The senescence of flower petals is associated with increased synthesis of the phytohormone ethylene, which in turn serves to initiate and regulate the processes of programmed cell death. This research aims to investigate the molecular mechanisms involved in the induction of ethylene synthesis, and determine how ethylene acts to initiate this developmental program. The initial experiments have focused on identifying senescence-related mRNAs and characterizing their temporal, spatial, and hormonal regulation. Among these senescence-related transcripts are those encoding enzymes in the ethylene biosynthetic pathway including 1- aminocyclopropane- 1 carboxylate synthase and the ethylene forming enzyme. Expression of antisense RNAs of senescence-related genes will be used to determine if these genes are essential for programmed cell death. The PI will define the cis-acting elements involved in the regulation of tissue-specific and/or ethylene- regulated expression of petal senscence-related genes and - glucuronidase and the PI will evaluate the expression of this reportedr gene in response to developmental factors and ethylene in transgenic plants and transient assays. Identification of regulatory sequences will allow us to screen expression libraries of senescing petal mRNAs for clones whose products specifically bind to these DNA sequences. Aside from questions concerning the developmental biology of programmed cell death, these experiments will identify intermediates in the signal transduction pathway linking initial perception of ethylene to gene expression.
