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

Abstract

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.

Combination of Transcriptomic, Proteomic, and Metabolomic Analysis Reveals the Ripening Mechanism of Banana Pulp

“…Our study suggested the possible role of MADS in banana pulp ripening, which was consistent with previous research [5]. Furthermore, the crosstalk between ethylene and other hormones including indole-3-acetic acid also influences fruit ripening [4]. Recently, the important roles of auxin in plant growth and development were well reviewed by Hagen [32].…”

“…The banana is a typical climacteric fruit and undergoes a rapid ripening process after harvest [3]. Pulp softening is the typical characteristic of banana ripening, which is essential for nutritional and sensorial quality of the fruit [4]. However, over-softening accelerates the senescence processes, which causes great economic losses.…”

Similarities and Differences of Photosynthesis Establishment Related mRNAs and Novel lncRNAs in Early Seedlings (Coleoptile/Cotyledon vs. True Leaf) of Rice and Arabidopsis

“…Leaf starch and sucrose allocation is a well-regulated process in carbohydrate metabolism. The amount of starch synthesis seems to be in harmony with the length of the dark period (Cordenunsi-Lysenko et al, 2019). Starch-sucrose distribution is affected by plant development and sink activity, as well as environmental factors such as light intensity, temperature and photoperiod length (Pilkington et al, 2015).…”

Optimization of a virus-induced gene silencing system and functional elucidation of MaBAM9b in postharvest banana fruits

“…Banana is an important and pleasantly avored tropical fruit that is popular with consumers worldwide [1]. As a typical starch conversion fruit, the starch content of banana fruit upon harvesting can reach 12-35% fresh weight (FW) [2]. Starch is degraded and converted to sucrose rapidly during the post-harvest banana fruit ripening process [3].…”

“…Starch is degraded and converted to sucrose rapidly during the post-harvest banana fruit ripening process [3]. The soluble sugars may reach up to 20% FW of the pulp in the ripe fruit, with sucrose accounting for approximately 80%, whereas glucose and fructose make up almost all the remaining 20% of the soluble sugars in equal proportions [2]. During banana fruit ripening process, the sucrose content varied from 12.2 to 411.8 mg g -1 FW, while the glucose and fructose contents varied from 2.1 to 100.5 mg g -1 FW and 1.5 to 103.8 mg g -1 FW, respectively (not published data).…”