2013 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. Formerly 5306-13210-002-00D (11/08).
Postharvest losses and poor quality for ornamental crops often result from a combination of factors which includes, disease damages caused by Botrytis cinerea, shorter shelf life caused by earlier senescence and germplasm that lacks desirable postharvest qualities. This past year, ARS scientists in Davis, California, continued to investigate, develop and implement strategies for improving postharvest performance for ornamental crops. Specific areas advanced included the following:
1) Generated petunia plants in which the dysfunctional ethylene receptor is over-expressed under the control of a chemically-inducible system. The plants develop normally, and flower longevity is almost doubled when the chemical inducer is used. This approach is able to convert the ethylene sensitive flowers into ethylene insensitive ones. ARS scientists in Davis, California, conducted the global gene expression analysis used a powerful microarray technology and these transgenic plants. Results indicated that transcripts of many putative genes encoding transcription factors were down-regulated at the early stage. In addition, putative genes involved in gibberellin biosynthesis, response to jasmonic acid/gibberellins stimulus, cell wall modification, ethylene biosynthesis, and cell death were down-regulated, suggesting that those transcription factors down-regulated at early stage might exert a major role in regulating the senescence process. Furthermore, when these transgenic petunia plants were inoculated with Botrytis cinerea, disease symptoms on detached leaves and flowers or intact plants were dramatically reduced.
2) 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 ethylene insensitive flower species, ARS scientists in Davis, California, have developed Virus-Induced Gene Silencing (VIGS) technology in ethylene insensitive, extremely short flower longevity (approximately 16 hours from opening to wilting) of flowering plants. Results from this study suggested that co-silencing of endogenous anti-viral proteins may increase the range of taxa that are amenable to the use of VIGS for functional gene analysis.
3) Regulatory transcription factors play an important role in controlling flower senescence. ARS scientists in Davis, California, found that the transcription level of several classes of transcription factors were upregulated during flower aging process. Silencing one of them by using virus-induced gene silencing (VIGS) method extended flower longevity significantly (from 4 days to 6 days in detached flowers). The expression of ethylene biosynthesis genes, a key abscisic acid (ABA) biosynthesis gene, and senescence reporters (SAG12, and SAG29) was down regulated in the silenced flowers. Furthermore, the transcript level of this regulatory gene in the normal petunia flowers was induced by hormone (ethylene, ABA) and abiotic stress conditions (dehydration, sodium chloride [NaCl] and cold). The results suggest that this transcription factor regulates flower senescence through both ethylene and ABA pathways.
Development of Virus-Induced Gene Silencing (VIGS) technology in ethylene insensitive flowers for functional gene analysis. 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 ethylene insensitive flower species and functional analysis of these genes, ARS scientists in Davis, California, have developed Virus-Induced Gene Silencing (VIGS) technology in ethylene insensitive, extremely short flower longevity (approximately 16 hours from opening to wilting) of flower plant. Results from this study suggested that co-silencing of endogenous anti-viral proteins may increase the range of taxa, including ethylene insensitive species, that are amenable to the use of VIGS for functional gene analysis. This technology provides an effective tool to solve what regulates flower senescence and to extend flower longevity in ethylene-insentitive flowers for the ornamental industry.
Generation of ethylene insensitive flowers by inducing expression of a mutant ethylene receptor. Ethylene plays very important roles throughout growth and development, including regulation of flower senescence. Plants expressing the dysfunctional ethylene receptor 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 in Davis, California, have generated transgenic petunia plants in which the mutated receptor is over-expressed under the control of a chemically-inducible system to block ethylene perception. The plants develop normally, and flower longevity is doubled when the chemical inducer is used. Furthermore, when these transgenic petunia plants were inoculated with Botrytis cinerea, disease symptoms on detached leaves and flowers or intact plants were dramatically reduced. This innovative approach overcomes most of defects associated with constitutively inhibition of the ethylene pathway, being able to convert the ethylene sensitive flowers into ethylene insensitive ones, and provides excellent means for controlling flower senescence and improving disease resistance.
Wang, H., Liu, G., Li, C., Jiang, C., Reid, M.S., Zhang, Z., Powell, A.L. 2013. Defense responses regulated by jasmonate and delayed senescence caused by ethylene receptor mutation contribute to tolerance of petunia to Botrytis cinerea. Molecular Plant Pathology. 14(5):453-469.
Deng, L., Jiang, C., Mu, W., Wang, Q. 2013. Influence of 1-MCP treatments on eating quality and consumer preferences of ‘Qinmei’ kiwifruit during shelf life. Journal of Food Science and Technology. DOI 10.1007/s13197-013-0986-y.
Wang, H., Stier, G., Lin, J., Liu, G., Zhang, Z., Chang, Y., Reid, M.S., Jiang, C. 2013. Transcriptome changes associated wtih delayed flower senescence on transgenic petunia by inducing expression of etr1-1, a mutant ethylene receptor. PLoS One. 8(7):1-14.