Biology subjects

Malherbe, L.

Publications and source records attributed to Malherbe, L..

4 recordsLinked to original sources

bioRxiv2026

Discovery of Scrophularia nodosa harpagoside synthase, a novel BAHD cinnamoyltransferase, bridges a key gap in the iridoid biosynthetic pathway

Harpagoside, a high-value anti-inflammatory iridoid compound, is traditionally extracted from the roots of Harpagophytum procumbens (Pedaliaceae, Lamiales), a Southern African desert plant widely used in traditional medicine but currently threatened by overexploitation. Scrophularia nodosa (Scrophulariaceae, Lamiales) is a perennial annual plant widely distributed in Western Europe and accumulates several iridoid compounds with known biological activities, such as catalpol, aucubin, harpagide and particularly harpagoside. We gathered extensive genomic and transcriptomics resources for this species and aimed at deciphering the biosynthetic pathway leading to the most abundant iridoid in S. nodosa, harpagoside. We found that the early iridoid pathway is well conserved with other iridoid-producing plants and validated the enzyme activities by transient co-expression in N. benthamiana. Investigation into the large BAHD family showed subclade 6i expanding in Scrophulariaceae, with an atypical VYPWG motif instead of the canonical DFGWG. In this branch, we discovered and characterized harpagoside synthase, a BAHD-type cinnamoyl transferase enzyme showing unique high specificity to the uncommon cinnamoyl-CoA acyl donor and catalyzing the final step of harpagoside biosynthesis. These results establish S. nodosa as a new model to investigate unexplored branches of the iridoids metabolism, and are a first step towards sustainable harpagoside and high-value cinnamoyl-containing conjugates production.

plant biology↗

bioRxiv2026

The CUTIN SYNTHASE enzyme family was a key driver of cuticle emergence in land plants

The plant cuticle is a key adaptation acquired during the colonization of land. It forms a hydrophobic barrier at the interface with the environment, fulfilling essential protective and developmental functions. Despite its evolutionary significance and central role in land plant biology, the determinants that drove the emergence of the cuticle remain poorly understood. Here, we show that the CUTIN SYNTHASE (CUS) enzyme family, which synthesises the lipidic polyester that forms the structural framework of the cuticle in flowering plants, originated in a common ancestor of land plants, concomitant with terrestrialization. Using the moss Physcomitrium patens, we further demonstrate that CUS function is conserved among land plants. Inactivation of CUS genes disrupts gametophore development, the first tissue forming a cuticle during the moss life cycle, and compromises cuticle integrity. We also show that P. patens CUS enzymes localize to the apoplast, where they mediate the formation of a 10,16-dihydroxyhexadecanoic acid polyester using 2-mono-(10,16-dihydroxyhexadecanoyl)glycerol as substrate. Overall, our results reveal the conservation of CUS catalytic and physiological functions over 500 million years and support a pivotal role for this enzyme family in the emergence of the cuticle in an ancestral land plant during terrestrialization. SIGNIFICANCEThe cuticle is a hallmark of land plants that fulfills essential roles, ranging from protection to development. Elucidating the mechanisms underlying its emergence and formation therefore has the potential to reveal fundamental aspects of land plant evolution and biology. Here, we show that the CUTIN SYNTHASE (CUS) enzyme family, which catalyzes the formation of the cuticle framework in flowering plants, arose in an ancestor of land plants during terrestrialization. Using the moss Physcomitrium patens, we further demonstrate that CUS function has been conserved for 500 million years across bryophytes and tracheophytes. We propose that the emergence of the CUS family was a key event in establishing the plant cuticle during terrestrialization.

plant biology↗

bioRxiv2024

Rice JASMONIC ACID OXIDASES (OsJAO) control resting jasmonate metabolism to promote development and repress basal immune responses

Recent research has established that catabolic conversions within the jasmonate pathway have significant consequences on hormone signaling output. In dicotyledonous plants, the jasmonic acid oxidase (JAO) catabolic route is endowed with a regulatory function by diverting jasmonic acid (JA) towards hydroxylation, at the expense of its conjugation into the bioactive jasmonoyl-isoleucine (JA-Ile) hormone. Here we functionally characterized the JAO pathway in rice (Oryza sativa) and demonstrate its prevalent function in promoting growth and attenuating JA responses in vegetative tissues. The rice genome contains four JAO-related homologs of which three generated hydroxy-JA in vitro and reverted the high defense phenotype when expressed in the Arabidopsis jao2-2 mutant. By generating and analyzing a series of single to quadruple rice jao mutants, we show the incremental effect of gradual JAO depletion on JA metabolism, basal defense levels, growth inhibition, fitness and global metabolic reprogramming. JAO-deficient lines were significantly growth-retarded at the juvenile stage, while recovering a near wild-type vegetative development after three months, where they exhibited a enhanced resistance to virulent and avirulent strains of Magnaporthe oryzae, the causal agent of fungal blast disease. Our findings identify the JAO pathway as an integral component of rice JA homeostasis and an important determinant of the growth-defense tradeoff. They demonstrate its conserved regulatory function in monocots and open possibilities for modulating selectively basal JA responses in a major cereal crop. Natural variation in JAO activity could also be explored as a mechanism underlying varying levels of JA signaling output in rice.

plant biology↗

bioRxiv2023

An ancient role for the CYP73 gene family in t-cinnamic acid 4-hydroxylation, phenylpropanoid biosynthesis and embryophyte development

The phenylpropanoid pathway is a plant metabolism intimately linked to the transition to terrestrial life. It produces phenolic compounds that play essential roles in stress mitigation and ecological interactions. The pathway also provides the building blocks for hydrophobic polymers that form apoplastic diffusion barriers and make up a significant fraction of the land plant biomass. Despite its significance in embryophytes (i.e., land plants), the origin and evolutionary history of the phenylpropanoid pathway remain poorly understood. In particular, little is known about the organization and function of the pathway in bryophytes, the non-vascular embryophytes. In this study, we conducted a multidisciplinary analysis of the CYP73 gene family that encodes t-cinnamic acid 4-hydroxylase (C4H), the first plant-specific enzyme in the pathway. Our results indicate that C4H activity originated with the emergence of the CYP73 gene family in an ancestor of land plants and was supported by an arginine residue that stabilizes its substrate in the active site. C4H deficiency in the moss Physcomitrium patens, the liverwort Marchantia polymorpha and the hornwort Anthoceros agrestis resulted in a shortage of phenylpropanoids and abnormal plant development. The latter could be rescued in the moss by the exogenous supply of p-coumaric acid, the product of C4H. Our findings establish the emergence of the CYP73 gene family as a foundational event for the development of the canonical plant phenylpropanoid pathway and underscores the deep-rooted conservation of the C4H enzyme function in embryophyte biology.

plant biology↗