Poster: Hormones

Abs # 580: High levels of polyamines in transgenic tomato fruit affect ethylene biosynthesis and its signal transduction pathway during ripening

Presenter:	Mattoo, Autar K, mattooa@ba.ars.usda.gov
Authors	Mattoo,  Autar K (A)   Neelam, Anil  (A)   Goyal, Ravinder  (B)   Solomos, Theophanes  (B)   Handa, Avtar K (C)
Affiliations:	(A): United States Department Agriculture (B): University of Maryland (C): Purdue University

Polyamines are ubiquitous in nature and have been implicated as growth regulators in plants. Pharmacological effects of polyamines include anti-senescence in vegetative tissues and delayed ripening in fruits. To study their in vivo role in tomato fruit ripening, transgenic tomato lines were developed that accumulate high levels of polyamines. This was achieved by introducing into tomato a yeast S-adenosylmethionine decarboxylase (SAMdc) gene coupled to a fruit specific promoter E8. S-adenosylmethionine is a common substrate that feeds into polyamine and ethylene biosynthetic pathways. Stable transgenic lines were shown to accumulate markedly high levels of polyamines, spermidine and spermine, in fruit as it ripened. Analysis of these transgenic fruit also revealed an increase in ethylene evolution in the order of 2-3 fold compared to non-transgenic fruit. Ripening of fruit on the vine in these plants was delayed in spite of the production of high levels of ethylene. To study the significance of this relationship between polyamines and ethylene during fruit ripening, key genes in the ethylene biosynthesis and signal transduction pathways were considered for study. ACC synthase transcripts in the transgenic fruits accumulated to higher levels, which is consistent with higher ethylene production rates. Likewise, northern analysis of RNA expression for the tomato receptor ETR3 at different stages of fruit ripening indicated a change in gene expression. These data suggest that polyamines modulate ethylene signaling at transcriptional level in the transgenic tomato fruit. We are investigating this probable cross talk between growth promoting polyamines and pro-ripening ethylene in tomato fruit.