Genes associated with opening and senescence of the ephemeral flowers of Mirabilis jalapa

Authors: XU, XINJIA - UCD, DEPT. PLANT SCI.; GOOKIN, TIM - UCD, DEPT. PLANT SCI.; Jiang, Cai-Zhong; REID, MICHAEL - UCD, DEPT. PLANT SCI.

Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2007
Publication Date: 2/15/2007
Citation: Xu, X., Gookin, T.E., Jiang, C., Reid, M.S. Genes associated with opening and senescence of the ephemeral flowers of Mirabilis jalapa. Journal of Experimental Botany.

Interpretive Summary: Our objective is to search for molecular and genetic approaches to extend the life of ornamental flowers. To better understand what kinds of genes are involved in regulation of floral senescence, our intention for this project is to identify a gene or genes whose expression profile changes dramatically during onset of flower senescence in our model system, four o'clock. A modest ethylene climacteric accoompanies flower senescence in Mirabilis jalapa L., and exogenous ethylene accelerates the process. However, inhibitors of ethylene action and synthesis have little effect on the life-span of these ephemeral flowers. Treatment with a-amanitin, an inhibitor of DNA-dependent RNA synthesis, substantially delays the onset of senescence. This effect falls linearly between 7 and 8 hours after the start of flower opening. Subtractive hybridization was used to isolate transcripts that were up- and down-regulated during this critical period. We isolated 82 up-regulated and 65 down-regulated transcripts. The genes identified encode homologs of a range of transcription factors, and of proteins involved in protein turnover and degradation. Genes that were identified as being down-regulated during senescence showed a common pattern of very high expressioin during floral opening. These genes included a homolog CCA1, a 'clock' gene identified in Arabidopsis thaliana and an aspartyl protease. Up-regulated genes commonly showed a pattern of increase during the critical period (4-9 hours after opening), and some showed very strong up-regulatation. For example, the abundance of transcripts encoding a RING zinc finger protein increased more than 40,000 fold during the critical period. We isolated several transcription factors and other intriguing genes that provide new insights into the initiation and execution of flower senescence. In the long term, our results form the basis for molecular and genetic approaches to improve the potential life of many important floral crops.

Technical Abstract: A modest ethylene climacteric accompanies flower senescence in Mirabilis jalapa L., and exogenous ethylene accelerates the process. However, inhibitors of ethylene action and synthesis have little effect on the life-span of these ephemeral flowers. Treatment with a-amanitin, an inhibitor of DNA-dependent RNA synthesis, substantially delays the onset of senescence. This effect falls linearly between 7 and 8 hours after the start of flower opening. Subtractive hybridization was used to isolate transcripts that were up and down-regulated during this critical period. We isolated 82 up-regulated and 65 down-regulated transcipots. The genes identified encode homologs of a range of transcription factors, and of proteins involved in protein turnover and degradation. Real time quantitative RT-PCR was used to examine expression patterns of these genes during flower opening and senescence. Genes that were identified as being down-regulated during senescence showed a common pattern of very high expression during floral opening. These genes included a homolog CCA1, a 'clock' gene identified in Arabidopsis thaliana and an aspartyl protease. Up-regulated genes commonly showed a pattern of increase during the critical period (4-9 hours after opening), and some showed very strong up-regulation. For example, the abundance of transcripts encoding a RING zinc finger protein increased more than 40,000 fold during the critical period.