RESUMEN

BACKGROUND: Watermelon seeds are a powerhouse of value-added traits such as proteins, free amino acids, vitamins, and essential minerals, offering a paleo-friendly dietary option. Despite the availability of substantial genetic variation, there is no sufficient information on the natural variation in seed-bound amino acids or proteins across the watermelon germplasm. This study aimed to analyze the natural variation in watermelon seed amino acids and total protein and explore underpinning genetic loci by genome-wide association study (GWAS). METHODS: The study evaluated the distribution of seed-bound free amino acids and total protein in 211 watermelon accessions of Citrullus spp, including 154 of Citrullus lanatus, 54 of Citrullus mucosospermus (egusi) and three of Citrullus amarus. We used the GWAS approach to associate seed phenotypes with 11,456 single nucleotide polymorphisms (SNPs) generated by genotyping-by-sequencing (GBS). RESULTS: Our results demonstrate a significant natural variation in different free amino acids and total protein content across accessions and geographic regions. The accessions with high protein content and proportion of essential amino acids warrant its use for value-added benefits in the food and feed industries via biofortification. The GWAS analysis identified 188 SNPs coinciding with 167 candidate genes associated with watermelon seed-bound amino acids and total protein. Clustering of SNPs associated with individual amino acids found by principal component analysis was independent of the speciation or cultivar groups and was not selected during the domestication of sweet watermelon. The identified candidate genes were involved in metabolic pathways associated with amino acid metabolism, such as Argininosuccinate synthase, explaining 7% of the variation in arginine content, which validate their functional relevance and potential for marker-assisted analysis selection. This study provides a platform for exploring potential gene loci involved in seed-bound amino acids metabolism, useful in genetic analysis and development of watermelon varieties with superior seed nutritional values.

RESUMEN

Watermelon (Citrullus lanatus L.) is a widely popular vegetable fruit crop for human consumption. Soil salinity is among the most critical problems for agricultural production, food security, and sustainability. The transcriptomic and the primary molecular mechanisms that underlie the salt-induced responses in watermelon plants remain uncertain. In this study, the photosynthetic efficiency of photosystem II, free amino acids, and transcriptome profiles of watermelon seedlings exposed to short-term salt stress (300 mM NaCl) were analyzed to identify the genes and pathways associated with response to salt stress. We observed that the maximal photochemical efficiency of photosystem II decreased in salt-stressed plants. Most free amino acids in the leaves of salt-stressed plants increased many folds, while the percent distribution of glutamate and glutamine relative to the amino acid pool decreased. Transcriptome analysis revealed 7622 differentially expressed genes (DEGs) under salt stress, of which 4055 were up-regulated. The GO analysis showed that the molecular function term "transcription factor (TF) activity" was enriched. The assembled transcriptome demonstrated up-regulation of 240 and down-regulation of 194 differentially expressed TFs, of which the members of ERF, WRKY, NAC bHLH, and MYB-related families were over-represented. The functional significance of DEGs associated with endocytosis, amino acid metabolism, nitrogen metabolism, photosynthesis, and hormonal pathways in response to salt stress are discussed. The findings from this study provide novel insights into the salt tolerance mechanism in watermelon.

Asunto(s)

Citrullus/efectos de los fármacos , Regulación de la Expresión Génica de las Plantas , Proteínas de Plantas/genética , Tolerancia a la Sal/genética , Plantones/efectos de los fármacos , Cloruro de Sodio/farmacología , Transcriptoma , Aminoácidos/metabolismo , Citrullus/genética , Citrullus/metabolismo , Perfilación de la Expresión Génica , Ontología de Genes , Anotación de Secuencia Molecular , Fotosíntesis/efectos de los fármacos , Fotosíntesis/genética , Complejo de Proteína del Fotosistema II/efectos de los fármacos , Complejo de Proteína del Fotosistema II/genética , Complejo de Proteína del Fotosistema II/metabolismo , Hojas de la Planta/efectos de los fármacos , Hojas de la Planta/genética , Hojas de la Planta/metabolismo , Proteínas de Plantas/clasificación , Proteínas de Plantas/metabolismo , Raíces de Plantas/efectos de los fármacos , Raíces de Plantas/genética , Raíces de Plantas/metabolismo , Salinidad , Plantones/genética , Plantones/metabolismo , Estrés Fisiológico

RESUMEN

The type-B authentic response regulators (ARR-Bs) function as positive regulators of cytokinin signal transduction and play important roles in abiotic stress resistance and plant development. However, little of ARR-B family is known in tomato. In this study, we performed a comprehensive analysis of ARR-B family factors in tomato. In total, 12 genes encoding ARR-B transcription factors (named as SlARR-B1-SlARR-B12) were identified from tomato. We analyzed the structures, chromosome locations, phylogeny, protein motifs, and expression profiles of these SlARR-B genes. Gene structure analysis showed that 5-12 exons and 4-11 introns existed in the SlARR-B genes. These SlARR-B genes were asymmetrically distributed on eight chromosomes in tomato. Phylogenetic tree of SlARR-B genes from tomato and other plant species revealed that SlARR-B genes were classified into 6 subfamilies. SlARR-B proteins had typical conserved domains, including Motif 1 and Motif 2. The investigation of the expression profiles of SlARR-B genes in all the examined tissues demonstrated that these genes were differentially expressed, including roots, stems, leaves, flowers, and fruits at developmental stages. Notably, the expression of SlARR-B11 and SlARR-B12 exhibited high expression levels in flowers. Each gene was induced by at least one of different phytohormones (SA, IAA, ABA, IBA, 6-BA, JA, GA, and ETH) and four abiotic stress treatments (heat, drought, salt, and cold). This study sets a good foundation for further characterization of the SlARR-B transcription factors in plant development and abiotic stress responses of tomato.

Asunto(s)

Familia de Multigenes , Solanum lycopersicum/genética , Estrés Fisiológico , Factores de Transcripción/genética , Secuencia Conservada , Regulación del Desarrollo de la Expresión Génica , Regulación de la Expresión Génica de las Plantas , Genes de Plantas , Filogenia , Reguladores del Crecimiento de las Plantas

RESUMEN

A non-protein amino acid, citrulline, is a compatible solute involved in the maintenance of cellular osmolarity during abiotic stresses. Despite its significance, a coherent model indicating the role of citrulline during stress conditions has not yet emerged. We have used watermelon, naturally rich in citrulline, as a model to understand its accumulation during drought stress and nitrogen perturbation using transcriptomic and metabolomic analysis. Experiments were performed in the semi-controlled environment, and open field to study the accumulation of drought-induced citrulline in the vegetative tissues of watermelon by monitoring the stress treatments using physiological measurements. The amino acid profiling of leaves and stems in response to drought stress showed up to a 38 and 16-fold increase in citrulline content, respectively. Correlation between amino acids indicated a concomitant activation of a metabolic pathway that included citrulline, its precursor (ornithine), and catabolic product (arginine). Consistent with its accumulation, the gene expression analysis and RNA-Sequencing confirmed activation of citrulline biosynthesis-related genes - Ornithine carbamoyl-transferase (OTC), N-acetylornithine deacetylase (AOD) and Carbamoyl phosphate synthases (CPS), and down-regulation of catabolic genes; Arginosuccinate lyase (ASL) and Arginosuccinate synthases (ASS) in drought-stressed leaf tissues. Based on the relative abundance in the nitrogen-depleted vegetative tissues and down-regulation of genes involved in citrulline biosynthesis, we also demonstrated that the nitrogen status of the plant regulates citrulline. Taken together, these data provide further insights into the metabolic and molecular mechanisms underlying the amino acid metabolism under environmental stress and the significance of non-protein amino acid citrulline in plants.