Gene expression and enzyme activities of the D-mannose/L-galactose pathway influence L-ascorbic acid content in Myrciaria dubia

Abstract

The aim of this work was to elucidate the molecular and biochemical mechanisms that control L-ascorbic acid (AsA) content variation in Myrciaria dubia. The AsA was quantified by high-performance liquid chromatography, gene expression by real-time quantitative PCR, and enzyme activities by spectrophotometric methods from leaves and immature fruits of two genotypes (Md-60,06 and Md-02,04) with pronounced (about 2 times) differences in the AsA content. In either genotype, the fruit peel had ~ 1.5 times more AsA than the fruit pulp and ~ 15.0 times more than the leaf. All tissues examined demonstrated the capability for AsA biosynthesis through the D-mannose/L-galactose pathway because mRNAs of the six key genes [GDP-D-mannose pyrophosphorylase (GMP), GDP-D-mannose-3ꞌ,5ꞌ-epimerase (GME), GDP-L-galactose phosphorylase (GGP), L-galactose-1-phosphate phosphatase (GPP), L-galactose dehydrogenase (GDH), and L-galactono-1-4-lactone dehydrogenase (GLDH)] and catalytic activities of the corresponding enzymes (GMP, GDH, and GLDH) were detected. The differential expressions of genes and enzyme activities mostly correlated with the respective AsA content. Thus, the expression of several genes of the D-mannose/ L-galactose pathway determined the AsA content variation in tissues of M. dubia.

Kiwifruit MYBS1‐like and GBF3 transcription factors influence l‐ascorbic acid biosynthesis by activating transcription of GDP‐L‐galactose phosphorylase 3

“…Considering the important role of AsA in human health, studies on the molecular mechanism underlying AsA accumulation in the fruit of some very high AsA-containing species, those with c. 500-3000 mg 100 g À1 FW could help breeders increase the AsA content of crop plants in the future (Macknight et al, 2017). Examples of these AsA superfruits include some species of the Actinidia genus (kiwifruit), Rosa roxburghii (chestnut rose), Myrciaria dubia (camu-camu) (Castro et al, 2015), Terminalia ferdinandiana (Kakadu plum) and Malpighia glabra (acerola) (Badejo et al, 2007). Indeed the high AsA trait carried by A. eriantha recently has been mapped to chromosome 26 and segregates as a large nonrecombinant portion of chromosome in A. eriantha 9 A. deliciosa 9 A. chinensis hybrids (McCallum et al, 2019).…”

A chromosome‐level genome assembly provides insights into ascorbic acid accumulation and fruit softening in guava (Psidium guajava)

“…Genes encoding downstream biosynthesis enzymes exhibited a positive correlation between expression level and ascorbic acid content in fruits (Figure 5). This result is similar to a previous report in a closely related species, Myrciaria dubia (Myrtaceae) (Castro et al ., 2015a). In other pathways, however, only one member of GalUR (D‐galacturonate reductase) and two of MIOX (myo‐inositol oxygenase) had detectable expression (Figure S16a).…”

Ascorbic acid metabolism during sweet cherry (Prunus avium) fruit development

“…GGP has been supposed to be the key regulatory gene of the L-galactose pathway for AsA biosynthesis in kiwifruit [ 32 ] and apple [ 33 ]. The expression of GalLDH mostly correlated with the respective AsA content levels in different Myrciaria dubia tissues [ 34 ].…”