1a. Objectives (from AD-416):
The goal is to identify mechanisms by which polyamines enhance the accumulation of choline and N-transport amino acids in tomato fruit. Further, we will determine if increased production and quality attributes in tomato plants grown under leguminous cover crop (hairy vetch) involve polyamine-responsive component(s).
1b. Approach (from AD-416):
We will use transgenic technology to develop genotypes enriched in nutrients beneficial for human health. These genotypes will be analyzed for gene expression, particularly to elucidate mechanisms responding to higher polyamines. The interaction of methyl jasmonate with polyamines in regulating fruit metabolism will be analyzed in methyl jasmonate deficient transgenic tomato genotype. Influence of cover crop mulches on gene expression and metabolite profiles will be conducted on field grown transgenic and non-transgenic plants.
3. Progress Report:
Recently, ubiquitous biogenic polyamines, such as putrescine, spermidine and spermine, have emerged as significant growth regulators of both fruit quality and shelf life. To gain an insight into the role of polyamines and other hormones in fruit biology, a scientist at the ARS’s Sustainable Agricultural Systems Laboratory, Beltsville, Maryland in collaboration with researchers at the Purdue University and at CNR, Rome, Italy, have developed transgenic tomato lines that either accumulate polyamines (overexpression of S-adenosylmethionine decarboxylase), or are deficient in the synthesis of ethylene (antisense to ACC synthase) or the stress hormone methyl jasmonate (co-suppression of the key gene lipoxygenase, LOX). These transgenic lines are being used to test if and how the cellular metabolome is modulated in tomato lines that accumulate higher levels of lycopene and other micronutrients and those that have a longer shelf life or are disease-tolerant. Initial evidence shows alteration in the cellular metabolome in the different tomato lines mentioned above. The relevance of such shifts on accumulation of antioxidants or on the organoleptic characteristics of fruit are being evaluated.
1. A unique cluster of small heat shock protein genes in tandem with a set of small nucleolar RNA genes was identified on tomato chromosome 6. Elucidation of how genes are organized on a chromosome of a plant helps in determining their function as well as phylogenetic relationships and the evolution of species. A set of genes implicated in fruit ripening belongs to class I small heat shock proteins. We identified and sequenced an 8.3-kilobase genomic fragment harboring a unique cluster of three class I small heat shock protein genes in tandem with a set of small nucleolar RNA (snoRNA) genes. This 8.3-kilobase genomic fragment contains important elements that respond to plant hormones and extreme heat, cold and dehydration. The USDA-ARS, Beltsville scientist in collaboration with colleagues at the USDA-ARS’s Boyce Thompson Institute, Ithaca, demonstrated that this fragment was localized on the short arm of chromosome 6. The particular organization of the kinds of genes identified suggests this gene fragment to be an important site of networks that regulate not only tomato growth but also responses to abiotic and biotic stresses. This study is of paramount interest to geneticists, molecular biologists, horticulturists, evolutionary biologists and breeders.
2. Polyamines and ethylene differentially regulate Botrytis pathogenesis of tomato. Novel genetically engineered tomato lines, in which the fruit shriveling and decay symptoms are delayed, were developed by a Sustainable Agricultural Systems Laboratory scientist at Beltsville in collaboration with a Purdue University scientist. This tomato line was found to have longer vegetative growth than the wild type. The leaves of SpdSyn-leaf plants were found to be more susceptible to Botrytis infection than the wild type tomato. This susceptibility was reversed when the leaves were pretreated with ACC, a precursor of the plant hormone ethylene, or when inhibitors of polyamine biosynthesis were applied. These results unearthed a new microbe-plant interaction that is of interest to plant pathologists, plant biologists, horticulturists and molecular biologists.
3. Legume cover crops offer physiological advantages to crops other than those derived from inorganic N alone. Management of nitrogen (N) in farming practices is of global concern. Previously, N signaling pathways were found associated with hairy vetch grown tomatoes suggesting that N in hairy vetch residue may be the basis for the associated phenotypes. Scientists at the Sustainable Agricultural Systems Laboratory, Beltsville, have now shown that crops can distinguish between an organic and inorganic source of nitrogen (N). Further, it was found that tomato responses at the whole plant (yield), leaf (photosynthesis), and molecular (gene expression) levels to the legume hairy vetch are a result of cues by molecules other than just N. These findings are important to horticulturists, plant biologists, ecologists and molecular biotechnologists.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.