Location: Sustainable Agricultural Systems Laboratory
2022 Annual Report
Objectives
Objective 1: Identify metabolic pathways and nutrient molecules that are impacted by cold, heat, and drought stress in tomato. [NP301, C3, PS3A]
Objective 2: Determine the mineral and nutritional metabolite composition of field-grown legume and some non-legume cover crops, and determine how their constituents modify tomato stress tolerance – cold, heat, drought, and yield – using existing transgenic or mutant tomato lines. [NP301, C3, PS3A; C1, PS1A]
Objective 3: Determine how plant responses to cold, heat, and drought are modified at the transcript level in tomato by the hyperaccumulation of polyamines and/or the reduction of the stress hormones, ethylene and methyl jasmonate. [NP301, C3, PS3A]
Approach
Utilize previously developed genetically engineered tomato genotypes - two that have fruit ripening-specific accumulation of polyamines spermidine and spermine (Spd-Spm), other two that constitutively-express spermidine, one that is 50% reduced in fruit-ripening hormone ethylene (Eth-def), another that is deficient in the stress hormone methyl jasmonate (JAS-def), a cross between Eth-def and Spd-Spm, and a cross between JAS-def and Spd-Spm – and test them for tolerance against abiotic stresses such as drought, heat, and cold, and yield. Analyses for water use efficiency (WUE), gene medleys, nutrient content, yield, fruit quantity and quality, metabolic pathways, and gene networks will be defined. In addition, field-grown legume and non-legume cover crops will be analyzed for their levels of metabolites and biomolecules just before flowering time to provide a lead into their utilization for imparting field-based resistance against abiotic stresses in field-grown tomato genotypes.
Progress Report
Tomato is one of the major vegetable crops worldwide regarding consumption and production volume with an annual yield surpassing 182 million tons. Ripe tomato fruit is a source of dietary micronutrients, vitamins, and antioxidants for daily human consumption. Tomato is also an established model system, especially for developing novel information on ripening and senescence of fleshy fruits. In addition to unraveling mechanisms that increase fruit yield and longer shelf life, consumer recognition of fruits as sources of health-promoting nutrients for a healthier life has intensified research on tomato. Therefore, our research efforts have been directed toward understanding the genetics of the tomato ripening process, the role of plant hormones, particularly ethylene, and deciphering signal transduction pathways. Tomato is also vulnerable to environmental extremes, including diverse abiotic and biotic stressors, which impact its growth, yield and nutritional quality. Our goals include identification of genetic and biochemical determinants of normal biology of tomato and unraveling the stress pathways so that novel tomato germplasm that can withstand abiotic stresses and minimize yield losses can be developed. Our research studies are also focused on the combinatorial role(s) of plant hormones in enhancing nutrient load and stress tolerance in tomato. The salient features of hormone biology are important in understanding cross talks between hormones as well as for developing stress-resistant germplasm. Plant hormones studied include ethylene, jasmonic acid and a group of low molecular weight organic cations called polyamines, namely, putrescine (PUT), spermidine (SPD), spermine (SPM), and T-spermine (theo-SPM). These four polyamines have been implicated in regulating plant growth, and inhibiting senescence and stress responses of plants.
Although a plethora of genes and proteins have been implicated in tomato fruit ripening, developing fruits to have longer shelf life without compromising the nutrient content has yet to be achieved.
We have also undertaken a study to understand the novel dynamics involved in aquatic plants which are not sessile and therefore are a good model to ascertain how these plants survive and regulate extreme environmental stresses.
For Objective 1 we studied the impact of drought and salinity on plant growth and development, vis a vis polyamines, that have been implicated in ameliorating the detrimental effects of drought and salinity. The independent impact of these two abiotic stresses on polyamine (PA) biosynthesis, catabolism, and homeostasis, as well as on their transcript abundance in tomato leaves was studied. Total levels of PUT, SPD, and SPM increased up to 72 h during drought and up to 48 h during salinity stress before their precipitable drop thereafter. These data demonstrated that tomato plants survive drought and salinity stress for up to 3 and 2 days, respectively. Independent multivariant analyses of drought and salinity stress kinetic data separately showed a closer association with levels of free, conjugated, and bound forms of SPD and SPM, but not with free or bound PUT. However, combined multivariant analyses showed a closer association of free SPD, conjugated SPD, and bound SPD with both stresses; SPD-bound and SPM-conjugated with drought; and free SPM and conjugated PUT with salinity stress, respectively. PA biosynthesis genes, ARG1, SPDS1, and SAMDc3 segregated with drought and SPDS2 with salinity stress. PA catabolic genes CuAO4-like and PAO4 were associated with drought and salinity stresses, respectively, suggesting differential involvement of PA biosynthesis and catabolic genes in drought and salinity stresses. Pearson correlation indicated mostly positive correlations between the levels of free, conjugated, and bound forms of PUT, SPD, and SPM under drought and salinity stress. Levels of different PA forms had a two-fold higher negative correlation during drought as compared to salinity stress (66 vs. 32) and with transcript levels of PA biosynthesis and catabolic genes. Transcripts of light-harvesting chlorophyll a/b-binding genes were generally positively associated with different forms of PAs but negatively associated with carbon flow genes. Most of the PA biosynthesis genes were coordinately regulated under both stresses. Collectively, these results indicated that PAs are distinctly regulated under drought and salinity stress with different but specific homologs of PA biosynthesis and catabolic genes contributing to the accumulation of free, conjugated, and bound forms of PAs. The research was also extended to a small grain crop maize for its growth enhancement with cover crops and currently transcriptome and metabolome data is being analyzed along with writing of one manuscript based on maize results.
To develop an understanding of how PA pathway evolution helped migration of aquatic plants to land, we used an aquatic plant model, duckweed (Spirodela polyrhiza). Specifically, we used duckweed to investigate the role of the PA pathway in stress tolerance and mitigation. Analysis of PA biosynthetic pathway genes in duckweed revealed the presence of prokaryotic as well as land plant-type ADC pathway genes but the absence of ODC encoding genes. Differential gene expression and transcript abundance of PA biosynthetic genes was found to be modulated by exogenous methyl jasmonate, salinity, and acidic pH. Two manuscripts describing this work were written and published.
For Objective 2 we utilized RNA sequencing to identify novel metabolic pathways modulated in corn and tomato in response to the cover crop hairy vetch in comparison to non-vetch-grown corn and tomato plants. RNA sequencing data analysis revealed that phytohormones resulting from cover crop management hold the key for cover crop-based benefits to corn and tomato. Also, we used nontargeted metabolomic analysis to detect endogenous phytohormone metabolites, profiling approximately 30 hormones and their catabolites. Preliminary data analysis revealed that phytohormones and their pathway metabolite abundances were based on growth stage. Cover crop modulation of corn growth and phytohormone abundance was coordinated at transcriptome and gene expression levels and thereby cover crops modify the phenotype of whole plants.
For Objective 3 we demonstrated that metabolic pathways and plant hormones including PA experience a shift in transcriptional regulation and response to abiotic stress under drought, heat, salt, and cold conditions. Drought is an adverse climatic condition that affects yield, nutritional quantity, and biomass production in tomato and other crops. Our data revealed that PA synthesis is upregulated under long-term drought conditions while ethylene/ 1-aminocyclopropane 1-carboxylic acid (ACC) transcripts are downregulated which suggests that PA are positive regulators that prevent losses due to drought. A comprehensive approach is needed to determine the role(s) PA and phytohormones (ethylene/ACC) play in drought conditions during 3 to 4 weeks of long-term drought tolerance. Our datasets on gene expression analysis suggest that a negative relationship exists between ethylene and PA synthesis during short-term drought. Subjecting higher PA transgenic tomato genotypes to drought revealed that such plants are tolerant to drought for 4 weeks with high tomato yield and root/shoot biomass. Further, subjecting ethylene-deficient germplasm to similar conditions revealed that they too had drought tolerance.
Accomplishments
1. Higher polyamine levels in transgenic tomato genotypes provide tolerance to drought along with higher tomato yield. ARS scientists in Beltsville, Maryland, identified and characterized transgenic tomato plants that have tolerance against drought plus higher yield. Drought causes loss of produce as well as lower nutritional value in commodities such as tomato. Tomato yield in high polyamine producing lines under drought conditions was either sustained at a similar level or higher in comparison to the control tomato genotype. Ethylene-deficient germplasm subjected to similar conditions also was found to have a similar level of drought tolerance with high polyamine lines due to lower ethylene hormone levels during drought stress conditions. Our results represent both strategies: either increasing polyamine levels in plants or reducing ethylene levels will provide drought tolerance in tomato. Now scientists and breeders can design and develop new drought-resistant tomato germplasm. This information is useful to molecular biologists and plant breeders developing heat-stress resistant tomatoes.
Review Publications
Upadhyay, Rakesh K, Shao, J.Y., Mattoo, A.K. 2021. Genomic analysis of the polyamine biosynthesis pathway in duckweed Spirodela polyrhiza L.: presence of the arginine decarboxylase pathway, absence of the ornithine decarboxylase pathway, and response to abiotic stresses. Planta. 254:108. https://doi.org/10.1007/s00425-021-03755-5.
Upadhyay, R.K., Fatima, T., Handa, A.K., Mattoo, A.K. 2021. Differential association of free, conjugated, and bound forms of polyamines and transcript abundance of their biosynthetic and catabolic genes during drought/salinity stress in tomato (Solanum lycopersicum L.) leaves. Frontiers in Plant Science. 12:743568. https://doi.org/10.3389/fpls.2021.743568.
Gajewska, J., Floryszak-Wieczorek, J., Sobieszczuk-Nowicka, E., Mattoo, A.K., Plociennik, A., Arasimowicz-Jelonek, M. 2022. Fungal and oomycete pathogens and heavy metals: an inglorious couple in the environment. IMA Fungus. https://doi.org/10.1186/s43008-022-00092-4.
Mattoo, A.K., Dwivedi, S.I., Dutt, S., Singh, B., Garg, M., Ortiz, R. 2022. Anthocyanin-rich vegetables for human consumption - focus on potato, sweetpotato and tomato. International Journal of Molecular Sciences. 23:5. https://doi.org/10.3390/ijms23052634.
Goyal, R.K., Mattoo, A.K., Schmidt, A.M. 2021. Rhizobial-host interactions and symbiotic nitrogen fixation in legume crops toward agriculture sustainability. Frontiers in Microbiology. https://doi.org/10.3389/fmicb.2021.669404.
Dwivedi, S.I., Mattoo, A.K., Garg, M., Dutt, S., Singh, B., Ortiz, R. 2022. Food crops, anthocyanins, and non-communicable human diseases. Crop Science. https://doi.org/10.3389/fsufs.2022.867897.
