Unraveling Cuticle Formation, Structure, and Properties by Using Tomato Genetic Diversity

SlMYB72 interacts with SlTAGL1 to regulate the cuticle formation in tomato fruit

The cuticle is the first physical barrier covering the surface of tomatoes and plays an important role in multiple stress responses. But the molecular regulatory networks of cuticle formation are not fully understood. In this study, we found that SlMYB72 can interact with SlTAGL1 to regulate the formation of fruit cuticle in tomato. Downregulating the expression of SlMYB72 inhibits the formation of fruit cuticle, resulting in a reduced fruit cuticle thickness, accelerated postharvest water loss, and increased susceptibility to Botrytis cinerea. RNA sequencing analysis showed that downregulation of the SlMYB72 gene decreased the expression levels of genes related to fatty acid and cuticle metabolism. SlMYB72 regulates the cuticle formation by directly binding to the promoter of long-chain acyl-coA synthetases (SlLACS1) and medium-chain alkane hydroxylase (SlMAH1). Moreover, SlMYB72 interacts with SlTAGL1, which can enhance the transcriptional activation of SlMYB72 on the SlMAH1 promoter. Overall, our study expands our understanding of the regulation of cuticle formation by SlMYB72 and provides new insights into fruit shelf life extension via manipulation of cuticle content.

Cuticle development and the underlying transcriptome-metabolome associations during early seedling establishment

The plant cuticle is a complex extracellular lipid barrier that has multiple protective functions. This study investigated cuticle deposition by integrating metabolomics and transcriptomics data gathered from six different maize seedling organs of four genotypes, the inbred lines B73 and Mo17, and their reciprocal hybrids. These datasets captured the developmental transition of the seedling from heterotrophic skotomorphogenic growth to autotrophic photomorphogenic growth, a transition that is highly vulnerable to environmental stresses. Statistical interrogation of these data revealed that the predominant determinant of cuticle composition is seedling organ type, whereas the seedling genotype has a smaller effect on this phenotype. Gene-to-metabolite associations assessed by integrated statistical analyses identified three gene networks associated with the deposition of different elements of the cuticle: cuticular waxes; monomers of lipidized cell wall biopolymers, including cutin and suberin; and both of these elements. These gene networks reveal three metabolic programs that appear to support cuticle deposition, including processes of chloroplast biogenesis, lipid metabolism, and molecular regulation (e.g. transcription factors, post-translational regulators, and phytohormones). This study demonstrates the wider physiological metabolic context that can determine cuticle deposition and lays the groundwork for new targets for modulating the properties of this protective barrier.

La2O3 Nanoparticles Can Cause Cracking of Tomato Fruit through Genetic Reconstruction

La2O3 nanoparticles (NPs) have shown great potential in agriculture, but cracking of plant sensitive tissue could occur during application, resulting in a poor appearance, facilitating entry for insects and fungi, and increasing economic losses. Herein, exocarp cracking mechanisms of tomato (Solanum lycopersicum L.) fruit in response to La2O3 NPs were investigated. Tomato plants were exposed to La2O3 NPs (0-40 mg/L, 90 days) by a split-root system under greenhouse condition. La2O3 NPs with high concentrations (25 and 40 mg/L) increased the obvious cracking of the fruit exocarp by 20.0 and 22.7%, respectively. After exposure to 25 mg/L La2O3 NPs, decreased thickness of the cuticle and cell wall and lower wax crystallization patterns of tomato fruit exocarp were observed. Biomechanical properties (e.g., firmness and stiffness) of fruit exocarp were decreased by 34.7 and 25.9%, respectively. RNA-sequencing revealed that the thinner cuticle was caused by the downregulation of cuticle biosynthesis related genes; pectin remodeling, including the reduction in homogalacturonan (e.g., LOC101264880) and rhamnose (e.g., LOC101248505), was responsible for the thinner cell wall. Additionally, genes related to water and abscisic acid homeostasis were significantly upregulated, causing the increases of water and soluble solid content of fruit and elevated fruit inner pressure. Therefore, the thinner fruit cuticle and cell wall combined with the higher inner pressure caused fruit cracking. This study improves our understanding of nanomaterials on important agricultural crops, including the structural reconstruction of fruit exocarp contributing to NPs-induced cracking at the molecular level.

The role of cuticle in fruit shelf-life

Ensuring the availability of high-quality fresh fruits requires the development of strategies to maintain prolonged shelf-life. The plant cuticle is a modification of the outer epidermal cell wall and, as such, acts as a barrier with the environment. Understanding how the cuticle naturally changes during postharvest is crucial to address the potential effect of different storage conditions on the cuticle biophysical properties. The impact of different cuticle traits in fruit water loss, its relevance in several fruit-skin disorders, and its participation in postharvest decay caused by pathogens are discussed. Future challenges to study in vivo the physicochemical properties of the cuticle are also addressed.

Genome-wide identification, comprehensive characterization of transcription factors, cis-regulatory elements, protein homology, and protein interaction network of DREB gene family in Solanum lycopersicum

Tomato is a drought-sensitive crop which has high susceptibility to adverse climatic changes. Dehydration-responsive element-binding (DREB) are significant plant transcription factors that have a vital role in regulating plant abiotic stress tolerance by networking with DRE/CRT cis-regulatory elements in response to stresses. In this study, bioinformatics analysis was performed to conduct the genome-wide identification and characterization of DREB genes and promoter elements in Solanum lycopersicum. In genome-wide coverage, 58 SlDREB genes were discovered on 12 chromosomes that justified the criteria of the presence of AP2 domain as conserved motifs. Intron-exon organization and motif analysis showed consistency with phylogenetic analysis and confirmed the absence of the A3 class, thus dividing the SlDREB genes into five categories. Gene expansion was observed through tandem duplication and segmental duplication gene events in SlDREB genes. Ka/Ks values were calculated in ortholog pairs that indicated divergence time and occurrence of purification selection during the evolutionary period. Synteny analysis demonstrated that 32 out of 58 and 47 out of 58 SlDREB genes were orthologs to Arabidopsis and Solanum tuberosum, respectively. Subcellular localization predicted that SlDREB genes were present in the nucleus and performed primary functions in DNA binding to regulate the transcriptional processes according to gene ontology. Cis-acting regulatory element analysis revealed the presence of 103 motifs in 2.5-kbp upstream promoter sequences of 58 SlDREB genes. Five representative SlDREB proteins were selected from the resultant DREB subgroups for 3D protein modeling through the Phyre2 server. All models confirmed about 90% residues in the favorable region through Ramachandran plot analysis. Moreover, active catalytic sites and occurrence in disorder regions indicated the structural and functional flexibility of SlDREB proteins. Protein association networks through STRING software suggested the potential interactors that belong to different gene families and are involved in regulating similar functional and biological processes. Transcriptome data analysis has revealed that the SlDREB gene family is engaged in defense response against drought and heat stress conditions in tomato. Overall, this comprehensive research reveals the identification and characterization of SlDREB genes that provide potential knowledge for improving abiotic stress tolerance in tomato.

The cutin polymer matrix undergoes a fine architectural tuning from early tomato fruit development to ripening

The cuticle is a complex polymer matrix that protects all aerial organs of plants, fulfills multiple roles in plant-environment interactions, and is critical for plant development. These functions are associated with the structural features of cuticles, and the architectural modeling of cuticles during plant development is crucial for understanding their physical properties and biological functions. In this work, the in-depth architecture of the cutin polymer matrix during fruit development was investigated. Using cherry tomato fruit (Solanum lycopersicum) as a model from the beginning of the cell expansion phase to the red ripe stage, we designed an experimental scheme combining sample pretreatment, Raman mapping, multivariate data analyses, and biochemical analyses. These approaches revealed clear chemical areas with different contributions of cutin, polysaccharides, and phenolics within the cutin polymer matrix. Besides, we demonstrated that these areas are finely tuned during fruit development, including compositional and macromolecular rearrangements. The specific spatiotemporal accumulation of phenolic compounds (p-coumaric acid and flavonoids) suggests that they fulfill distinct functions during fruit development. In addition, we highlighted an unexpected dynamic remodeling of the cutin-embedded polysaccharides pectin, cellulose, and hemicellulose. Such structural tuning enables consistent adaption of the cutin-polysaccharide continuum and the functional performance of the fruit cuticle at the different developmental stages. This study provides insights into the plant cuticle architecture and in particular into the organization of the epidermal cell wall-cuticle.

Wood-Derived Vascular Patches Loaded With Rapamycin Inhibit Neointimal Hyperplasia

Background: Patches are commonly used to close blood vessels after vascular surgery. Most currently used materials are either prosthetics or animal-derived; although natural materials, such as a leaf, can be used as a patch, healing of these natural materials is not optimal; rhodamine and rapamycin have been used to show that coating patches with drugs allow drug delivery to inhibit neointimal hyperplasia that may improve patch healing. Wood is abundant, and its stiffness can be reduced with processing; however, whether wood can be used as a vascular patch is not established. We hypothesized that wood can be used as a vascular patch and thus may serve as a novel plant-based biocompatible material.

Method: Male Sprague–Dawley rats (aged 6–8 weeks) were used as an inferior vena cava (IVC) patch venoplasty model. After softening, wood patches coated with rhodamine and rapamycin were implanted into the rat subcutaneous tissue, the abdominal cavity, or the IVC. Samples were explanted on day 14 for analysis.

Result: Wood patches became soft after processing. Patches showed biocompatibility after implantation into the subcutaneous tissue or the abdominal cavity. After implantation into the IVC, the patches retained mechanical strength. There was a significantly thinner neointima in wood patches coated with rapamycin than control patches (146.7 ± 15.32 μm vs. 524.7 ± 26.81 μm; p = 0.0001). There were CD34 and nestin-positive cells throughout the patch, and neointimal endothelial cells were Eph-B4 and COUP-TFII-positive. There was a significantly smaller number of PCNA and α-actin dual-positive cells in the neointima (p = 0.0003), peri-patch area (p = 0.0198), and adventitia (p = 0.0004) in wood patches coated with rapamycin than control patches. Piezo1 was expressed in the neointima and peri-patch area, and there were decreased CD68 and piezo1 dual-positive cells in wood patches coated with rapamycin compared to control patches.

Conclusion: Wood can be used as a novel biomaterial that can be implanted as a vascular patch and also serve as a scaffold for drug delivery. Plant-derived materials may be an alternative to prosthetics or animal-based materials in vascular applications.

The SlSHN2 transcription factor contributes to cuticle formation and epidermal patterning in tomato fruit

Tomato (Solanum lycopersicum) is an established model for studying plant cuticle because of its thick cuticle covering and embedding the epidermal cells of the fruit. In this study, we screened an EMS mutant collection of the miniature tomato cultivar Micro-Tom for fruit cracking mutants and found a mutant displaying a glossy fruit phenotype. By using an established mapping-by-sequencing strategy, we identified the causal mutation in the SlSHN2 transcription factor that is specifically expressed in outer epidermis of growing fruit. The point mutation in the shn2 mutant introduces a K to N amino acid change in the highly conserved 'mm' domain of SHN proteins. The cuticle from shn2 fruit showed a ~ fivefold reduction in cutin while abundance and composition of waxes were barely affected. In addition to alterations in cuticle thickness and properties, epidermal patterning and polysaccharide composition of the cuticle were changed. RNAseq analysis further highlighted the altered expression of hundreds of genes in the fruit exocarp of shn2, including genes associated with cuticle and cell wall formation, hormone signaling and response, and transcriptional regulation. In conclusion, we showed that a point mutation in the transcriptional regulator SlSHN2 causes major changes in fruit cuticle formation and its coordination with epidermal patterning.