Riboflavin Accumulation and Characterization of cDNAs Encoding Lumazine Synthase and Riboflavin Synthase in Bitter Melon (Momordica charantia)

Abstract

Riboflavin (vitamin B2) is the universal precursor of the coenzymes flavin mononucleotide and flavin adenine dinucleotide--cofactors that are essential for the activity of a wide variety of metabolic enzymes in animals, plants, and microbes. Using the RACE PCR approach, cDNAs encoding lumazine synthase (McLS) and riboflavin synthase (McRS), which catalyze the last two steps in the riboflavin biosynthetic pathway, were cloned from bitter melon (Momordica charantia), a popular vegetable crop in Asia. Amino acid sequence alignments indicated that McLS and McRS share high sequence identity with other orthologous genes and carry an N-terminal extension, which is reported to be a plastid-targeting sequence. Organ expression analysis using quantitative real-time RT PCR showed that McLS and McRS were constitutively expressed in M. charantia, with the strongest expression levels observed during the last stage of fruit ripening (stage 6). This correlated with the highest level of riboflavin content, which was detected during ripening stage 6 by HPLC analysis. McLS and McRS were highly expressed in the young leaves and flowers, whereas roots exhibited the highest accumulation of riboflavin. The cloning and characterization of McLS and McRS from M. charantia may aid the metabolic engineering of vitamin B2 in crops.

Riboflavin Accumulation and Molecular Characterization of cDNAs Encoding Bifunctional GTP Cyclohydrolase II/3,4-Dihydroxy-2-Butanone 4-Phosphate Synthase, Lumazine Synthase, and Riboflavin Synthase in Different Organs of Lycium chinense Plant

“…In addition, the four riboflavin biosynthetic genes showed significantly higher expression in the red fruits than in the green fruits; however, red fruits did not show higher accumulation of riboflavin content than green fruits. In our previous study, we also found that the transcription levels of riboflavin biosynthetic genes were not correlated with the accumulation of riboflavin in different tissues of Momordica charantia [13]. We hypothesize that there are several isoforms of riboflavin biosynthetic genes which have tissue-specific expression in plants.…”

“…The final step of the riboflavin biosynthetic pathway is mediated by riboflavin synthase (RS), which catalyzes the disproportionation of 6,7-dimethyl-8-ribityllumazine, affording riboflavin and 5-amino-6-ribitylamino-2,4(1 H ,3 H )-pyrimidinedione, which is recycled in the biosynthetic pathway [11]. Over the past 15 years, several researchers have investigated riboflavin biosynthesis by cloning a bifunctional protein with GCHYII and DHBP in Arabidopsis [9]; characterization of LS and RS has been conducted in spinach, tobacco, and bitter melon [12,13]. Recently, the availability of next-generation sequencing technologies has allowed the extensive investigation of the genes related to the riboflavin biosynthetic pathway in plants.…”

Smart Aptamer and Protein Functionalized Poly(N-isopropyl acrylamide) Materials for Selective Extraction of Riboflavin in Beer

“…Riboflavin is an essential vitamin in human nutrition occurring in a wide variety of food products, and it is produced biotechnologically and used in vitamin enriched food and food supplements. [1][2][3][4] Additionally, riboflavin is an important biological redox cofactor that can act as the universal precursor of the flavin adenine dinucleotide and coenzyme flavin mononucleotide. 5 In view of this, riboflavin is indispensable for the activity of a wide variety of metabolic enzymes in microbes, plants and animals, and it is very important for human and animal health.…”