FAD2 Gene Radiation and Positive Selection Contributed to Polyacetylene Metabolism Evolution in Campanulids

Abstract

Polyacetylenes (PAs) are bioactive, specialized plant defense compounds produced by some species in the eudicot clade campanulids. Early steps of PA biosynthesis are catalyzed by Fatty Acid Desaturase 2 (FAD2). Canonical FAD2s catalyze desaturation, but divergent forms can catalyze hydroxylation, conjugation, acetylenation, and epoxygenation. These alternate reactions give rise to valuable unusual fatty acids, including the precursors to PAs. The extreme functional diversity of FAD2 enzymes and the origin of PA biosynthesis are poorly understood from an evolutionary perspective. We focus here on the evolution of the FAD2 gene family. We uncovered a core eudicot-wide gene duplication event giving rise to two lineages: FAD2a and FAD2-b. Independent neofunctionalizations in both lineages have resulted in functionally diverse FAD2-LIKEs involved in unusual fatty acid biosynthesis. We found significantly accelerated rates of molecular evolution in FAD2-LIKEs and use this metric to provide a list of uncharacterized candidates for further exploration of FAD2 functional diversity. FAD2-a has expanded extensively in Asterales and Apiales, two main clades of campanulids, by ancient gene duplications. Here, we detected positive selection in both Asterales and Apiales lineages, which may have enabled the evolution of PA metabolism in campanulids. Together, these findings also imply that yet uncharacterized FAD2-a copies are involved in later steps of PA biosynthesis. This work establishes a robust phylogenetic framework in which to interpret functional data and to direct future research into the origin and evolution of PA metabolism.

Molecular and biochemical analyses of avocado (Persea americana) reveal differences in the oil accumulation pattern between the mesocarp and seed during the fruit developmental period

“…The enzyme encoded by FAD2 catalyzes the introduction of a second double bond in oleic acid, which generates polyunsaturated linoleic acid [67]. In our study, two PaFAD2 paralogs were expressed in the avocado mesocarp and seed, with higher transcription levels in the developing mesocarp than in the developing seed, consistent with the differences in the C18:2 contents between these two tissues ( Fig.…”

Arabidopsis ACYL‐ACTIVATING ENZYME 9 (AAE9) encoding an isobutyl‐CoA synthetase is a key factor connecting branched‐chain amino acid catabolism with iso‐branched wax biosynthesis

“…In our study, AAE9 preferentially catalyses short branched‐chain fatty acid iBA. To find out if its orthologues displayed conserved functions among different plants, we performed a Blast search against a custom database using AAE9 as the query (Feng et al ., 2019), this query included the proteomes of algae, bryophytes, ferns, gymnosperms and angiosperms. Consistent with previous studies (Shockey et al ., 2003), AAE9 was grouped together with AAE10 (AT1G21530) and AAE4 (AT1G77240), which are thought to have been derived from recent gene duplications (Fig.…”

“…To explore the origin and diversification of AAE gene family in green plants, we performed a Blast search against a custom database (Feng et al ., 2019), the Blast search included the proteome of algae, bryophytes, ferns, gymnosperms and angiosperms. B lastp with AAE9 (AT1G21540) as query was performed to retrieve AAE9 homologues from the database.…”

Transformation and Characterization of Δ12-Fatty Acid Acetylenase and Δ12-Oleate Desaturase Potentially Involved in the Polyacetylene Biosynthetic Pathway from Bidens pilosa

“…Polyacetylenes have two or more carbon-carbon triple bonds or alkynyl functional groups and are mainly derived from fatty acid and polyketide precursors, and polyacetylenic compounds possess antibacterial, antifungal, or antitumor properties [10,11]. More than 2000 polyacetylenes have been identified, and more than 1100 compounds with diverse acetylenic structures have been found in the plant family Asteraceae [12].…”

“…More than 2000 polyacetylenes have been identified, and more than 1100 compounds with diverse acetylenic structures have been found in the plant family Asteraceae [12]. The crepenynate pathway has been suggested to be a major route for polyacetylene biosynthesis and has been investigated in fungi and plants over the past several decades [11,12]. Several genes related to this pathway, such as the desaturases and acetylenases, have been cloned and characterized.…”