Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/12/2010
Publication Date: 1/2/2011
Citation: Handa, A.K., Nambeesan, S., Mengiste, T., Laluk, K., Abuqamar, S., Mattoo, A.K. 2011. Polyamine spermidine is an upstream negator of ethylene-regulated pathogenesis of botrytis cinerea in tomato leaf. Acta Horticulturae. 914:109-112. Interpretive Summary: Genetically engineered tomato lines were developed by introducing a yeast gene called spermidine synthase (SpdSyn) in which the fruit shriveling and decay symptoms are delayed. One of the lines was engineered to have SpdSyn gene express equally well in the vegetative tissue (SpdSyn-leaf) and fruits. The SpdSyn-leaf line was found to have a longer vegetative growth than the wild type. To check if longer vegetative growth in the latter line in some way compromised on the response to pathogens, we tested the resistance of leaf tissue against different pathogens. One of the pathogens inoculated on the leaves was a necrotrophic fungus, called Botrytis cinerea, which is responsible for the grey mold disease. Surprisingly, the leaves of SpdSyn-leaf plants were found more susceptible to Botrytis infection than the leaves from wild type tomato. This susceptibility was reversed when the leaves were pretreated with ACC, a precursor of the plant hormone ethylene. Similarly, inhibitors of polyamine biosynthesis reversed the symptoms of Botrytis infection. These results unearth a new microbe-plant interaction showing that polyamine Spd and ethylene differentially regulate Botrytis pathogenesis of tomato. These findings are of interest to plant pathologists, plant biologists, horticulturists and molecular biologists.
Technical Abstract: Polyamines are biogenic polycationic compounds implicated in a number of processes including plant cell division, cell elongation, flowering, fruit set and development, fruit ripening, senescence and responses to abiotic stresses. Comparatively, little is known about their role in plant-microbe interactions. To address an involvement of polyamines in tomato-pathogen interactions, we developed transgenic tomato lines homozygous for the introduced yeast spermidine synthase (ySpdSyn) under the CaMV35S promoter, which accumulated higher levels of polyamine spermidine (Spd). These transgenic and wild type control lines were challenged with Botrytis cinerea. Transgenic tomato leaves were found to be more susceptible to B. cinerea compared to the wild type. During B. cinerea-leaf interactions in the transgenic lines, a significant decrease occurred in the transcript levels of genes involved in ethylene biosynthesis, such as 1-aminocyclopropane-l-carboxylate (ACC) synthase, and ethylene signaling. In the leaf from transgenic tomato lines, higher susceptibility to B. cinerea was reversed by exogenous application of ACC or difluoromethylornithine (DFMO), an inhibitor of polyamine biosynthesis. The transcript levels of defense genes regulated by salicylic acid or jasmonates were similar between the high Spd-transgenic leaves and the wild type. Collectively, these results demonstrate selective susceptibility of Spd-accumulating plants to necrotrophic B. cinerea pathogen, and suggest a role for both ethylene and polyamines in B. cinerea-tomato pathogenesis.