Abstract
Strawberries produce numerous volatile compounds that contribute to the unique flavors of fruits. Among the many volatiles, γ-decalactone (γ-D) has the greatest contribution to the characteristic fruity aroma in strawberry fruit. The presence or absence of γ-D is controlled by a single locus, FaFAD1. However, this locus has not yet been systematically characterized in the octoploid strawberry genome. It has also been reported that the volatile content greatly varies among the strawberry varieties possessing FaFAD1, suggesting that another genetic factor could be responsible for the different levels of γ-D in fruit. In this study, we explored the genomic structure of FaFAD1 and determined the allele dosage of FaFAD1 that regulates variations of γ-D production in cultivated octoploid strawberry. The genome-wide association studies confirmed the major locus FaFAD1 that regulates the γ-D production in cultivated strawberry. With the hybrid capture-based next-generation sequencing analysis, a major presence–absence variation of FaFAD1 was discovered among γ-D producers and non-producers. To explore the genomic structure of FaFAD1 in the octoploid strawberry, three bacterial artificial chromosome (BAC) libraries were developed. A deletion of 8,262 bp was consistently found in the FaFAD1 region of γ-D non-producing varieties. With the newly developed InDel-based codominant marker genotyping, along with γ-D metabolite profiling data, we revealed the impact of gene dosage effect for the production of γ-D in the octoploid strawberry varieties. Altogether, this study provides systematic information of the prominent role of FaFAD1 presence and absence polymorphism in producing γ-D and proposes that both alleles of FaFAD1 are required to produce the highest content of fruity aroma in strawberry fruit.
Highlights
Flavor and aroma are important characteristics of fruit quality in the cultivated octoploid strawberry (Fragaria × ananassa)
Single-marker analysis with AX-166512929 that is closely associated with the FaFAD1 locus suggests that this quantitative trait loci (QTL) is responsible for the natural variations of γ-D in the octoploid strawberry accessions (Figure 2B)
Strawberry fruit has one of the most complex aromas and it has been reported that differences in aroma volatiles can improve strawberry fruit quality (Pelayo-Zaldivar et al, 2005; Dong et al, 2013)
Summary
Flavor and aroma are important characteristics of fruit quality in the cultivated octoploid strawberry (Fragaria × ananassa). The major aroma compounds are identified as esters, lactones, furanones, sulfur compounds, and terpenoids (Perez et al, 1992; Zabetakis and Holden, 1997; Dong et al, 2013; CruzRus et al, 2017) Among these flavor and aroma compounds, γ-decalactone (γ-D) has a desirable “fruity,” “sweet,” or “peachlike” aroma in strawberry fruit (Larsen et al, 1992; Jetti et al, 2007; Ulrich et al, 2007; Jouquand et al, 2008; Olbricht et al, 2008). Presence or absence of γ-D in strawberry fruit is controlled by a single gene, FaFAD1, encoding omega-6 fatty acid desaturase This gene was mapped to the linkage group III (LG3) in the octoploid strawberry (Zorrilla-Fontanesi et al, 2012; Chambers et al, 2014; Sánchez-Sevilla et al, 2014). Additional sequencing and comparative analyses are required to characterize the genomic structure of the FaFAD1 region
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