrently.  Simultaneous silencing of TAPG1 and Cel1 was no more effective than silencing TAPG1 alone.  The data demonstrate the importance of TAPGs in the abscission of leaf petioles.


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