Biology subjects

Joubes, J.

Publications and source records attributed to Joubes, J..

4 recordsLinked to original sources

bioRxiv2025

A dual component system instructs membrane hydrolysis during the final stages of plant autophagy

Autophagy is an intracellular catabolic process conserved across eukaryotes and critical for plant stress tolerance. Upon their delivery in the vacuole, how autophagic bodies containing cargo are hydrolyzed to warrant autophagy degradation remains poorly characterized. Here, we identify two Arabidopsis phospholipases as core components of the autophagy machinery. We find that LCAT3 and LCAT4 traffic to the vacuolar lumen and converge on autophagic bodies using differential pathways, placing them on the outer and inner side of the vesicle, respectively. Double knockouts lcat3,4 accumulate autophagic bodies and show reduced autophagy activity. In vivo reconstitution demonstrates that LCAT3 can hydrolyze the membrane of autophagic bodies, enabling the activity of LCAT4 to enhance this process. In sum, our work reveals that the concerted action of a multi-component system is required for the efficient and specific disruption of autophagic bodies as an obligatory step for the completion of the autophagy pathway.

plant biology↗

bioRxiv2020

Hello darkness, my old friend: 3-Ketoacyl-Coenzyme A Synthase4 is a branch point in the regulation of triacylglycerol synthesis in Arabidopsis by re-channeling fatty acids under carbon starvation

Due to their sessile lifestyle, plants have evolved unique mechanisms to deal with environmental challenges. Under stress, plant lipids are important as alternative sources of carbon and energy when sugars or starch are limited. Here, we applied combined heat and darkness and extended darkness to a panel of [~] 300 Arabidopsis accessions to study lipid remodeling under carbon starvation. Natural allelic variation at 3-KETOACYL-COENZYME A SYNTHASE4 (KCS4), a gene encoding for an enzyme involved in very long chain fatty-acid (VLCFA) synthesis, underlies a differential accumulation of polyunsaturated triacylglycerols (puTAGs) under stress. Ectopic expression in yeast and plants proved that KCS4 is a functional enzyme localized in the ER with specificity for C22 and C24 saturated acyl-CoA. Allelic mutants and transient overexpression in planta revealed the differential role of KCS4 alleles in VLCFA synthesis and wax coverage, puTAG accumulation and biomass. Moreover, the region harboring KCS4 is under high selective pressure and allelic variation at KCS4 correlated with environmental parameters from the locales of Arabidopsis accessions. Our results provide evidence that KCS4 plays a decisive role in the subsequent fate of fatty acids released from chloroplast-membrane lipids under carbon starvation. This work sheds light on both plant response mechanisms and the evolutionary events shaping the lipidome under carbon starvation. One sentence summaryNatural variation at KCS4 underlies a differential accumulation of polyunsaturated triacylglycerols under carbon starvation, by acting as a regulatory branch point in the fate of fatty acids.

genetics↗

bioRxiv2020

Plastidic Δ6 Fatty-Acid Desaturases With Distinctive Substrate Specificity Regulate The Pool Of C18-PUFAs In The Ancestral Picoalga Ostreococcus tauri

Eukaryotic {Delta}6-desaturases are microsomal enzymes which balance the synthesis of {omega}-3 and {omega}-6 C18-polyunsaturated-fatty-acids (PUFA) accordingly to their specificity. In several microalgae, including O. tauri, plastidic C18-PUFA are specifically regulated by environmental cues suggesting an autonomous control of {Delta}6-desaturation of plastidic PUFA. Sequence retrieval from O. tauri desaturases, highlighted two putative {Delta}6/{Delta}8-desaturases sequences clustering, with other microalgal homologs, apart from other characterized {Delta}-6 desaturases. Their overexpression in heterologous hosts, including N. benthamiana and Synechocystis, unveiled their {Delta}6-desaturation activity and plastid localization. O. tauri lines overexpressing these {Delta}6-desaturases no longer adjusted their plastidic C18-PUFA amount under phosphate starvation but didnt show any obvious physiological alterations. Detailed lipid analyses from the various overexpressing hosts, unravelled that the substrate features involved in the {Delta}6-desaturase specificity importantly involved the lipid head-group and likely the non-substrate acyl-chain, in addition to the overall preference for the {omega}-class of the substrate acyl-chain. The most active desaturase displayed a broad range substrate specificity for plastidic lipids and a preference for {omega}-3 substrates, while the other was selective for {omega}-6 substrates, phosphatidylglycerol and 16:4-galactolipid species specific to the native host. The distribution of plastidial {Delta}6-desaturase products in eukaryotic hosts suggested the occurrence of C18-PUFA export from the plastid. One sentence summaryOsteococcus tauri plastidic lipid C18-PUFA remodelling involves two plastid-located cytochrome-b5 fused {Delta}6-desaturases with distinct preferences for both head-group and acyl-chain.

biochemistry↗

bioRxiv2018

A stress-response-related inter-compartmental signalling pathway regulates embryonic cuticle integrity in Arabidopsis

The embryonic cuticle is necessary for normal seed development and seedling establishment in Arabidopsis. Although mutants with defective embryonic cuticles have been identified, neither the deposition of cuticle material, nor its regulation, has been described during embryogenesis. Here we use electron microscopy, lipid staining and permeability assays to show that cuticle deposition initiates de novo in patches on globular embryos. By combining these techniques with genetics and gene expression analysis, we show that successful patch coalescence to form a continuous cuticle requires a signalling involving the endosperm-specific subtilisin protease ALE1 and the receptor kinases GSO1 and GSO2, which are expressed in the developing embryonic epidermis. Transcriptome analysis shows that this pathway regulates stress-related gene expression in seeds. Consistent with these findings we show genetically, and through activity analysis, that the stress-associated MPK6 protein acts downstream of GSO1 and GSO2 in the developing embryo. We propose that a stress-related signalling pathway has been hijacked in some angiosperm seeds through the recruitment of endosperm-specific components. Our work reveals the presence of an inter-compartmental dialogue between the endosperm and embryo that ensures the formation of an intact and functional cuticle around the developing embryo through an \"auto-immune\" type interaction.

plant biology↗