Small RNAs, Degradome, and Transcriptome Sequencing Provide Insights into Papaya Fruit Ripening Regulated by 1-MCP

Genome-wide identification of MAPK family in papaya (Carica papaya) and their involvement in fruit postharvest ripening

BACKGROUND

Papaya (Carica papaya) is an economically important fruit cultivated in the tropical and subtropical regions of China. However, the rapid softening rate after postharvest leads to a short shelf-life and considerable economic losses. Accordingly, understanding the mechanisms underlying fruit postharvest softening will be a reasonable way to maintain fruit quality and extend its shelf-life.

RESULTS

Mitogen-activated protein kinases (MAPKs) are conserved and play essential roles in response to biotic and abiotic stresses. However, the MAPK family remain poorly studied in papaya. Here, a total of nine putative CpMAPK members were identified within papaya genome, and a comprehensive genome-wide characterization of the CpMAPKs was performed, including evolutionary relationships, conserved domains, gene structures, chromosomal locations, cis-regulatory elements and expression profiles in response to phytohormone and antioxidant organic compound treatments during fruit postharvest ripening. Our findings showed that nearly all CpMAPKs harbored the conserved P-loop, C-loop and activation loop domains. Phylogenetic analysis showed that CpMAPK members could be categorized into four groups (A-D), with the members within the same groups displaying high similarity in protein domains and intron-exon organizations. Moreover, a number of cis-acting elements related to hormone signaling, circadian rhythm, or low-temperature stresses were identified in the promoters of CpMAPKs. Notably, gene expression profiles demonstrated that CpMAPKs exhibited various responses to 2-chloroethylphosphonic acid (ethephon), 1-methylcyclopropene (1-MCP) and the combined ascorbic acid (AsA) and chitosan (CTS) treatments during papaya postharvest ripening. Among them, both CpMAPK9 and CpMAPK20 displayed significant induction in papaya flesh by ethephon treatment, and were pronounced inhibition after AsA and CTS treatments at 16 d compared to those of natural ripening control, suggesting that they potentially involve in fruit postharvest ripening through ethylene signaling pathway or modulating cell wall metabolism.

CONCLUSION

This study will provide some valuable insights into future functional characterization of CpMAPKs, and hold great potential for further understanding the molecular mechanisms underlying papaya fruit postharvest ripening.

Small RNA sequencing and identification of papaya (Carica papaya L.) miRNAs with potential cross-kingdom human gene targets

Several studies have demonstrated potential role of plant-derived miRNAs in cross-kingdom species relationships by transferring into non-plant host cells to regulate certain host cellular functions. How nutrient-rich plants regulate host cellular functions, which in turn alleviate physiological and disease conditions in the host remains to be explored in detail. This computational study explores the potential targets, putative role, and functional implications of miRNAs derived from Carica papaya L., one of the most cultivated tropical crops in the world and a rich source of phytochemicals and enzymes, in human diet. Using the next-generation sequencing, -Illumina HiSeq2500, ~ 30 million small RNA sequence reads were generated from C. papaya young leaves, resulting in the identification of a total of 1798 known and 49 novel miRNAs. Selected novel C. papaya miRNAs were predicted to regulate certain human targets, and subsequent annotation of gene functions indicated a probable role in various biological processes and pathways, such as MAPK, WNT, and GPCR signaling pathways, and platelet activation. These presumptive target gene in humans were predominantly linked to various diseases, including cancer, diabetes, mental illness, and platelet disorder. The computational finding of this study provides insights into how C. papaya-derived miRNAs may regulate certain conditions of human disease and provide a new perspective on human health. However, the therapeutic potential of C. papaya miRNA can be further explored through experimental studies.

Foodomics: Current and Future Perspectives in Food Analysis

Climate change, an increase in population, and the recent pandemic crisis triggered by SARS-CoV-2 have all contributed to a period of global problems [...].

Genomic Approaches for Improvement of Tropical Fruits: Fruit Quality, Shelf Life and Nutrient Content

The breeding of tropical fruit trees for improving fruit traits is complicated, due to the long juvenile phase, generation cycle, parthenocarpy, polyploidy, polyembryony, heterozygosity and biotic and abiotic factors, as well as a lack of good genomic resources. Many molecular techniques have recently evolved to assist and hasten conventional breeding efforts. Molecular markers linked to fruit development and fruit quality traits such as fruit shape, size, texture, aroma, peel and pulp colour were identified in tropical fruit crops, facilitating Marker-assisted breeding (MAB). An increase in the availability of genome sequences of tropical fruits further aided in the discovery of SNP variants/Indels, QTLs and genes that can ascertain the genetic determinants of fruit characters. Through multi-omics approaches such as genomics, transcriptomics, metabolomics and proteomics, the identification and quantification of transcripts, including non-coding RNAs, involved in sugar metabolism, fruit development and ripening, shelf life, and the biotic and abiotic stress that impacts fruit quality were made possible. Utilizing genomic assisted breeding methods such as genome wide association (GWAS), genomic selection (GS) and genetic modifications using CRISPR/Cas9 and transgenics has paved the way to studying gene function and developing cultivars with desirable fruit traits by overcoming long breeding cycles. Such comprehensive multi-omics approaches related to fruit characters in tropical fruits and their applications in breeding strategies and crop improvement are reviewed, discussed and presented here.