Abnormal behavior of chilling injury in postharvest papaya fruit is associated with sugar metabolism

Fine mapping and identification of ERF transcription factor ERF017 as a candidate gene for cold tolerance in pumpkin

KEY MESSAGE

Two major QTLs for cold tolerance in pumpkin were localised, and CmoERF017 was identified as a key candidate gene within these QTLs via RNA-seq. Functional analysis revealed that CmoERF017 was a positive regulator of pumpkin in response to low-temperature stress. Low temperature is a key environmental factor that affects the protected cultivation of cucumber (Cucumis sativus L.) in winter, and the cold tolerance of cucumber/pumpkin-grafted seedlings depends on the rootstock. Pumpkin (Cucurbita spp.) has a well-developed root system, high resistance and wide adaptation, commonly used as rootstock for cucumber to improve the cold tolerance of grafted seedlings. This study used two high-generation inbred lines of Cucurbita moschata with significant differences in cold tolerance. We identified key candidate genes within the major cold tolerance QTL of rootstocks using QTL-seq and RNA-seq and investigated the function and molecular mechanisms of these genes in response to low-temperature stress. Results showed that QTL-seq located two cold tolerance QTLs, qCII-1 and qCII-2, while RNA-seq located 28 differentially expressed genes within these QTLs. CmoERF017 was finally identified as a key candidate gene. Functional validation results indicated that CmoERF017 is a positive regulator of pumpkin in response to low-temperature stress and affected root ABA synthesis and signalling by directly regulating the expression of SDR7 and ABI5. This study identified a key gene for low-temperature stress tolerance in rootstock pumpkin and clarified its role in the molecular mechanism of hormone-mediated plant cold tolerance. The study findings enrich the theoretical understanding of low-temperature stress tolerance in pumpkin and are valuable for the selection and breeding of cold-tolerant varieties of pumpkin used for rootstocks.

Regulation of Embden-Meyerhof-Parnas (EMP) Pathway and Tricarboxylic Acid (TCA) Cycle Concerning Aberrant Chilling Injury Behavior in Postharvest Papaya (Carica papaya L.)

Postharvest abnormal chilling injury (CI) behavior in papaya (Carica papaya L.) fruit is a rare phenomenon that may be associated with respiratory metabolism. This study thus aimed to investigate the impacts of storage temperatures (1 and 6 °C) on the respiratory metabolism of postharvest papaya and its impact on CI development. Results demonstrated that 1 °C storage reduced the activities of hexokinase (HK), phosphofructokinase (PFK), pyruvate kinase (PK), citrate synthase (CS), and α-ketoglutarate dehydrogenase (α-KGDH) and regulated the expression of corresponding enzymes in the Embden-Meyerhof-Parnas (EMP) pathway and tricarboxylic acid (TCA) cycle compared with 6 °C storage, resulting in a lower respiration rate of the EMP-TCA pathway and mitigating the development of CI. Meanwhile, lower contents of nicotinamide adenine dinucleotide (hydrogen) (NAD(H)) were observed in papaya fruit stored at 1 °C. Notably, papaya fruit stored at 1 °C maintained higher activity and transcriptional levels of SDH and IDH during the whole storage period. These findings suggest that 1 °C storage reduced the respiration rate of the EMP-TCA pathway by reducing the expression level and activity of related enzymes, which is conducive to the reduction of respiration substrate consumption and finally alleviating the occurrence of CI.

Genome-wide identification and expression reveal the involvement of the FCS-like zinc finger (FLZ) gene family in Gossypium hirsutum at low temperature

FCS-like zinc finger (FLZ) is a plant-specific gene family that plays an important regulatory role in plant growth and development and its response to stress. However, studies on the characteristics and functions of cotton FLZ family genes are still lacking. This study systematically identified members of the cotton FLZ gene family based on cotton genome data. The cotton FLZ family genes were systematically analyzed by bioinformatics, and their expression patterns in different tissues and under low-temperature stress were analyzed by transcriptome and qRT-PCR. The G. hirsutum genome contains 56 FLZ genes distributed on 20 chromosomes, and most of them are located in the nucleus. According to the number and evolution analysis of FLZ family genes, FLZ family genes can be divided into five subgroups in cotton. The G. hirsutum FLZ gene has a wide range of tissue expression types, among which the expression is generally higher in roots, stems, leaves, receptacles and calyx. Through promoter analysis, it was found that it contained the most cis-acting elements related to methyl jasmonate (MeJA) and abscisic acid (ABA). Combined with the promoter and qRT-PCR results, it was speculated that GhFLZ11, GhFLZ25, GhFLZ44 and GhFLZ55 were involved in the response of cotton to low-temperature stress. Taken together, our findings suggest an important role for the FLZ gene family in the cotton response to cold stress. This study provides an important theoretical basis for further research on the function of the FLZ gene family and the molecular mechanism of the cotton response to low temperature.

Dissecting postharvest chilling injury through biotechnology

Paradoxically, refrigerating many fruits and vegetables destroys their quality, and may even accelerate their spoilage. This phenomenon, known as postharvest chilling injury (PCI), affects produce from tropical and subtropical regions and leads to economic and postharvest loss and waste. Low temperatures are used to pause the physiological processes associated with senescence, but upon rewarming, these processes may resume at an accelerated rate. Chilling-injured produce may be discarded for not meeting consumer expectations or may prematurely deteriorate. In this review, we describe progress made in identifying the cellular and molecular processes underlying PCI, and point to advances in biotechnological approaches for ameliorating symptoms. Further, we identify the gaps in knowledge that must be bridged to develop effective solutions to PCI.

Effect of alginate-based coating charged with hydroxyapatite and quercetin on colour, firmness, sugars and volatile compounds of fresh cut papaya during cold storage

Active alginate-based coatings with quercetin glycoside and complexes of hydroxyapatite/quercetin-glycoside were used to study the shelf life of fresh cut papaya stored at 6 °C. Hydroxyapatite was used as a carrier for the release of the bioactive compound. The parameters considered affecting the quality of the fruit during storage were weight loss, color, texture, sugars and volatile compounds. Active coatings with hydroxyapatite and quercetin glycoside proved a higher capacity to slow down the degradation phenomena studied, showing less weight loss, a lower reduction in glucose and fructose, as well as better firmness, than the other samples after 14 days of cold storage. Benzyl isothiocyanate, the characteristic odor compound of papaya fruit, ranged from approximately 10.0 μg/kg in fresh cut fruit to approximately 7.50 μg/kg in samples coated by alginate with hydroxyapatite/quercetin and 3.6 μg/kg in the fresh cut papaya without coating after 14 days of cold storage. The trials also indicated greater effectiveness of alginate coatings alone and with quercetin-glucoside in preserving the color of freshly cut papaya.