TRANSCRIPTOMIC APPLICATION TO IDENTIFY KEY POLYPHENOL OXIDASE GENES PLAYING A ROLE IN BROWNING OF CAVENDISH BANANA (MUSA ACUMINATA CV. CAVENDISH (GENOME AAA)) DURING FRUIT RIPENING

• Main Author: Thufailah Hakim, Nisrina
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/66883
• Institution: Institut Teknologi Bandung

Banana is a climacteric fruit that has the characteristics of increased respiration rate and high ethylene production during ripening. The ripening process that continues to occur in bananas from post-harvest until it arrives in the hands of consumers can result in changes in the taste and visual appearance of bananas, thereby reducing consumer buying interest and consumption of bananas. Cavendish banana (Musa acuminata (AAA genome)) has a post-harvest problem due to the ripening process and particularly senescence, namely browning (change in color to brown and spotting especially on the banana peel). This physiological change involves the enzyme polyphenol oxidase (PPO) which catalyzes the phenolic compounds in bananas to produce melanin. Research on the polyphenol oxidase enzyme during banana ripening is mostly done at the protein level and is still limited at the transcriptome level. Knowledge of the expression of browning-related genes will be helpful in the development of methods to control both ripening and senescence in bananas by silencing genes related to the PPO enzyme synthesis pathway. In this study, RNA-seq data analysis was used to determine the expression profile of the genes that play a role in banana browning. The transcriptomic data used refers to GSE139457 downloaded from NCBI. This data was obtained from the results of RNA sequencing using Illumina HiSeqTM 2000 on banana pulp samples at two ripening points, day 1 (unripe) as control and day 7 (ripe). Based on the results of differentially expressed gene analysis (DEG) with the parameters of Log2FoldChange ? |1| and q-value < 0.05, there are 3837 genes that have increased expression and 3828 genes that have decreased expression on the 7th day. Pathway Enrichment Analysis using all DEGs revealed four genes from the PPO gene family (MaPPO2, MaPPO4, MaPPO1, and MaPPO5) and six browning-related genes (PAL, PAL2, 4CL1, C4H3, HCT, and 4CL3) that involved in the phenylpropanoid biosynthesis pathway. The results of the gene ontology analysis on the ten genes showed that the largest subcategory in biological processes was 'phenylpropanoid metabolic process', in the cellular component category was 'cytosol', as for molecular functions, was 'catechol oxidase activity'. Four PPO genes involved in ripening were then quantified for expression using qPCR. Expression quantification was carried out on the 1st and 7th day of ripening using banana pulp and peel samples. Expression quantification by qPCR showed that the MaPPO2 was significantly down-regulated in banana pulp and peel. On the other hand, MaPPO1 and MaPPO5 genes were found significantly upregulated in banana pulp whereas MaPPO4 and MaPPO5 were significantly upregulated in banana peel (p-value <0.05). MaPPO4 and MaPPO5 which were significantly upregulated on day 7, especially in the peel, were thought to be the key PPO genes involved in the browning of banana fruit. In the future, manipulation of the expression of these PPO genes can be further developed to reduce the browning of bananas due to ripening and senescence processes.