Papaya
Papaya (Carica papaya L.), once called the fruit of angels by Christopher Columbus, is one of the most nutritional fruits, rich in vitamins, carotenoids, flavonoids and other antioxidants with wide range of health benefits. These natural antioxidants include polyphenols, carotenoids, and flavonoids, which are mainly plant secondary metabolites that are also important determinants of food quality, like taste and colour.
Papaya is an important fruit crop in Malaysia with different varieties, in which the most popular is "Sekaki" and "Eksotika". Apart from traditional breeding, tissue culture is critical for crop improvement of papaya. |
Papaya is polygamous and dioecious with three types of flowers, namely male, female, and hermaphrodite.
In vitro Tissue Culture
Haploid Culture
Characterisation of microspores from different stages of hermaphrodite and male flowers
Attempts to induce haploid culture from microspores of male flowers were unsuccessful.
Polyploid Culture
Colchicine induction
Various methods were attempted to induce polyploidy in calli, shoots, and seeds but low success rates.
Endosperm culture
This study demonstrated that it is possible to generate triploid calli from endosperm culture of local papaya variety.
However, the callus induction media need to be further optimised through systematic testing of different PGR concentrations.
This work will serve as a starting point for further study.
However, the callus induction media need to be further optimised through systematic testing of different PGR concentrations.
This work will serve as a starting point for further study.
Somatic Embryogenic Culture
Biotechnological application
Phytonutrient improvement via RNAi genetic engineering
Previous studies showed phytonutrient improvement without affecting quality in tomato fruit and rapeseed through the suppression of DE-ETIOLATED-1 (DET1), a negative regulator in photomorphogenesis.
This study is conducted to study the effects of DET1 gene suppression in papaya embryogenic callus. Immature zygotic embryos were transformed with constitutive expression of a hairpin DET1 construct (hpDET1). PCR screening of transformed calli and reverse transcription quantitative PCR (RT-qPCR) verified that DET1 gene downregulation in two of the positive transformants. |
High-throughput cDNA 3′ ends sequencing on DET1-suppressed and control calli for transcriptomic analysis of global gene expression identified a total of 452 significant (FDR < 0.05) differentially expressed genes (DEGs) upon DET1 suppression.
The 123 upregulated DEGs were mainly involved in phenylpropanoid biosynthesis and stress responses, compared to 329 downregulated DEGs involved in developmental processes, lipid metabolism, and response to various stimuli.
Significance
This is the first proof-of-concept experiment which demonstrated that the manipulation of photo-regulated pathway can increase gene expression of secondary metabolite biosynthesis in papaya callus, consistent with previous reports in tomato fruit and rapeseed. Further study using a fruit-specific promoter in papaya is needed to avoid non-desired defect of constitutive DET1 suppression. This study supports the possibility in manipulating light-regulated pathway as an alternative to engineering targeted biosynthetic pathways for the improvement of phytonutrient in tropical fruit crops.
References
Book
Grants
- Jamaluddin ND, Rohani ER, Normah MN & Goh H-H* (2019) Transcriptome-wide effect of DE-ETIOLATED1 (DET1) suppression in embryogenic callus of Carica papaya. Journal of Plant Research 132(2), 181-195.
- Jamaluddin ND, Normah MN & Goh H-H* (2017) Transcriptome analysis of Carica papaya embryogenic callus upon De-etiolated 1 (DET1) gene suppression. Genomics Data, 12:120-121.
- Jamaluddin ND, Normah MN & Goh H-H* (2017) Genome-wide transcriptome profiling of Carica papaya L. embryogenic callus. Physiology and Molecular Biology of Plants, 23(2), 357-368. PDF
Book
- Jamaluddin N.D., Saad M.F.M. & Goh H-H. (2020) Penambahbaikan fitonutrien betik melalui kultur tisu, transformasi genetik, RNAi dan transkriptomik. UKM Press ISBN 9789672510307
Grants
- INTEGRATED APPROACH TO IMPROVE LOCAL PAPAYA VARIETIES THROUGH ANTHER AND ENDOSPERM CULTURE - ScienceFund MOSTI: 02-01-02-SF0907 [1 Oct 2012 – 30 Sep 2015] - PI
- NOVEL APPROACH TO THE ENHANCEMENT OF CAROTENOID CONTENT IN PAPAYA - Research University Grant: GGPM-2011-053 [19 Dec 2011 – 18 Dec 2013] - PI
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