Location: Crops Pathology and Genetics Research2011 Annual Report
1a. Objectives (from AD-416)
Objective 1: Determine the effects of the plant growth regulator TDZ on the quality and display life of cut flowers and potted flowering plants. Objective 2: Develop effective and environmentally-sound treatments to protect cut rose flowers from postharvest loss due to infection by Botrytis cinerea. Sub-objectives: 2a) Determine optimal time for applying treatments to control Botrytis on cut roses; 2b) Evaluate efficacy of anti-fungal GRAS compounds for the control of Botrytis cinerea on cut roses. Objective 3: Determine molecular processes in flower senescence for the purposes of developing 'freshness' indicators for cut flowers and future genetic manipulation of flower senescence. Sub-objectives: 3a) Utilize virus-induced gene silencing (VIGS) technology to down-regulate the expression of NAC and MADS-box transcription factor genes and to test the effect of silencing these genes on flower longevity; 3b) Test a range of genes that are associated with floral aging and senescence for use as molecular indicators of freshness.
1b. Approach (from AD-416)
In Objective 1, we will test TDZ, a non-metabolized cytokinin, for its potential to extend the display life of cut flowers and potted flowering plants. In Objective 2, we will characterize the basic biology of Botrytis-rose flower interactions with a view to developing effective disease control measures. We will evaluate GRAS chemicals as they offer a cost effective and environmentally friendly alternative to current conventional fungicides. In Objective 3, we will identify regulatory genes that mediate retardation or acceleration of petal senescence. This will provide a foundation for the development of diagnostic molecular indicators of 'freshness' for cut flowers and for downstream analysis of the effects of loss of function of these genes on the genetic regulation of the senescence network. The integrated nature of this project will enhance the quality and longevity of flowers, leading to greater industry-wide profitability.
3. Progress Report
Postharvest losses and poor quality for floricultural crops usually results from the combination of infection by Botrytis cinerea, earlier leaf and flower senescence and abscission, and germplasm that lacks desirable postharvest qualities. This past year we continued to investigate, develop and implement strategies for improving postharvest performance for floriculture crops. Specific areas advanced included the following: 1). We continued to test the efficacy of thidiazuron (TDZ), a compound with plant hormone cytokinin-like activity, to improve longevity and to prevent leaf yellowing in potted plants such as lilies and tulips. A spray with low concentrations (5 to 10 ppm) of TDZ significantly extended the flower life of these potted plants. Leaves treated with TDZ delayed yellowing for more than two weeks. Furthermore, application of TDZ promoted ovary enlargement and permitted seed production. 2). We further investigated the potential of an environmentally-friendly household disinfectant bleach (sodium hypochlorite) to reduce Botrytis infection on minirose plants. Our preliminary data suggested that low concentrations of bleach solutions could reduce Botrytis infection on rose flowers when sprayed or applied as a dip treatment. 3). Flower senescence is under tight genetic control and involves changes in the gene expression. To identify a common set of genes that are up- or down-regulated during floral senescence in a broad range of flower species, we have developed a powerful microarray analysis that represents approximately 93,000 unique ESTs collected from genetic resource databases of petunia, tomato and potato. Gene expression analysis comparing young petals from senescing petal of petunia flowers suggest that more than a hundred genes are up-regulated or down-regulated during floral senescence, including some of regulatory genes that may control the initiation of flower senescence program. 4). We have developed Virus-Induced Gene Silencing (VIGS) technology in monocotyledon flower plant-gladiolus. We are continuing to investigate a large numbers of genes that may play key roles in the controlling of leaf and flower senescence and abscission. VIGS-silencing some of these genes delayed leaf and flower senescence and abscission. 5). Ethylene plays very important roles throughout growth and development, including regulation of flower senescence. We have generated petunia plants in which the dysfunctional ethylene receptor (etr1-1) is over-expressed under the control of a chemically-inducible system. The plants develop normally, and the life of the flowers is almost doubled when the plants or excised flowers are exposed to low concentrations of the inducer chemical (dexamethasone). This approach overcomes a variety of defects including poor germination, poor root growth and high susceptibility to disease when plants are constitutively expressing the trans-gene.
1. Flower senescence is a genetically controlled developmental process. To determine changes in the global gene expression during onset of floral senescence, ARS scientists at Davis, CA, have developed a Solanaceae micro-array including a total of 93,688 expressed sequence tags (EST) from four Solanum species (tomato, potato, pepper and petunia). We compared gene expression profiles of petunia petal tissues collected from different developmental stages ranging from two days prior to opening until seven days after opening (right before visible wilting). There were hundreds of up- or down-regulated sequences on day 2 and thousands on day 7 compared to day 0 samples. Proteins encoded by genes identified in these studies include many likely candidates for a role in the processes of petal senescence and resource remobilization including protein kinases that may be involved in senescence regulation, cysteine proteases and other enzymes that are associated with protein turnover, nucleases, and cell-wall associated proteins. Many transcription factors, including representatives of more than 10 different families (NAC, MYB, WRKY, ARF, HSF, C2H2-type zinc finger, homeodomain-leucine zipper, AP2/EREBP, bZIP, bHLH, and GRAS) were up- and/or down-regulated during onset of senescence, suggesting that a gene network may regulate floral senescence. Our studies demonstrate the utility of comparative gene profiling using a cross-species microarray approach for identifying genes with roles in the onset of flower senescence.
2. Controlling flower senescence by inducing expression of a mutant ethylene receptor etr1-1. Ethylene plays very important roles throughout growth and development, including regulation of flower senescence. Plants constitutively expressing the dysfunctional ethylene receptor (etr1-1) to reduce ethylene sensitivity dramatically extend flower longevity but show a variety of defects including poor germination, poor root growth and high susceptibility to disease. ARS scientists at Davis, CA, have generated transgenic petunia plants in which the etr1-1 is over-expressed under the control of a chemically-inducible system to block ethylene perception. The plants develop normally, and the life of the flowers is almost doubled when the plants or excised flowers are exposed to low concentrations of the inducer chemical (dexamethasone). This approach overcomes most defects associated with constitutively inhibition of the ethylene pathway and provides excellent means for controlling flower senescence.
3. Significant quality problems in ornamental potted and bedding plants. The quality of potted flowers is important to the ornamental industry. ARS scientists at Davis, CA, studied the effects of thidiazuron (TDZ) applications on the growth and development of potted Tulipa gesneriana ‘Christmas Dream’. Plants were treated with foliar sprays of a range of concentrations of TDZ (deionized water, 10µM, 100µM) at two developmental stages - four days prior to flower opening (stage 1) and the day flowers were just fully-opened (stage 2). Spray treatments with 10 to 100 µM TDZ at both stages resulted in a considerable delay in leaf yellowing compared to the controls (0 µM) and TDZ-treated tulip leaves tended to maintain higher chlorophyll contents through the lifecycle. More importantly, treatments with TDZ at 10 and 100 µM at both stages significantly increased the display life of potted tulip flowers, up to 10 days from 6 days in controls. In addition, TDZ-treated plants produced considerably larger (at least 2 fold) ovaries. Our results indicate significant potential for TDZ as a tool to improve the postharvest life of potted tulip plants.
Meir, S., Philosoph-Hadas, S., Sundaresan, S., Selvaraj, V.K., Burd, S., Ophir, R., Kochanek, B., Reid, M.S., Jiang, C., Lers, A. 2011. Identification of defense-related genes newly-associated with tomato flower abscission. Plant Signaling and Behavior. 6:4, 590-593.