Cross Talk Between Drought Stress and Developmental Senescence Pathways In Petunia

The postproduction shelf life and garden performance of ornamental plants is greatly reduced by flower and leaf senescence.  Developmental senescence occurs as plant organs age, but senescence and death can be accelerated by exposure to ethylene or abiotic and biotic stresses.  We recently used a proteomic approach to investigate protein profiles in senescing Petunia × hybrida corollas.  One of the senescence-specific proteins in corollas was identified as a putative ASR (abscisic acid, stress and ripening induced) protein.  A full length cDNA encoding the petunia ASR (PhASR4) was identified from a petunia EST collection.  PhASR4 shares 60% amino acid identity with the tomato ASR4.  PhASR4 transcripts were detected at basal levels in ‘Mitchell Diploid’ (MD) corollas on the day of flower opening (anthesis) and increased at 6 days after anthesis when the flowers were just showing visual symptoms of senescence.  PhASR4 had 2-fold lower transcript abundance at anthesis in ethylene insensitive transgenic petunia corollas (35S::etr1-1).  The increase in transcript abundance accompanying flower senescence in MD flowers was not detected in etr1-1 flowers. PhASR4 was also found to be very responsive to drought stress.  Petunias were exposed to drought stress by withholding water until plants were completely wilted.  Plants were then rewatered and this cycle was repeated three times.  PhASR4 transcripts increased as soil moisture content decreased.  After plants were rewatered, PhASR4 transcript levels decreased.  PhASR4s putative role in developmental and stress-induced senescence and its regulation by plant hormones will be discussed.