Abstract
Color is an important determinant of pomegranate fruit quality and commercial value. To understand the genetic factors controlling color in pomegranate, chemical, molecular and genetic characterization of a "white" pomegranate was performed. This unique accession is lacking the typical pomegranate color rendered by anthocyanins in all tissues of the plant, including flowers, fruit (skin and arils) and leaves. Steady-state gene-expression analysis indicated that none of the analyzed "white" pomegranate tissues are able to synthesize mRNA corresponding to the PgLDOX gene (leucoanthocyanidin dioxygenase, also called ANS, anthocyanidin synthase), which is one of the central structural genes in the anthocyanin-biosynthesis pathway. HPLC analysis revealed that none of the "white" pomegranate tissues accumulate anthocyanins, whereas other flavonoids, corresponding to biochemical reactions upstream of LDOX, were present. Molecular analysis of the "white" pomegranate revealed the presence of an insertion and an SNP within the coding region of PgLDOX. It was found that the SNP does not change amino acid sequence and is not fully linked with the "white" phenotype in all pomegranate accessions from the collection. On the other hand, genotyping of pomegranate accessions from the collection and segregating populations for the "white" phenotype demonstrated its complete linkage with the insertion, inherited as a recessive single-gene trait. Taken together, the results indicate that the insertion in PgLDOX is responsible for the "white" anthocyanin-less phenotype. These data provide the first direct molecular, genetic and chemical evidence for the effect of a natural modification in the LDOX gene on color accumulation in a fruit-bearing woody perennial deciduous tree. This modification can be further utilized to elucidate the physiological role of anthocyanins in protecting the tree organs from harmful environmental conditions, such as temperature and UV radiation.
Highlights
Pomegranate (Punica granatum L.) is known for its appealing colors, with high color variability reported among pomegranate accessions from different collections around the world, including Iran [1], China [2], Turkey [3], Israel [4], Turkmenistan [5] and the USA [6]
Our analyses indicate that the cause for the "white" phenotype is a mutation in PgLDOX, a structural gene involved in the anthocyanin-biosynthesis pathway in pomegranate
Pigments such as anthocyanins are known for their health-promoting effects
Summary
Pomegranate (Punica granatum L.) is known for its appealing colors, with high color variability reported among pomegranate accessions from different collections around the world, including Iran [1], China [2], Turkey [3], Israel [4], Turkmenistan [5] and the USA [6]. This variability is displayed mostly in the fruit skin, and in the arils and flowers. Other flavonoids and polyphenols might contribute some of the yellowish colors seen in pomegranate fruits [12]
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