The role of Fragaria vesca homolog of a (Z)-3:(E)-2-hexenal isomerase in the development of green-leafy fruit aroma

The green leaf volatiles (Z)-3-hexenal and (E)-2-hexenal are key components of the characteristic strawberry aroma, an important determinant of consumer preferences. Green leaf volatiles (GLVs) are C6 compounds that impart fresh, green notes and are involved in plant wounding responses. GLV biosynthesis requires several enzymatic steps to convert polyunsaturated fatty acids to C6-aldehydes, alcohols, and esters, respectively. However, the biosynthesis of GLVs in strawberries, such as the isomerization of (Z)-3-hexenal to (E)-2-hexenal, remains poorly understood. In this study, we identified a (Z)-3:(E)-2-hexenal isomerase gene (FvHI) using phylogenetic analysis, characterized its expression in different tissues, and characterized its function using stable transformation. Volatile analysis by gas chromatography–mass spectrometry (GC–MS) of fruits from a Fragaria vesca near-isogenic line (NIL) collection revealed a distinct ratio of (Z)-3-hexenal and (E)-2-hexenal in lines containing Fragaria bucharica introgressions in the distal end of linkage group 5. Consequently, FvHI was located within this genomic region. The coding sequence of FvHI was nearly identical between the recurrent parent and a selected NIL individual containing an introgression in the distal end linkage group 5, indicating that the contrasting ratio of (Z)-3 and (E)-2 GLV isomers may be attributed to transcriptional differences. Accordingly, FvHI expression in ripe fruits was lower in the selected NIL individual than in the recurrent parent. Lastly, FvHI overexpression decreased (Z)-3-hexenal accumulation and increased (E)-2-hexenal accumulation in the recurrent parent and the selected NIL individual. These results suggest that FvHI plays a role in producing the characteristic strawberry aroma by converting (Z)-3-hexenal to (E)-2-hexenal.

This work was funded by the ‘Agencia Estatal de Investigación’ (AEI) (Ministry of Science, Innovation, and Universities; Government of Spain) through grants RTA2013-00010-00-00, PID2020-119052RR-I00 and TED2021-130898B-C32 and through the grant CEX2019-000902-S funded by MICIU/AEI/10.13039/501100011033. This work was also supported by the CERCA Programme/Generalitat de Catalunya and by the “European Union NextGeneration EU/PRTR”. Rong Zhang was supported by a China Scholarship Council predoctoral grant. Dylan Nunally Martinez is a recipient of the predoctoral fellowship HORIZON-MSCA-2021-COFUND-01 rePLANT-GA101081581 Funded by the European Union. Dr. Koskela was supported by a grant from Ella and Georg Ehrnrooth foundation.

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