Influence of the Position of Mango Fruit on the Tree (Mangifera indica L. CV. ‘Zibda’) on Chilling Sensitivity and Antioxidant Enzyme Activity

Mango fruits sourced from tropical yields have had a high commercial comeback from being viewed as susceptible to chilling injury under long storage durations. When the fruits are exposed to cold storage, this results in physiological changes due to the side effects of the storage on the fruits, expanding the rates of loss during the period between harvest and marketing. It is difficult to harvest mangoes as the fruits show varying maturities and are located in different positions on the trees. The purpose of this study was to test the idea that fruits’ location on the tree influences how the fruit behaves during cold storage. During two seasons (2019–2020), the impact of on-tree fruit location, i.e., sunny side (SUN; fruit exposed to the sun for most of the day), shade (SHA; fruit grown on the shady side of trees), and inside the canopy (INS; fruit grown inside the tree canopy), on the chilling sensitivity and the activities of antioxidant enzymes of ‘Zibda’ mangos stored at a low temperature (4 ± 1 °C) for 35 days was determined. In contrast to SHA and SUN mangos, INS fruits were shown to be progressively tolerant to low storage temperatures. These fruits also showed the highest activities of ascorbate peroxidase (APX), peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD). In addition, the contents of O2− and H2O2 decreased in INS fruit during storage. Consequently, the cell membrane compartments were maintained, showing low accumulation of both malondialdehyde (MDA) and the protein carbonyl group (PCG) during storage. These results indicate that the fruit positions can also be considered at the time of harvesting for the classification of fruits before cold storage. This classification can also be added to the mango trading protocol to minimize the loss of economic returns by chilling injury.

Genetically-determined variations in photosynthesis indicate roles for specific fatty acid species in chilling responses

Using a population of recombinant inbred lines (RILs) cowpea (Vigna unguiculata. L. Walp), we tested for co-linkages between lipid contents and chilling responses of photosynthesis. Under low temperature conditions (19°C/13°C, day/night), we observed co-linkages between quantitative trait loci (QTL) intervals for photosynthetic light reactions and specific fatty acids, most strikingly, the thylakoid-specific fatty acid 16:1 found exclusively in phosphatidylglycerol (PG 16:1t). By contrast, we did not observe co-associations with bulk polyunsaturated fatty acids or high-melting-point-PG (sum of PG 16:0, PG 18:0 PG 16:1t) previously thought to be involved in chilling sensitivity. These results suggest that in cowpea, chilling sensitivity is modulated by specific lipid interactions rather than bulk properties. We were able to recapitulate the predicted impact of PG 16:1t levels on photosynthetic responses at low temperature using mutants and transgenic Arabidopsis lines. Because PG 16:1t synthesis requires the activity of peroxiredoxin-Q, which is activated by HO and known to be involved in redox signaling, we hypothesize that the accumulation of PG 16:1t occurs as a result of upstream effects on photosynthesis that alter redox status and production of reactive oxygen species.

Jasmonic acid and ERF family genes are involved in chilling sensitivity and seed browning of pepper fruit after harvest

Pepper (Capsicum annuum L.) fruit is sensitive to temperatures below 10 °C, which severely diminish fruit quality during cold chain distribution. Seed browning was a major chilling symptom in 36 genotypes of C. annuum fruit screened after storage at 2 °C for 3 weeks. Among them, pepper fruits of chilling-insensitive ‘UZB-GJG-1999–51’ and -sensitive ‘C00562’ were treated at 2 °C for 0 or 24 h, respectively. Analyses of integrated transcriptome-metabolome and relative gene expression in seeds obtained from the two genotypes were conducted to identify key factors involved in the seed browning induced by chilling. The relative contents of branched-chain amino acids such as leucine, isoleucine, and valine were significantly increased after chilling. Transcriptome identification showed 3,140 differentially expressed genes (log twofold change > 1.0 and FDR-corrected p value < 0.05) affected by chilling between the two genotypes. Particularly, genes related to jasmonic acid synthesis and signaling were differentially expressed. A regulatory network of jasmonic acid synthesis and signaling, and regulation of ERF family genes might contribute to chilling response in pepper fruit. The results of this study may help facilitate further studies to develop chilling-insensitive peppers and could be a basis for improving postharvest fruit quality.

Co-regulation role of endogenous hormones and transcriptomics profiling under cold stress in Tetrastigma hemsleyanum

Background: Tetrastigma hemsleyanum Diels et Gilg is a valuable medicinal herb, Chilling sensitivity is the dominant environmental factor limiting the artificial domestication of the plant. Hormone-related gene regulation and hormone signaling pathways in response to cold stress in T. hemsleyanum remain unknown. Results: Some key genes involved in hormones biosynthesis, such as ZEP and NCED genes of ABA biosynthesis, GA2ox, GA3ox, and GA20ox genes of GA biosynthesis, ACO genes of ET biosynthesis pathway were screened to be crucial in cold response. Consistently, the response of ABA and ABA/GA1+3 to cold stress was prior to that of GA1+3, ZR, ABA/IAA, and ABA/ZR. The increasing changes in ABA/GA1+3 turned to a steep decline with the extension of stress time, which might be one factor contributing to cold-sensitivity of T. hemsleyanum under prolonged stress. The cold tolerance of T. hemsleyanum would be enhanced by ABA but repressed by GA3 when each phytohormone was applied alone. The ABA-mediated promotion and GA-mediated repression of cold tolerance could both be attenuated by the co-application of the two phytohormones within 6h. When the biosynthesis of endogenous ABA and GA were inhibited by FLU and PAC, respectively, the effects of GA and ABA treatment were reversed partially. Conclusions: In summary, we presented the first study of global expression patterns of hormone-regulated transcripts in T. hemsleyanum. This study suggested that GA and ABA could work antagonistically to balance the responses to cold in T. hemsleyanum. PAC, a GA biogenesis inhibitor, as well as exogenous ABA, might be potential plant growth regulators that can promote cold tolerance of T. hemsleyanum. The study also provided valuable hints in revealing a new theoretical basis and potential candidate genes that govern cold tolerance of T. hemsleyanum.

Co-regulation role of endogenous hormones and transcriptomics profiling under cold stress in Tetrastigma hemsleyanum

Background: Tetrastigma hemsleyanum Diels et Gilg is a valuable medicinally herb, Chilling sensitivity is the dominant environmental factor limiting the artificial domestication of the plants. Hormone-related gene regulation and hormone signaling pathways in response to cold stress in T. hemsleyanum remain unknown.Results: Some key genes involved in hormones biosynthesis, such as ZEP and NCED genes of ABA biosynthesis, GA2ox, GA3ox, and GA20ox genes of GA biosynthesis, ACO genes of ET biosynthesis were screened to be crucial in cold response. Consistently, the response of ABA and ABA/GA1+3 to cold stress was prior to that of GA1+3, ZR, ABA/IAA, and ABA/ZR. The increasing changes in ABA/GA1+3 turned to a steep decline with the extension of stress time, which might be one factor contributing to cold-sensitivity of T. hemsleyanum under prolonged stress. The cold tolerance of T. hemsleyanum would be enhanced by endogenous ABA but repressed by GA3 when each phytohormone was applied alone. The ABA-mediated promotion and GA-mediated repression of cold tolerance could both be attenuated by the co-application of the two phytohormones within 6h. When the biosynthesis of endogenous ABA and GA were inhibited by FLU and PAC, respectively, the effects of GA and ABA treatment were reversed partially.Conclusions: In summary, we present the first study of global expression patterns of hormone-regulated transcripts in T. hemsleyanum. This study suggested that GA and ABA work antagonistically to balance the responses to cold in T. hemsleyanum. PAC, a GA biogenesis inhibitor, as well as exogenous ABA, might be potential plant growth regulators that can promote cold tolerance of T. hemsleyanum. The study also provided valuable hints in revealing a new theoretical basis and potential candidate genes that govern cold tolerance of T. hemsleyanum.

Genetic Architecture of Chilling Tolerance in Sorghum Dissected with a Nested Association Mapping Population

Dissecting the genetic architecture of stress tolerance in crops is critical to understand and improve adaptation. In temperate climates, early planting of chilling-tolerant varieties could provide longer growing seasons and drought escape, but chilling tolerance (<15°) is generally lacking in tropical-origin crops. Here we developed a nested association mapping (NAM) population to dissect the genetic architecture of early-season chilling tolerance in the tropical-origin cereal sorghum (Sorghum bicolor [L.] Moench). The NAM resource, developed from reference line BTx623 and three chilling-tolerant Chinese lines, is comprised of 771 recombinant inbred lines genotyped by sequencing at 43,320 single nucleotide polymorphisms. We phenotyped the NAM population for emergence, seedling vigor, and agronomic traits (>75,000 data points from ∼16,000 plots) in multi-environment field trials in Kansas under natural chilling stress (sown 30–45 days early) and normal growing conditions. Joint linkage mapping with early-planted field phenotypes revealed an oligogenic architecture, with 5–10 chilling tolerance loci explaining 20–41% of variation. Surprisingly, several of the major chilling tolerance loci co-localize precisely with the classical grain tannin (Tan1 and Tan2) and dwarfing genes (Dw1 and Dw3) that were under strong directional selection in the US during the 20th century. These findings suggest that chilling sensitivity was inadvertently selected due to coinheritance with desired nontannin and dwarfing alleles. The characterization of genetic architecture with NAM reveals why past chilling tolerance breeding was stymied and provides a path for genomics-enabled breeding of chilling tolerance.Article SummaryChilling sensitivity limits productivity of tropical-origin crops in temperate climates, and remains poorly understood at a genetic level. We developed a nested association mapping resource in sorghum, a tropical-origin cereal, to understand the genetic architecture of chilling tolerance. Linkage mapping of growth traits from early-planted field trials revealed several major chilling tolerance loci, including some colocalized with genes that were selected in the origin of US grain sorghum. These findings suggest chilling sensitivity was inadvertently selected during 20th century breeding, but can be bypassed using a better understanding of the underlying genetic architecture.DisclaimerMention of a trademark, warranty, proprietary product, or vendor does not constitute a guarantee by the USDA and does not imply approval or recommendation of the product to the exclusion of others that may be suitable. USDA is an equal opportunity provider and employer.