Abstract
The fruit of date palm trees are an important part of the diet for a large portion of the Middle East and North Africa. The fruit is consumed both fresh and dry and can be stored dry for extended periods of time. Date fruits vary significantly across hundreds of cultivars identified in the main regions of cultivation. Most dried date fruit are low in sucrose but high in glucose and fructose. However, high sucrose content is a distinctive feature of some date fruit and affects flavor as well as texture and water retention. To identify the genes controlling high sucrose content, we analyzed date fruit metabolomics for association with genotype data from 120 date fruits. We found significant association of dried date sucrose content and a genomic region that contains 3 tandem copies of the beta‐fructofuranosidase (invertase) gene in the reference Khalas genome, a low‐sucrose fruit. High‐sucrose cultivars including the popular Deglet Noor had a homozygous deletion of two of the 3 copies of the invertase gene. We show the deletion allele is derived when compared to the ancestral allele that retains all copies of the gene in 3 other species of Phoenix. The fact that 2 of the 3 tandem invertase copies are associated with dry fruit sucrose content will assist in better understanding the distinct roles of multiple date palm invertases in plant physiology. Identification of the recessive alleles associated with end‐point sucrose content in date fruit may be used in selective breeding in the future.
Highlights
The date palm (Phoenix dactylifera) is a tree of agricultural significance in a large area stretching from North Africa, through the Middle East and to parts of South Asia
Research on the effect of invertase in tomato fruit revealed accumulation of sucrose was linked to a recessive invertase mutation (Klann, Chetelat, & Bennett, 1993)
By the fully ripe dried stage (Tamr) Barhee dry weight was only 0.25% sucrose while Deglet Noor's dry weight was 58% sucrose (Rygg, 1946; Samarawira, 1983)
Summary
The date palm (Phoenix dactylifera) is a tree of agricultural significance in a large area stretching from North Africa, through the Middle East and to parts of South Asia. Others have shown that these texture categories may relate to the balance of sugars in the dates with higher sucrose associated with the low water retention found in the dry and semi-dry cultivars (Diboun et al, 2015; Mustafa, Harper, & Johnston, 1986; Yahia & Kader, 2011). The date palm genome contains multiple invertases (Al-Dous et al, 2011; Al-Mssallem et al, 2013) for conversion of sucrose in various cellular and physiological pathways; which invertases are involved in dry fruit sucrose content has not been identified. We previously reported the metabolomics analysis of 123 date fruits (Stephan et al, 2018) and their respective genotyping (Thareja et al, 2018) We combine these data sets and analyze the sucrose measurements for association with genetic variants for a total of 120 dates. To understand the possible genetic basis of sucrose content in date fruit, we conducted an association study between the genome-wide genotypes of 120 date cultivars with their sucrose content at the dried fruit stage
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