Global gene expression analyses of the alkamide-producing plant Heliopsis longipes supports a polyketide synthase-mediated biosynthesis pathway

Abstract

Background Alkamides are plant-specific bioactive molecules. They are low molecular weight N-substituted α-unsaturated acyl amides that display biological explicit activities in different organisms from bacteria, fungi, insects to mammals and plants. The acyl chain has been proposed to be biosynthesized from a fatty acid; however, this has not been demonstrated yet. Heliopsis longipes (Asteraceae) accumulates in root a C10 alkamide called affinin in its roots, but not in leaves. The closely related species Heliopsis annua does not produce alkamides. To elucidate the biosynthetic pathway of the alkamides acyl chain, a comparative global gene expression analysis contrasting roots and leaves of both species was performed. Methods Transcriptomics analysis allowed to identify genes highly expressed in H. longipes roots, but not in tissues and species that do not accumulate alkamides. The first domain searched was the Ketosynthase (KS) domain. The phylogenetic analysis using sequences of the KS domain of FAS and PKS from different organisms, revealed that KS domains of the differentially expressed transcripts in H. longipes roots and the KS domain found in transcripts of Echinacea purpurea, another alkamides producer species, were grouped together with a high bootstrap value of 100%, sharing great similarity. Among the annotated transcripts, we found some coding for the enzymatic domains KS, AT, ACP, DH, OR and TE, which presented higher expression in H. longipes roots than in leaves. The expression level of these genes was further evaluated by qRT-PCR. All unigenes tested showed higher expression in H. longipes roots than in any the other samples. Based on this and considering that the acyl chain of affinin presents unsaturated bonds at even C numbers, we propose a new putative biosynthesis pathway mediated by a four modules polyketide synthase (PKS). Results The global gene expression analysis led to the selection of a set of candidate genes involved in the biosynthesis of the acyl chain of affinin, suggesting that it may be performed by a non-iterative, partially reductive, four module type I PKS complex (PKS alk) previously thought to be absent from the plant kingdom.

The complex genome and adaptive evolution of polyploid Chinese pepper (Zanthoxylum armatum and Zanthoxylum bungeanum)

“…Chinese peppers synthesize some unique alkylamides, especially hydroxy‐α‐sanshool (HAS) and its derivatives, which create a strong tingling sensation and are natural defences against herbivores (Xiong et al ., 1997 ; Yang, 2008 ). The alkylamides are alkyl or aryl amides, biosynthesized from branched‐chain amine and unsaturated fatty acids in acyl transfer reactions (Buitimea‐Cantúa et al ., 2020 ; Rizhsky et al ., 2016 ). The expansion of genes related to unsaturated fatty acid biosynthesis and amino acid decarboxylation (Figure 5a ) provided necessary precursors for alkylamide biosynthesis, such as 3‐ketoacyl‐CoA synthase ( KCS ), 3‐oxoacyl‐[acyl‐carrier‐protein] synthase ( KAS ), acetyl‐CoA acetyltransferase ( ACAT ), fatty acid desaturase ( FAD ) and amino acid decarboxylase ( AADC ).…”

Physiological effects of Acmella ciliata essential oil on root development of Nicotiana tabacum

“…Significantly, alkamides are natural plant products with a wide array of biological activities across multiple phyla. They exhibit properties with antifungal, antibacterial, antimalarial, and insecticidal effects, among others (Buitimea-Cantúa et al, 2020). Furthermore, they play roles in plant growth promotion and defense gene induction, and even interact with intercellular signaling molecules in organisms ranging from humans to bacteria and plants (Buitimea-Cantúa et al, 2020).…”

Variation on a theme: the structures and biosynthesis of specialized fatty acid natural products in plants

“…Here, we give a general overview of the major types of structures and biosynthetic mechanisms known in each of these categories. We note that some alkamide products (reviewed in Greger, 2016) are structurally similar to fatty acids and may appear to be derived from such; however, recent evidence indicates that many of these compounds may be type I polyketide synthase products and thus not derived from fatty acids (Buitimea-Cant ua et al, 2020). Such alkamides are therefore not included in this review.…”