Xanthophyll esterases in association with fibrillins control the stable storage of carotenoids in yellow flowers of rapeseed (Brassica juncea)

Abstract

Summary Biosynthesis, stabilization, and storage of carotenoids are vital processes in plants that collectively contribute to the vibrant colors observed in flowers and fruits. Despite its importance, the carotenoid storage pathway remains poorly understood and lacks thorough characterization. We identified two homologous genes, BjA02.PC1 and BjB04.PC2, belonging to the esterase/lipase/thioesterase (ELT) family of acyltransferases. We showed that BjPCs in association with fibrillin gene BjFBN1b control the stable storage of carotenoids in yellow flowers of Brassica juncea. Through genetic, high‐resolution mass spectrometry and transmission electron microscopy analyses, we demonstrated that both BjA02.PC1 and BjB04.PC2 can promote the accumulation of esterified xanthophylls, facilitating the formation of carotenoid‐enriched plastoglobules (PGs) and ultimately producing yellow pigments in flowers. The elimination of BjPCs led to the redirection of metabolic flux from xanthophyll ester biosynthesis to lipid biosynthesis, resulting in white flowers for B. juncea. Moreover, we genetically verified the function of two fibrillin genes, BjA01.FBN1b and BjB05.FBN1b, in mediating PG formation and demonstrated that xanthophyll esters must be deposited in PGs for stable storage. These findings identified a previously unknown carotenoid storage pathway that is regulated by BjPCs and BjFBN1b, while offering unique opportunities for improving the stability, deposition, and bioavailability of carotenoids.

Involvement of Transcription Factors and Regulatory Proteins in the Regulation of Carotenoid Accumulation in Plants and Algae

“…Carotenoids are usually highly esterified in fruits, flowers, and the astaxanthin-accumulating Haematococcus pluvialis. The esterification of carotenoids can enhance carotenoid stability and increase their lipophilic properties, thus facilitating their sequestration into carotenoid-containing structures . In flower petals and ripe fruits, the breakdown of the thylakoid is accompanied by the accumulation of carotenoids in the membrane along with synthesis of membranes as sites for carotenoid biosynthesis, as well as an increased number and size of plastoglobules .…”

“…The esterification of carotenoids can enhance carotenoid stability and increase their lipophilic properties, thus facilitating their sequestration into carotenoid-containing structures. 115 In flower petals and ripe fruits, the breakdown of the thylakoid is accompanied by the accumulation of carotenoids in the membrane along with synthesis of membranes as sites for carotenoid biosynthesis, as well as an increased number and size of plastoglobules. 116 In tomato, chromoplast-specific carotenoid-associated protein (CHRC) appeared to be important for the sequestration and stabilization of carotenoids.…”

An amphipathic helix drives interaction of Fibrillins with plastoglobule lipid droplets

“…Localization of certain proteins on cytosolic LDs is sensitive to protein crowding, in which such proteins are outcompeted by stronger-binding proteins (33,38,74). Furthermore, plastoglobule localization of certain proteins may be dependent on protein-protein mediated recruitment (3,4,26,27). To investigate whether AtFBN1a may influence the plastoglobule proteome through protein crowding or protein recruitment we characterized the quantitative proteome of plastoglobules using the LC-MS/MS analyses of isolated plastoglobule from N. benthamiana transient transformations described above.…”

“…FBNs share a lipocalin domain characterized by a β-barrel that forms a hydrophobic cavity capable of binding small hydrophobic ligands (19)(20)(21), and are believed to provide a structural role for the plastoglobule. Investigation of mutant lines in plastoglobule-targeted FBNs implicate them in stress tolerance (3,4,14,(22)(23)(24), as well as recruitment of proteins (such as the jasmonate biosynthetic pathway or carotenoid metabolism) to plastoglobules (3,4,13,14,(25)(26)(27)(28).…”

Multi‐omics analyses reveal the importance of chromoplast plastoglobules in carotenoid accumulation in citrus fruit

“…Based on proteome analyses, FBNs make up ~50% of the protein mass of PGs in Arabidopsis (Lundquist et al, 2012). Although it is well known that FBNs are involved in carotenoid storage, the pathways modulating the stabilization of carotenoids have only recently started to be elucidated (Li et al, 2023). These data suggest that the esterification of carotenoids may be important to this process via members of the esterase/ lipase/thioesterase (ELT) gene family.…”