Metabolome and proteome of ethylene-treated papayas reveal different pathways to volatile compounds biosynthesis.

Papayas undergo fast postharvest changes triggered by the plant hormone ethylene. Some important pathways have been analyzed in limited studies (transcriptomics and targeted metabolomics); however, broad use of proteomics or untargeted metabolomics have not yet been used in papayas. In this study, two groups of green papayas (150 days after anthesis-physiological maturity for papayas) were treated with ethylene at different times (6 and 12 h) and their metabolic changes in fruit pulp were evaluated with untargeted metabolomics (general metabolites and volatile compounds) and proteomics. Polar metabolites exhibited distinct patterns, especially with regard to some amino and fatty acids during stimulated ripening. In particular, glutamate increased through a possible gamma aminobutyric acid (GABA) shunt and/or proteases activity. Moreover, the stimulated ripening altered the volatile compounds and the protein profiles. The results suggest that changes in membrane breakdown and the resulting oxidative processes could be responsible for volatile compound production, altering some sensorial qualities of papayas, such as pulp softening and the specific papaya linalool volatile compound increment. Thus, GABA levels could also be a strong biological marker for papaya development and ripening stages. This study applied two "omic" techniques that provided insight into how the plant hormone ethylene could influence papaya postharvest quality.

Metabolomic profiling reveals that natural biodiversity surrounding a banana crop may positively influence the nutritional/sensorial profile of ripe fruits.

This study is part of an extensive project that evaluated the effects of a natural ecosystem on a healthy banana crop and the quality of its fruit. In particular, the study examined the influence of the maintenance of natural biodiversity (Atlantic forest) near a conventional banana crop on the metabolic profiling of ripe banana fruits. Results revealed differences between ripe fruits harvested from plants near the natural forest (Near-NF) and fruits harvested in areas distant from the natural forest (Distant-NF). A total of 76 metabolites were identified in ripe banana fruits. Bananas harvested from Near-NF plot showed increased levels of γ-aminobutyric acid and reduced levels of putrescine compared with fruits from Distant-NF plot. Furthermore, fatty acids profile suggests that ripe fruits harvested from Near-NF plot had increased nutritional quality compared with fruits from Distant-NF plot. Multivariate statistical analysis revealed that these metabolites, which potentially influence the nutritional/sensorial quality of ripe fruits, also contributed to distinguishing fruits harvested from Near-NF and Distant-NF plots. Collectively, the results suggest that the natural biodiversity surrounding a crop area could benefit ripe banana nutritional/sensorial quality. The maintenance of natural forest fragments thus appears to be a promising tool for increasing the quality of fruit crops.

The Starch Is (Not) Just Another Brick in the Wall: The Primary Metabolism of Sugars During Banana Ripening.

The monocot banana fruit is one of the most important crops worldwide. As a typical climacteric fruit, the harvest of commercial bananas usually occurs when the fruit is physiologically mature but unripe. The universal treatment of green bananas with ethylene or ethylene-releasing compounds in order to accelerate and standardize the ripening of a bunch of bananas mimics natural maturation after increasing the exogenous production of ethylene. The trigger of autocatalytic ethylene production regulated by a dual positive feedback loop circuit derived from a NAC gene and three MADS genes results in metabolic processes that induce changes in the primary metabolism of bananas. These changes include pulp softening and sweetening which are sensorial attributes that determine banana postharvest quality. During fruit development, bananas accumulate large amounts of starch (between 15 and 35% w/w of their fresh weight, depending on the cultivar). Pulp softening and sweetening during banana ripening are attributed not only to changes in the activities of cell wall hydrolases but also to starch-to-sugar metabolism. Therefore, starch granule erosion and disassembling are key events that lead bananas to reach their optimal postharvest quality. The knowledge of the mechanisms that regulate sugar primary metabolism during banana ripening is fundamental to reduce postharvest losses and improve final product quality, though. Recent studies have shown that ethylene-mediated regulation of starch-degrading enzymes at transcriptional and translational levels is crucial for sugar metabolism in banana ripening. Furthermore, the crosstalk between ethylene and other hormones including indole-3-acetic acid and abscisic acid also influences primary sugar metabolism. In this review, we will describe the state-of-the-art sugar primary metabolism in bananas and discuss the recent findings that shed light on the understanding of the molecular mechanisms involved in the regulation of this metabolism during fruit ripening.

Two banana cultivars differ in composition of potentially immunomodulatory mannan and arabinogalactan.

Banana (Musa acuminata and M. acuminata x M. balbisiana) fruit cell walls are rich in mannans, homogalacturonans and xylogalacturonan, rhamnogalacturonan-I, and arabinogalactans, certain forms of which is considered to have immunomodulatory activity. The cultivars Nanicão and Thap Maeo represent two widely variants with respect to compositional differences in the forms of these polysaccharides. Nanicão has low amounts of mannan in the water-insoluble and water-soluble fraction. Both cultivars have high amounts of water-soluble arabinogalactan. These commelinoid monocots lack the (1→3),(1→4)-ß-d-glucans of grasses, but Thap Maeo has higher amounts of non-starch glucans associated with wild species than does Nanicão. High amount of callose was found in both cultivars. As immunomodulatory activity is associated with the fine structure and interaction of these polysaccharides, breeding programs to introgress disease resistance from wild species must account for these special structural features in retaining fruit quality and beneficial properties.