Candidate Enzymes for Saffron Crocin Biosynthesis Are Localized in Multiple Cellular Compartments

Area of Science:

• Plant Biochemistry
• Metabolic Engineering
• Spice Chemistry

Background:

• Saffron's red color comes from crocins, apocarotenoid glycosides.
• The crocin biosynthetic pathway is crucial for saffron's value.
• Carotenoid cleavage dioxygenase2 (CsCCD2) initiates crocin precursor synthesis.

Purpose of the Study:

• Identify and characterize enzymes involved in crocin biosynthesis.
• Elucidate the roles of aldehyde dehydrogenase and UDP-glycosyltransferase in crocin production.
• Determine the subcellular localization of key enzymes in the pathway.

Main Methods:

• Gene identification and heterologous expression in E. coli.
• In vitro enzymatic assays to determine substrate specificity.
• Protein localization studies in saffron stigmas and N. benthamiana.

Main Results:

• CsALDH3I1 converts crocetin dialdehyde to crocetin, a crocin precursor.
• CsUGT74AD1 glycosylates crocetin into crocins.
• Key enzymes (CsCCD2, CsALDH3I1, CsUGT74AD1) are localized in plastids, ER, and cytoplasm, respectively.

Conclusions:

• The endoplasmic reticulum and cytoplasm act as transit points for crocin precursors.
• Biosynthesis begins in plastids and culminates in vacuolar accumulation.
• This study provides a comprehensive view of the crocin biosynthetic pathway in saffron.