Systems biology applied to the study of papaya fruit ripening: the influence of ethylene / Biologia de sistemas aplicada ao estudo do amadurecimento de mamões: a influência do etileno

Fruit ripening is a biochemical process that results in flavor, odor, texture, and color suitable for human consumption, in addition to providing access to important nutrients. Although ripening promotes sensory and nutritional increases in fruits, there is also an increased susceptibility to physical damage, as is the case with papaya. These transformations occur due to changes in gene expression patterns at different stages of maturity, whose control and coordination result from the combined action of plant hormones, especially ethylene. As the action of this hormone in the regulation of gene expression is still elusive, this dissertation sought to address the global analysis of the transcriptome in an overview study of molecular processes involved in the ripening of ethylene-treated and non-treated papaya. Transcription factors related to ethylene synthesis and signaling had increased activity towards exogenous-ethylene treatment. Consequently, ethylene-induced enzymes had their coding genes differentially expressed, like genes related to the synthesis of carotenoids, linalool, and vitamins, which increase color, aroma, and antioxidant activity, respectively. Metabolic pathways related to the synthesis of sugars were suppressed while genes encoding the enzyme responsible for sucrose synthesis maintained a basal expression, showing that the accumulation of sugars occurs before the ripening process. The firmness of the peel and pulp of the fruits were strongly influenced by the treatment with ethylene and by the time of the experiment, suffering the action of numerous enzymes related to the degradation of the cell wall. The main enzyme responsible for softening the pulp was polygalacturonase, together with the activity of other pectinases and cellulases. In contrast to the need for the pre-climacteric action of pectate lyase and pectinesterase reported in other fleshy fruits, such as tomatoes and strawberries, papaya did not show a significant difference in their expression. The meta-analysis of several papaya ripening transcriptomes confirmed the expression profile observed in the previous RNA-seq, besides providing statistical enrichment to the biological narratives. Finally, the present study gathered a range of robust information on the gene regulation of the papaya ripening process, which opens possibilities for future approaches to transcriptomic analysis and validates the use of papaya as a model for such studies

O amadurecimento de frutos é um processo bioquímico que resulta em sabor, odor, textura e cor adequados para o consumo humano, além de propiciar o acesso a nutrientes importantes. Apesar do amadurecimento promover incrementos sensoriais e nutricionais nos frutos, ocorre também um aumento da suscetibilidade a danos físicos, como é o caso do mamão. Essas transformações ocorrem devido às alterações nos padrões de expressão gênica nos diferentes estádios de amadurecimento, cujo controle e coordenação decorrem da ação combinada de hormônios vegetais, principalmente do etileno. Como a ação deste hormônio na regulação da expressão gênica ainda é elusiva, a presente dissertação buscou abordar a análise global do transcriptoma em um amplo estudo dos processos moleculares envolvidos no amadurecimento de mamões tratados e não tratados com etileno. Os fatores de transcrição relacionados com a síntese e a sinalização do etileno tiveram sua atividade aumentada perante o tratamento exógeno com etileno. Consequentemente, as enzimas reguladas por esse hormônio tiveram seus genes de codificação expressos diferencialmente, como foi o caso de genes relacionados à síntese de carotenoides, linalool e vitaminas, que atuam no aumento da cor, aroma e atividade antioxidante, respectivamente. Vias metabólicas relacionadas com à síntese de açúcares foram reprimidas enquanto genes codificantes da enzima responsável pela síntese de sacarose mantiveram uma expressão basal, evidenciando que o acúmulo de açúcares ocorre antes do processo de amadurecimento. A firmeza da casca e da polpa dos frutos foram fortemente influenciadas pelo tratamento com etileno e pelo tempo de experimento, sofrendo ação de inúmeras enzimas relacionadas com a degradação da parede celular. A principal enzima responsável pelo amolecimento da polpa foi a poligalacturonase, em conjunto com a atividade de outras pectinases e celulases. Em contraste com a necessidade da ação pré-climatérica da pectato liase e da pectinesterase relatada em outras frutas carnosas, como tomates e morangos, o mamão não apresentou uma diferença significativa na expressão das mesmas. A meta-análise de diversos transcriptomas do amadurecimento do mamão reafirmaram o perfil de expressão observado no RNA-seq, além de prover enriquecimento estatístico às narrativas biológicas. Por fim, o presente estudo reuniu uma gama de informações robustas sobre a regulação gênica do processo de amadurecimento do mamão papaia, o que abrange a possibilidade para futuras abordagens de análise transcriptomica e valida o uso do mamão como modelo para tais estudos

The role of cell wall polysaccharides disassembly in Lasiodiplodia theobromae-induced disease occurrence and softening of fresh longan fruit.

Cell wall polysaccharides in fruits act a pivotal role in their resistance to fungal invasion. Lasiodiplodia theobromae (Pat.) Griff. & Maubl. is a primary pathogenic fungus causing the spoilage of fresh longan fruit. In this study, the influences of L. theobromae inoculation on the disassembly of cell wall polysaccharides in pericarp of fresh longans and its association with L. theobromae-induced disease and softening development were investigated. In contrast to the control, samples with L. theobromae infection showed more severe disease development, lower firmness, lower amounts of cell wall materials, covalent-soluble pectin, ionic-soluble pectin, cellulose and hemicellulose, whereas higher value of water-soluble pectin, higher activities of cell wall polysaccharide-disassembling enzymes (cellulase, ß-galactosidase, polygalacturonase and pectinesterase). These findings revealed that cell wall polysaccharides disassembly induced by enzymatic manipulation was an essential pathway for L. theobromae to infect harvested longans, and thus led to the disease occurrence and fruit softening.

A novel chitosan alleviates pulp breakdown of harvested longan fruit by suppressing disassembly of cell wall polysaccharides.

Longan pulp is an excellent source of polysaccharides and other nutrients that have many health benefits. However, longans is susceptible to pulp breakdown after harvest and loses its nutrition values. To solve this problem, this study aimed to study the effects of a novel chitosan, Kadozan, on pulp breakdown index, contents of pectin, cellulose and hemicelluloses, and activities of enzymes in longan pulp relating to disassembly of polysaccharides (XET, PE, PG, ß-Gal, and cellulase). The data illustrated that, compared to the control longans, chitosan-treated longans contained higher amounts of CWM, CSP, ISP, cellulose and hemicelluloses, but exhibited lower pulp breakdown index, lower activities of cell wall-disassembling enzymes, and contained lower WSP amount. These results suggested that Kadozan with a dilution of 1:500 (VKadozan: VKadozan + Water) could significantly decrease activities of disassembling-enzymes and depolymerization of polysaccharides in cell wall, and subsequently alleviate pulp breakdown and prolong storage-life of postharvest longans.

XTHs from Fragaria vesca: genomic structure and transcriptomic analysis in ripening fruit and other tissues.

BACKGROUND: Fragaria vesca or 'woodland strawberry' has emerged as an attractive model for the study of ripening of non-climacteric fruit. It has several advantages, such as its small genome and its diploidy. The recent availability of the complete sequence of its genome opens the possibility for further analysis and its use as a reference species. Fruit softening is a physiological event and involves many biochemical changes that take place at the final stages of fruit development; among them, the remodeling of cell walls by the action of a set of enzymes. Xyloglucan endotransglycosylase/hydrolase (XTH) is a cell wall-associated enzyme, which is encoded by a multigene family. Its action modifies the structure of xyloglucans, a diverse group of polysaccharides that crosslink with cellulose microfibrills, affecting therefore the functional structure of the cell wall. The aim of this work is to identify the XTH-encoding genes present in F. vesca and to determine its transcription level in ripening fruit. RESULTS: The search resulted in identification of 26 XTH-encoding genes named as FvXTHs. Genetic structure and phylogenetic analyses were performed allowing the classification of FvXTH genes into three phylogenetic groups: 17 in group I/II, 2 in group IIIA and 4 in group IIIB. Two sequences were included into the ancestral group. Through a comparative analysis, characteristic structural protein domains were found in FvXTH protein sequences. In complement, expression analyses of FvXTHs by qPCR were performed in fruit at different developmental and ripening stages, as well as, in other tissues. The results showed a diverse expression pattern of FvXTHs in several tissues, although most of them are highly expressed in roots. Their expression patterns are not related to their respective phylogenetic groups. In addition, most FvXTHs are expressed in ripe fruit, and interestingly, some of them (FvXTH 18 and 20, belonging to phylogenic group I/II, and FvXTH 25 and 26 to group IIIB) display an increasing expression pattern as the fruit ripens. CONCLUSION: A discrete group of FvXTHs (18, 20, 25 and 26) increases their expression during softening of F. vesca fruit, and could take part in cell wall remodeling required for softening in collaboration with other cell wall degrading enzymes.