Transcriptome and Metabolome Analyses Provide Insights into the Watercore Disorder on “Akibae” Pear Fruit

Abstract

Watercore is a physiological disorder that commonly occurs in sand pear cultivars. The typical symptom of watercore tissue is transparency, and it is often accompanied by browning, breakdown and a bitter taste during fruit ripening. To better understand the molecular mechanisms of watercore affecting fruit quality, this study performed transcriptome and metabolome analyses on watercore pulp from “Akibae” fruit 125 days after flowering. The present study found that the “Akibae” pear watercore pulp contained higher sorbitol and sucrose than healthy fruit. Moreover, the structure of the cell wall was destroyed, and the content of pectin, cellulose and hemicellulose was significantly decreased. In addition, the content of ethanol and acetaldehyde was significantly increased, and the content of polyphenol was significantly decreased. Watercore induced up-regulated expression levels of sorbitol synthesis-related (sorbitol-6-phosphate dehydrogenase, S6PDH) and sucrose synthesis-related genes (sucrose synthesis, SS), whereas it inhibited the expression of sorbitol decomposition-related genes (sorbitol dehydrogenase, SDH) and sorbitol transport genes (sorbitol transporter, SOT). Watercore also strongly induced increased expression levels of cell wall-degrading enzymes (polygalactosidase, PG; ellulase, CX; pectin methylesterase, PME), as well as ethanol synthesis-related (alcohol dehydrogenase, ADH), acetaldehyde synthesis-related (pyruvate decarboxylase, PDC) and polyphenol decomposition-related genes (polyphenol oxidase, PPO). Moreover, the genes that are involved in ethylene (1-aminocyclopropane- 1-carboxylate oxidase, ACO; 1-aminocyclopropane- 1-carboxylate synthase, ACS) and abscisic acid (short-chain alcohol dehydrogenase, SDR; aldehyde oxidase, AAO) synthesis were significantly up-regulated. In addition, the bitter tasting amino acids, alkaloids and polyphenols were significantly increased in watercore tissue. Above all, these findings suggested that the metabolic disorder of sorbitol and sucrose can lead to an increase in plant hormones (abscisic acid and ethylene) and anaerobic respiration, resulting in aggravated fruit rot and the formation of bitter substances.

Residue Analysis and the Effect of Preharvest Forchlorfenuron (CPPU) Application on On-Tree Quality Maintenance of Ripe Fruit in “Feizixiao” Litchi (Litchi chinensis Sonn.)

“…Accumulation of alcohol was also reported in ripe mandarins (Hijaz et al, 2020). The development of watercore associated with fruit ripening in pear was found to be related to the occurrence of anaerobic respiration (Liu et al, 2021). Our study provided the first-hand evidence that CPPU significantly inhibits the accumulation of alcohol and acetic acid in overripe fruit, indicating that cytokinin prevents the occurrence of anaerobic respiration in litchi aril.…”

Watercore in Apple Landraces (Malus domestica Borkh.) as a quality indicator

“…As a result, watercore information should be considered in germplasm evaluations to detect cultivar potential. Following to Beaudry (2014) and Liu et al (2021), vitrescence gives to the apple a marble appearance, a crunchy texture, a delicate aroma, and an intense sweetness, which might be interesting in terms of differentiated quality. The efforts to promote local products adapted to regional environmental conditions also impulse rural development within the European Rural Development and the Sustainable Development Goals (SDGs) of the 2030 Agenda.…”

“…Although watercore has been studied in apples, this characteristic has also been identified in peach [Prunus persica (L.) Stokes] (Yamane et al, 2020), pear (Pyrus spp.) (Liu et al, 2021) and mangosteen (Garcinia mangostana L.) (Matra et al, 2019).…”

“…Sorbitol is polyhydric sugar alcohol synthetized from glucose by hydrogenation. This liquid fills the intercellular spaces, which are normally occupied by air (Beaudry, 2014;Liu et al, 2021). Vitrification is currently considered a defect in fruit crops, alleging that a deficiency of calcium in the soil might be the main cause (Calvo and Candan, 2013), being problems in storage one of the most negative consequences (Saquet, 2020).…”

Watercore Pear Fruit Respiration Changed and Accumulated γ-Aminobutyric Acid (GABA) in Response to Inner Hypoxia Stress

“…The cause of higher sorbitol accumulation is attributed to lower sorbitol transporter expression in watercore affected tissue [ 3 ]. Instead of transporting sorbitol into fruit storage parenchyma, it accumulates in intercellular spaces, and thus decreases intercellular space volume, which we speculate it can lead to hypoxia stress and ultimately, changing the internal flavor [ 4 , 5 ]. Plant adaptation to hypoxia is quiescence strategy.…”