A Multilevel Study of Melon Fruit Reticulation Provides Insight into Skin Ligno-Suberization Hallmarks

Abstract

The skin of fleshy fruit is typically covered by a thick cuticle. Some fruit species develop different forms of layers directly above their skin. Reticulation, for example, is a specialized suberin-based coating that ornaments some commercially important melon (Cucumis melo) fruit and is an important quality trait. Despite its importance, the structural, molecular, and biochemical features associated with reticulation are not fully understood. Here, we performed a multilevel investigation of structural attributes, chemical composition, and gene expression profiles on a set of reticulated and smooth skin melons. High-resolution microscopy, surface profiling, and histochemical staining assays show that reticulation comprises cells with heavily suberized walls accumulating large amounts of typical suberin monomers, as well as lignified cells localized underneath the specialized suberized cell layer. Reticulated skin was characterized by induced expression of biosynthetic genes acting in the core phenylpropanoid, suberin, lignin, and lignan pathways. Transcripts of genes associated with lipid polymer assembly, cell wall organization, and loosening were highly enriched in reticulated skin tissue. These signatures were exclusive to reticulated structures and absent in both the smooth surfaces observed in between reticulated regions and in the skin of smooth fruit. Our data provide important insights into the molecular and metabolic bases of reticulation and its tight association with skin ligno-suberization during melon fruit development. Moreover, these insights are likely to contribute to melon breeding programs aimed at improving postharvest qualities associated with fleshy fruit surface layers.

Russeting in ‘Apple’ Mango: Triggers and Mechanisms

“…The number of phellem layers in these stacks increased continuously. Similar observations were made in Malus apple, pear, and melons [ 15 , 19 , 21 ]. However, the maximum rate of increase in russet was reached later in developing ‘Apple’ mango compared with Malus apple or pear [ 15 , 21 ], where early fruit development is considered the most susceptible phase [ 22 ].…”

“…Russet in ‘Apple’ mango is similar to russet phenomena in other fruitcrop species, such as Malus apple [ 15 , 16 ], pear [ 17 ], citrus [ 18 ], grape [ 8 ], and melon [ 19 ]. This conclusion is based on the following arguments: (1) the appearance of the disorder in ‘Apple’ mango with rough brownish irregular patches surrounded by interconnected light brownish cracks is identical to that previously described for Malus apple [ 7 ].…”

“…This conclusion is based on the following arguments: (1) the appearance of the disorder in ‘Apple’ mango with rough brownish irregular patches surrounded by interconnected light brownish cracks is identical to that previously described for Malus apple [ 7 ]. (2) Cross-sections of the skin of ‘Apple’ mango identified stacks of suberised cells typical for a phellem produced by a phellogen as found in potatoes [ 20 ], Malus apple [ 3 , 13 ], reticulated melon [ 19 ], and grape [ 8 ]. The periderm of ‘Apple’ mango was stained with fluorol yellow, such as that of Malus apple [ 3 ].…”

Modified Atmosphere and Humidity Film Reduces Browning Susceptibility of Oriental Melon Suture Tissue during Cold Storage

“…Oleic acid was the major fatty acid on yellow peel (4.8% of total wax components), whereas stearic acid was the major fatty acid on white suture (7.4% of total wax components). This result was consistent with a recent study on smooth surface melon, such as honeydew [31]. A correlation between the epicuticular wax and water content loss were reported for several fruits, including mulberries and peppers [32,33].…”

Comparative Metabolomics and Molecular Phylogenetics of Melon (Cucumis melo, Cucurbitaceae) Biodiversity

“…Surprisingly, two mineral elements were in the top 20 molecular features highlighted by the RF analysis. Among the six compounds highlighted in peel, glycerol may be related with the fruit surface, such as cuticular waxes [53] or suberization [54]. Galactinol and raffinose linked classification to the raffinose family and to oligosaccharides metabolism in the peel (Table S4).…”