Tissue specific analysis reveals a differential organization and regulation of both ethylene biosynthesis and E8 during climacteric ripening of tomato

Background: Solanum lycopersicum or tomato is extensively studied with respect to the ethylene metabolism during climacteric ripening, focusing almost exclusively on fruit pericarp. In this work the ethylene biosynthesis pathway was examined in all major tomato fruit tissues: pericarp, septa, columella, placenta, locular gel and seeds. The tissue specific ethylene production rate was measured throughout fruit development, climacteric ripening and postharvest storage. All ethylene intermediate metabolites (1-aminocyclopropane-1-carboxylic acid (ACC), malonyl-ACC (MACC) and S-adenosyl-L-methionine (SAM)) and enzyme activities (ACC-oxidase (ACO) and ACC-synthase (ACS)) were assessed. Results: All tissues showed a similar climacteric pattern in ethylene productions, but with a different amplitude. Profound differences were found between tissue types at the metabolic and enzymatic level. The pericarp tissue produced the highest amount of ethylene, but showed only a low ACC content and limited ACS activity, while the locular gel accumulated a lot of ACC, MACC and SAM and showed only limited ACO and ACS activity. Central tissues (septa, columella and placenta) showed a strong accumulation of ACC and MACC. These differences indicate that the ethylene biosynthesis pathway is organized and regulated in a tissue specific way. The possible role of inter- and intra-tissue transport is discussed to explain these discrepancies. Furthermore, the antagonistic relation between ACO and E8, an ethylene biosynthesis inhibiting protein, was shown to be tissue specific and developmentally regulated. In addition, ethylene inhibition by E8 is not achieved by a direct interaction between ACO and E8, as previously suggested in literature. Conclusions: The Ethylene biosynthesis pathway and E8 show a tissue specific and developmental differentiation throughout tomato fruit development and ripening

Deregulation of apoplastic polyamine oxidase affects development and salt response of tobacco plants

Polyamine (PA) homeostasis is associated with plant development, growth and responses to biotic/abiotic stresses. Apoplastic PA oxidase (PAO) catalyzes the oxidation of PAs contributing to cellular homeostasis of reactive oxygen species (ROS) and PAs. In tobacco, PAs decrease with plant age, while apoplastic PAO activity increases. Our previous results with young transgenic tobacco plants with enhanced/reduced apoplastic PAO activity (S-ZmPAO/AS-ZmPAO, respectively) established the importance of apoplastic PAO in controlling tolerance to short-term salt stress. However, it remains unclear if the apoplastic PAO pathway is important for salt tolerance at later stages of plant development. In this work, we examined whether apoplastic PAO controls also plant development and tolerance of adult plants during long-term salt stress. The AS-ZmPAO plants contained higher Ca2+ during salt stress, showing also reduced chlorophyll content index (CCI), leaf area and biomass but taller phenotype compared to the wild-type plants during salt. On the contrary, the S-ZmPAO had more leaves with slightly greater size compared to the AS-ZmPAO and higher antioxidant genes/enzyme activities. Accumulation of proline in the roots was evident at prolonged stress and correlated negatively with PAO deregulation as did the transcripts of genes mediating ethylene biosynthesis. In contrast to the strong effect of apoplastic PAO to salt tolerance in young plants described previously, the effect it exerts at later stages of development is rather moderate. However, the different phenotypes observed in plants deregulating PAO reinforce the view that apoplastic PAO exerts multifaceted roles on plant growth and stress responses. Our data suggest that deregulation of the apoplastic PAO can be further examined as a potential approach to breed plants with enhanced/reduced tolerance to abiotic stress with minimal associated trade-offs. © 2017 Elsevier Gmb

A comprehensive RNA-Seq-based gene expression atlas of the summer squash (Cucurbita pepo) provides insights into fruit morphology and ripening mechanisms

Background: Summer squash (Cucurbita pepo: Cucurbitaceae) are a popular horticultural crop for which there is insufficient genomic and transcriptomic information. Gene expression atlases are crucial for the identification of genes expressed in different tissues at various plant developmental stages. Here, we present the first comprehensive gene expression atlas for a summer squash cultivar, including transcripts obtained from seeds, shoots, leaf stem, young and developed leaves, male and female flowers, fruits of seven developmental stages, as well as primary and lateral roots. Results: In total, 27,868 genes and 2352 novel transcripts were annotated from these 16 tissues, with over 18,000 genes common to all tissue groups. Of these, 3812 were identified as housekeeping genes, half of which assigned to known gene ontologies. Flowers, seeds, and young fruits had the largest number of specific genes, whilst intermediate-age fruits the fewest. There also were genes that were differentially expressed in the various tissues, the male flower being the tissue with the most differentially expressed genes in pair-wise comparisons with the remaining tissues, and the leaf stem the least. The largest expression change during fruit development was early on, from female flower to fruit two days after pollination. A weighted correlation network analysis performed on the global gene expression dataset assigned 25,413 genes to 24 coexpression groups, and some of these groups exhibited strong tissue specificity. Conclusions: These findings enrich our understanding about the transcriptomic events associated with summer squash development and ripening. This comprehensive gene expression atlas is expected not only to provide a global view of gene expression patterns in all major tissues in C. pepo but to also serve as a valuable resource for functional genomics and gene discovery in Cucurbitaceae

A metabolome and transcriptome survey to tap the dynamics of fruit prolonged shelf-life and improved quality within Greek tomato germplasm

IntroductionTomato is a high economic value crop worldwide with recognized nutritional properties and diverse postharvest potential. Nowadays, there is an emerging awareness about the exploitation and utilization of underutilized traditional germplasm in modern breeding programs. In this context, the existing diversity among Greek accessions in terms of their postharvest life and nutritional value remains largely unexplored.MethodsHerein, a detailed evaluation of 130 tomato Greek accessions for postharvest and nutritional characteristics was performed, using metabolomics and transcriptomics, leading to the selection of accessions with these interesting traits. ResultsThe results showed remarkable differences among tomato Greek accessions for overall ripening parameters (color, firmness) and weight loss. On the basis of their postharvest performance, a balance between short shelf life (SSL) and long shelf life (LSL) accessions was revealed. Metabolome analysis performed on 14 selected accessions with contrasting shelf-life potential identified a total of 206 phytonutrients and volatile compounds. In turn, transcriptome analysis in fruits from the best SSL and the best LSL accessions revealed remarkable differences in the expression profiles of transcripts involved in key metabolic pathways related to fruit quality and postharvest potential. DiscussionThe pathways towards cell wall synthesis, polyamine synthesis, ABA catabolism, and steroidal alkaloids synthesis were mostly induced in the LSL accession, whereas those related to ethylene biosynthesis, cell wall degradation, isoprenoids, phenylpropanoids, ascorbic acid and aroma (TomloxC) were stimulated in the SSL accession. Overall, these data would provide valuable insights into the molecular mechanism towards enhancing shelf-life and improving flavor and aroma of modern tomato cultivars

Whole genome scanning of a Mediterranean basin hotspot collection provide new insights into olive tree biodiversity and biology

Olive tree (Olea europaea L. subsp. europaea var. europaea) is one of the most important species of the Mediterranean region and one of the most ancient species domesticated. The availability of whole genome assemblies and annotations of olive tree cultivars and oleaster (O. europaea subsp. europaea var. sylvestris) has contributed to a better understanding of genetic and genomic differences between olive tree cultivars. However, compared to other plant species there is still a lack of genomic resources for olive tree popula-tions that span the entire Mediterranean region. In the present study we developed the most complete genomic variation map and the most comprehensive catalog/resource of molecular variation to date for 89 olive tree genotypes originating from the entire Mediterranean basin, revealing the genetic diversity of this commercially significant crop tree and explaining the divergence/similarity among different variants. Addi-tionally, the monumental ancient tree ‘Throuba Naxos’ was studied to characterize the potential origin or routes of olive tree domestication. Several candidate genes known to be associated with key agronomic traits, including olive oil quality and fruit yield, were uncovered by a selective sweep scan to be under selection pressure on all olive tree chromosomes. To further exploit the genomic and phenotypic resources obtained from the current work, genome-wide association analyses were performed for 23 morphological and two agronomic traits. Significant associations were detected for eight traits that provide valuable candidates for fruit tree breeding and for deeper understanding of olive tree biology.info:eu-repo/semantics/publishedVersio

Whole genome scanning of a Mediterranean basin hotspot collection provides new insights into olive tree biodiversity and biology

Olive tree (Olea europaea L. subsp. europaea var. europaea) is one of the most important species of the Mediterranean region and one of the most ancient species domesticated. The availability of whole genome assemblies and annotations of olive tree cultivars and oleaster (O. europaea subsp. europaea var. sylvestris) has contributed to a better understanding of genetic and genomic differences between olive tree cultivars. However, compared to other plant species there is still a lack of genomic resources for olive tree populations that span the entire Mediterranean region. In the present study we developed the most complete genomic variation map and the most comprehensive catalog/resource of molecular variation to date for 89 olive tree genotypes originating from the entire Mediterranean basin, revealing the genetic diversity of this commercially significant crop tree and explaining the divergence/similarity among different variants. Additionally, the monumental ancient tree ‘Throuba Naxos’ was studied to characterize the potential origin or routes of olive tree domestication. Several candidate genes known to be associated with key agronomic traits, including olive oil quality and fruit yield, were uncovered by a selective sweep scan to be under selection pressure on all olive tree chromosomes. To further exploit the genomic and phenotypic resources obtained from the current work, genome-wide association analyses were performed for 23 morphological and two agronomic traits. Significant associations were detected for eight traits that provide valuable candidates for fruit tree breeding and for deeper understanding of olive tree biology.This research was financed by Greek Public Investments Program (PIP) of General Secretariat for Research & Technology (GSRT), under the Emblematic Action ‘The Olive Road’ (project code:2018ΣE01300000). Sebastián Ramos-Onsins is supported by the grant PID2020-119255GB-I00 (MICINN, Spain) and the CERCA Programme/Generalitat de Catalunya and acknowledges financial support from the Spanish Ministry of Economy and Competitiveness, through the Severo Ochoa Programme for Centres of Excellence in R&D 2016–2019 and 2020–2023 (SEV-2015-0533, CEX2019-000917) and the European Regional Development Fund (ERDF).The publication of the article in OA mode was financially supported by HEAL-Link.With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917).Peer reviewe

Genetic Control of Ascorbic Acid Biosynthesis and Recycling in Horticultural Crops

Ascorbic acid (AsA) is an essential compound present in almost all living organisms that has important functions in several aspects of plant growth and development, hormone signaling, as well as stress defense networks. In recent years, the genetic regulation of AsA metabolic pathways has received much attention due to its beneficial role in human diet. Despite the great variability within species, genotypes, tissues and developmental stages, AsA accumulation is considered to be controlled by the fine orchestration of net biosynthesis, recycling, degradation/oxidation, and/or intercellular and intracellular transport. To date, several structural genes from the AsA metabolic pathways and transcription factors are considered to significantly affect AsA in plant tissues, either at the level of activity, transcription or translation via feedback inhibition. Yet, all the emerging studies support the notion that the steps proceeding through GDP-L-galactose phosphorylase and to a lesser extent through GDP-D-mannose-3,5-epimerase are control points in governing AsA pool size in several species. In this mini review, we discuss the current consensus of the genetic regulation of AsA biosynthesis and recycling, with a focus on horticultural crops. The aspects of AsA degradation and transport are not discussed herein. Novel insights of how this multifaceted trait is regulated are critical to prioritize candidate genes for follow-up studies toward improving the nutritional value of fruits and vegetables

Regulation of fruit vitamin C metabolism

L-Ascorbic acid (AsA), or vitamin C, is an abundant low molecular dietary antioxidant compound that exerts a protective role against chronic diseases and disorders in humans. Genetic control of AsA concentrations in fruits can involve biosynthetic, recycling and transport mechanisms, as well as being linked to changes in whole fruit metabolism and/or plant growth. The aim of this work was to understand the genetics underlying the control of vitamin C metabolism in fruits. Two major approaches have been employed using two different fruit crops tomato and apple. Both species have medium AsA levels, but the significant variation among different cultivars (particularly in apple) clearly indicates that there is potential for improvement of this trait. In the first phase of this work, extensive biochemical analyses, as well as 14C-labelled and non-labelled substrate feeding experiments were carried out in various tissues and fruit ripening stages in two tomato cultivars. Results confirm that the L-galactose pathway is the main AsA biosynthetic route in tomato fruits, but substrates from alternative pathways can also be converted to AsA in fruits at specific developmental stages and genotypes. Overall, both biosynthetic capacity and the turnover rate of the AsA pool decline throughout ripening. However, the two tomato cultivars (AsA-rich Santorini and AsA-poor Ailsa Craig ) exhibited different profiles of AsA accumulation during ripening, but a characteristic peak in AsA-totAsA concentrations at the breaker stage. Differences in the activity of AsA recycling enzymes (particularly of MDHAR) helped explain the variations in fruit AsA concentrations of the two cultivars. In addition, expression profiles of an orthologue of GDP-L-galactose phosphorylase (SlGGP1), and two gene copies of monodehydroascorbate reductase (SlMDHAR1 and SlMDHAR3) were all closely associated with changes in AsA concentrations throughout ripening. Among these candidate genes, the expression of SlGGP1 was closely related with high AsA concentrations at red ripe fruits. To investigate the role of ethylene, two mutants inhibited in their ethylene responses (Never-ripe and ripening-inhibitor) were also studied. Results clearly indicate a key role of ethylene receptors in the control of fruit AsA pool that should be further investigated. In parallel with the tomato work, a combination of molecular, genetic and genomic approaches (QTL mapping, NGS, SNP discovery, gene expression and allelic association studies) were used to help identify key genes regulating fruit AsA concentrations in apple tissues. Stable AsA-QTLs over two or three years of measurements were mapped in LGs 10, 11, and 17. Candidate gene mapping demonstrated that the three paralogues of MdGGP are key regulators of AsA and totAsA concentrations in mature apple. Further, allelic variations in the transcript sequences of MdGGP1 (LG 11) and MdGGP3 (LG 10) arecloselylinked to fruit totAsA concentrations both within the Telamon x Braeburn mapping population and across a selection of commercial cultivars. Results from gene expression studies (qPCR) confirm that the expression of MdGGP1 and MdGGP3, as well as of a paralogue of dehydroascorbate reductase (MdDHAR3-3), are all strongly associated with fruit AsA concentrations in a selection of high- and low-vitamin C cultivars. These SNP-based markers are thus potentially excellent candidate for use within breeding programs to screen for progeny with increased AsA concentrations. At last, MdDHAR3 was found to have a key role in regulating the redox state of the AsA pool in apple fruits, and increased flesh DHA concentrations are associated with susceptibility to flesh browning. The separation of fruit into green and red side is beneficial for the better understanding of fruit AsA regulation, as highlighted by the improvement of AsA-QTL size and properties. The combined results in tomato and apple allow us to suggest that GGP has a central role in regulating fruit AsA levels which is broadly applicable at different fruit species. In terms of applied research, the identification of novel genes/alleles linked to high fruit AsA concentrations in apple can have immediate applications within fruit breeding programs via marker assisted breeding and screening.<w:latentstyles  <  <w:latentstyles="" semihidden="false" priority="0" locked="false"  status: publishe

Vitamins

Fruits and vegetables are the main source of health promoting phytonutrients, including vitamins, dietary fibers and phytochemicals. Vitamins are key bioactive compounds with strong antioxidant potential including both water-soluble (vitamins B and C) and lipid-soluble (vitamins A, E and K) compounds, and are thought to limit the risk of several chronic diseases such as cancers and cardio-vascular diseases. This chapter review recent advances in the understanding of the multiple roles of vitamins, as well as their major genetic regulatory pathways within plant kingdom. Further, it discusses vitamin occurrence and diversity in different plant tissues, organelles, and horticultural species, as well as throughout fruit development and at postharvest