Submitted to: Plant Physiology
Publication Type: Review article
Publication Acceptance Date: 11/21/2011
Publication Date: 11/29/2011
Citation: Nambeesan, S., Abuqamar, S., Mattoo, A.K., Laluk, K., Mickelbart, M.V., Ferruzzi, M.G., Mengiste, T., Handa, A.K. 2011. Polyamines attenuate ethylene-mediated defense responses to abrogate resistance to Botrytis cinerea in tomato. Plant Physiology. 158:1034-1045. Interpretive Summary: We are developing genetically engineered tomato lines with higher nutritional quality and longer shelf life. It is important to ascertain if such novel genotypes become more susceptible to pathogens, particularly when the plants live longer. One of the genetically-enhanced lines, developed in collaboration with scientists at Purdue University, accumulated a biogenic amine, called spermidine, in the vegetative tissue and fruits. This transgenic line had a longer vegetative growth than the wild type. We tested the resistance of leaf tissue from this line 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. We found that the leaves of the spermidine-accumulating plants were 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, and upon treatment of leaves with inhibitors of polyamine biosynthesis. Moreover, it was found that the spermidine-mediated pathology was associated with suppression of genes involved in ethylene biosynthesis and action. These results unearth hitherto unknown microbe-plant interaction showing that polyamine spermidine and ethylene differentially regulate Botrytis pathogenesis of tomato. These findings are of interest to plant pathologists, plant biologists, horticulturists and molecular biologists.
Technical Abstract: Transgenic tomato (Solanum lycopersicum) lines over-expressing yeast spermidine synthase (ySpdSyn), an enzyme involved in polyamine (PA) biosynthesis, were developed. These transgenic lines accumulate higher levels of spermidine (Spd) than the wild type plants and were examined for responses to the fungal necrotrophs Botrytis cinerea and Alternaria solani, bacterial pathogen Pseudomonas syringae pv. tomato DC3000, and larvae of the chewing insect tobacco hornworm (Manduca sexta). The Spd-accumulating transgenic tomato lines were found more susceptible to B. cinerea than the wild type plants; however, responses to A. solani, P. syringae, or M. sexta were similar to the wild type plants. Exogenous application of ethylene precursors, S-adenosylmethionine (SAM) and 1-aminocyclopropane-1-carboxylic acid (ACC), or PA biosynthesis inhibitors reversed the response of the transgenic plants to B. cinerea. The higher susceptibility of the ySpdSyn transgenic tomato to B. cinerea was associated with down-regulation of gene transcripts involved in ethylene biosynthesis and signaling.