Novel cassava starches with low and high amylose contents: Structural and macro-molecular characterization in comparison with other commercial sources

Cassava (Manihot esculenta Crantz) is one of the most important sources of commercial production of starch along with potato, maize and wheat particularly for tropical and subtropical regions of the world. It is the third most important source of calories in tropics, after rice and maize. Natural mutation, and induced ones in cassava starch have recently been reported leading to new starches with low and high-amylose contents (0 and 30-31 %). These mutants are drastically different from normal cassava starch whose amylose content typically ranges between 15-25 %. The aims of this study were to have an overview of the structural variability among the recently discovered cassava mutants comparatively to normal and amylose-free potato and maize starches. The macromolecular features, the crystallinity, the granule sizes, and the thermal properties of these new mutants were compared with five normal cassava starches (ranging from 16.8 to 21.5 % amylose) and commercial versions of amylose-free or normal potato and maize starch. The structure of cassava amylopectin was not modified by the waxy mutation and waxy cassava starch exhibited properties similar to the ones of waxy maize starch. Waxy cassava and maize amylopectins show similar molar masses and radii of gyration (from 408×106 g mol-1 to 520×106 g mol-1; and from 277 to 285 nm, respectively). Waxy potato amylopectin exhibit lower molar mass and size. Inversely, the higher-amylose mutations induced by gamma rays radiation in cassava, modified deeply the branching pattern of amylopectin as well as the starch characteristics and properties: molar masses and radii of gyration decreased, while branching degree increased. These modifications resulted in changes in starch granule ultrastructure (lowered starch crystallinity), a weak organized structure, and increased susceptibility to mild acid hydrolysis. The distinctive properties of the new cassava starches demonstrated in this article suggest new opportunities and commercial applications for these tropical sources of starch. (Résumé d'auteur

ttl mutants are impaired in cellulose biosynthesis under osmotic stress

As sessile organisms, plants require mechanisms to sense and respond to the challenging environment, that encompass both biotic and abiotic factors that results in differential development. In these conditions is essential to balance growth and stress responses. As cell walls shape plant growth, this differential growth response cause alterations to the plant cell wall and cellulose is a major component. Therefore, understanding the mechanisms that regulate cellulose biosynthesis is essential to develop strategies to improve plant production. Previous studies have shown that the GSK3 kinase BIN2 modulate cellulose biosynthesis through phosphorylating cellulose synthases and that the expression of cellulose synthases are regulated by Brassinosteroids. Our previous work reveals that the tetratricopeptide-repeat thioreoxin-like (TTL) TTL1, TTL3, and TTL4 genes, in addition to their reported role in abiotic stress tolerance, are positive regulators of BR signaling. We observe association of TTL3 with most core components in traducing BR signalling, such as LRR-RLK BRI1, BIN2 and the transcription factor BES1 that positively regulate cellulose biosynthesis. We show that ttl mutants are affected in cellulose biosynthesis, particularly in osmotic stress conditions. Furthermore, TTL3 associates with LRR-RLKs that have been shown to be important for cellulose biosynthesis such as FEI1 in the FEI1/FEI2/SOS5 pathway. We aim to investigate the mechanisms by which TTL proteins regulate cellulose biosynthesis using a combination of genetics, biochemical, and molecular and cell biology approaches. This work was supported by grants from: (1) Ministerio de Ciencia e Innovación BIO2014-55380-R, BIO2014-56153-REDT; (2) Ministerio de Economía, Industria y Competitividad (BES-2015-071256); (3) Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech.This work was supported by grants from: (1) Ministerio de Ciencia e Innovación BIO2014-55380-R, BIO2014-56153-REDT; (2) Ministerio de Economía, Industria y Competitividad (BES-2015-071256); (3) Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Tyrosine phosphorylation controls brassinosteroid receptor activation by triggering membrane release of its kinase inhibitor

Receptor tyrosine kinases control many critical processes in metazoans, but these enzymes appear to be absent in plants. Recently, two Arabidopsis receptor kinases-BRASSINOSTEROID INSENSITIVE 1 (BRI1) and BRI1-ASSOCIATED KINASE1 (BAK1), the receptor and coreceptor for brassinosteroids-were shown to autophosphorylate on tyrosines. However, the cellular roles for tyrosine phosphorylation in plants remain poorly understood. Here, we report that the BRI1 KINASE INHIBITOR 1 (BKI1) is tyrosine phosphorylated in response to brassinosteroid perception. Phosphorylation occurs within a reiterated [KR][KR] membrane targeting motif, releasing BKI1 into the cytosol and enabling formation of an active signaling complex. Our work reveals that tyrosine phosphorylation is a conserved mechanism controlling protein localization in all higher organisms

Unraveling the mechanism of TTL genes in cellulose biosynthesis

As sessile organisms, plants require mechanisms to sense and respond to the challenging environment, that encompass both biotic and abiotic factors that results in differential development. In these conditions is essential to balance growth and stress responses. As cell walls shape plant growth, this differential growth response cause alterations to the plant cell wall where cellulose is the major component. Therefore, understanding the mechanisms that regulate cellulose biosynthesis is essential to develop strategies to improve plant production. In Arabidopsis, the TETRATRICOPEPTIDE THIOREDOXIN-LIKE (TTL) gene family is composed by four members (TTL1 to TTL4) and mutations in TTL1, TTL3, and TTL4 genes cause reduced growth under salt and osmotic stress due to defects in plant cell wall integrity. We observe association of TTL3 with most core components in traducing BR signalling, such as LRR-RLK BRI1 or GSK3 BIN2 that modulate cellulose biosynthesis through phosphorylating cellulose synthases. Here, we show that ttl mutants present defects in the plant cell wall, particularly in Isoxaben, salt or sucrose stress. Spinning disk microscopy in etiolated hypocotyls reveals that, TTL proteins are responsible for the cellulose synthase complex (CSC) stability in plasma membrane (PM) upon sucrose stress. Moreover, TTL3 associates with LRR-RLKs that have been shown to be important for cellulose biosynthesis such as FEI1 in the FEI1/FEI2/SOS5 pathway. We aim to investigate the mechanisms by which TTL proteins regulate CesA stability in PM under stress, using a combination of genetics, biochemical, and molecular and cell biology approaches.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. This work was supported by grants from: (1) Ministerio de Ciencia e Innovación BIO2014-55380-R, BIO2014-56153-REDT; (2) Ministerio de Economía, Industria y Competitividad (BES-2015-071256

Dual role for ubiquitin in plant steroid hormone receptor endocytosis

Brassinosteroids are plant steroid hormones that control many aspects of plant growth and development, and are perceived at the cell surface by the plasma membrane-localized receptor kinase BRI1. Here we show that BRI1 is post-translationally modified by K63 polyubiquitin chains in vivo. Using both artificial ubiquitination of BRI1 and generation of an ubiquitination-defective BRI1 mutant form, we demonstrate that ubiquitination promotes BRI1 internalization from the cell surface and is essential for its recognition at the trans-Golgi network/early endosomes (TGN/EE) for vacuolar targeting. Finally, we demonstrate that the control of BRI1 protein dynamics by ubiquitination is an important control mechanism for brassinosteroid responses in plants. Altogether, our results identify ubiquitination and K63-linked polyubiquitin chain formation as a dual targeting signal for BRI1 internalization and sorting along the endocytic pathway, and highlight its role in hormonally controlled plant development

Les lacs d’Hanoï, quelle place pour une pièce urbaine endémique ?

La ville de Hanoï s’est établie au sein d’un réseau hydrographique complexe : la plaine du delta du fleuve Rouge, un entremêlement de rivières offrant voies de communication et remparts naturels. Ce réseau s’est complexifié́ avec sa domestication par l’homme : un système de digues protégeant les villes des crues des fleuves, et la constitution de nombreux lacs et cours d’eau pour temporiser et d’évacuer les pluies. Ces lacs jouent un rôle important, à la fois technique, en luttant contre les risques d’inondation, mais aussi culturel, en déterminant l’emplacement de la ville et de nombreux édifices spirituels. À ces deux fonctions s’ajoute, au début du xxe siècle, celle de l’espace public : leurs réaménagements sont planifiés à l’échelle de la ville, pour en faire de véritables parcs et jardins créés durant la période coloniale, ou aménagés après l’indépendance. À partir des années 1992, avec le développement intense de l’urbanisation de la capitale, la qualité de ces lacs se dégrade. Ceux-ci deviennent parfois un obstacle, et sont asséchés par la construction de nouvelles infrastructures de transport, ou la réalisation de grandes opérations immobilières… Seuls les principaux lacs du centre-ville sont préservés. Les autres, plus modestes, sont grignotés. Face aux enjeux contemporains, les lacs ont pourtant un rôle et un potentiel remarquable. Corridors écologiques à l’échelle de la ville, espaces publics de proximité dans un îlot dense d’habitations, ils sont primordiaux pour pérenniser l’infiltration de la nature en ville et la conservation d’espaces continus de verdure, permettant de lutter plus durablement contre les effets de microclimat urbain, et d’îlots de chaleur. Ils doivent être intégrés et mieux pris en compte dans les réflexions urbaines, et représenter un véritable angle d’approche pour l’aménagement de la ville et de quartiers.The city of Hanoi was established within the complex hydrographic network of the Red River Delta plain, a web of rivers providing transport routes and natural boundaries. This network became more complex with its domestication: a system of dikes protecting built-up areas from river floods and the creation of many lakes and rivers to delay and evacuate rainfall runoff. These lakes play an important role technically against flood risks and culturally in determining the location of the city as well as that of many religious buildings. In addition to these two functions the lakes started to play a role as public spaces in the beginning of the 20th century with their redevelopment which was planned throughout the city. Some of them were included in the development of city parks and gardens during the colonial period and others were developed after the country’s independence. From 1992, with the intense urbanization of the capital the quality of these lakes deteriorated. If they presented obstacles, they were dried up to make way for new transport infrastructures or to enable the completion of major real estate operations. Only the main lakes in the city centre were preserved. Others smaller lakes were gradually encroached upon. Faced with contemporary challenges, however, these lakes play a remarkable role and have great potential. As ecological corridors for the city and local public spaces within a dense residential area they are essential in sustaining the infiltration of nature within the city and the conservation of uninterrupted green spaces, making it possible to fight more sustainably against the effects of urban micro-climates and heat islands. There is a need to take them into account and better integrate them within local and city-wide urban planning and development projects

Trafficking modulator TENin1 inhibits endocytosis, causes endomembrane protein accumulation at the pre-vacuolar compartment and impairs gravitropic response in Arabidopsis thaliana

Auxin gradients are established and maintained by polarized distribution of auxin transporters that undergo constitutive endocytic recycling from the PM (plasma membrane) and are essential for the gravitropic response in plants. The present study characterizes an inhibitor of endomembrane protein trafficking, TE1 (trafficking and endocytosis inhibitor 1/TENin1) that reduces gravitropic root bending in Arabidopsis thaliana seedlings. Short-term TE1 treatment causes accumulation of PM proteins, including the BR (brassinosteroid) receptor BRI1 (BR insensitive 1), PIP2a (PM intrinsic protein 2a) and the auxin transporter PIN2 (PIN-FORMED 2) in a PVC (pre-vacuolar related compartment), which is sensitive to BFA (Brefeldin A). This compound inhibits endocytosis from the PM and promotes trafficking to the vacuole, consistent with inhibition of retrieval of proteins to the TGN (trans-Golgi network) from the PVC and the PM. However, trafficking of newly synthesized proteins to the PM is unaffected. The short-term protein trafficking inhibition and long-term effect on plant growth and survival caused by TE1 were fully reversible upon drug washout. Structure-activity relationship studies revealed that only minor modifications were possible without loss of biological activity. Diversity in Arabidopsis ecotypes was also exploited to identify two Arabidopsis accessions that display reduced sensitivity to TE1. This compound and the resistant Arabidopsis accessions may be used as a resource in future studies to better understand endomembrane trafficking in plants

The Arabidopsis protein phosphatase PP2C38 negatively regulates the central immune kinase BIK1

Plants recognize pathogen-associated molecular patterns (PAMPs) via cell surface-localized pattern recognition receptors (PRRs), leading to PRR-triggered immunity (PTI). The Arabidopsis cytoplasmic kinase BIK1 is a downstream substrate of several PRR complexes. How plant PTI is negatively regulated is not fully understood. Here, we identify the protein phosphatase PP2C38 as a negative regulator of BIK1 activity and BIK1-mediated immunity. PP2C38 dynamically associates with BIK1, as well as with the PRRs FLS2 and EFR, but not with the co-receptor BAK1. PP2C38 regulates PAMP-induced BIK1 phosphorylation and impairs the phosphorylation of the NADPH oxidase RBOHD by BIK1, leading to reduced oxidative burst and stomatal immunity. Upon PAMP perception, PP2C38 is phosphorylated on serine 77 and dissociates from the FLS2/EFR-BIK1 complexes, enabling full BIK1 activation. Together with our recent work on the control of BIK1 turnover, this study reveals another important regulatory mechanism of this central immune component

Resolving the homology-function relationship through comparative genomics of membrane-trafficking machinery and parasite cell biology

With advances in DNA sequencing technology, it is increasingly common and tractable to informatically look for genes of interest in the genomic databases of parasitic organisms and infer cellular states. Assignment of a putative gene function based on homology to functionally characterized genes in other organisms, though powerful, relies on the implicit assumption of functional homology, i.e. that orthology indicates conserved function. Eukaryotes reveal a dazzling array of cellular features and structural organization, suggesting a concomitant diversity in their underlying molecular machinery. Significantly, examples of novel functions for pre-existing or new paralogues are not uncommon. Do these examples undermine the basic assumption of functional homology, especially in parasitic protists, which are often highly derived? Here we examine the extent to which functional homology exists between organisms spanning the eukaryotic lineage. By comparing membrane trafficking proteins between parasitic protists and traditional model organisms, where direct functional evidence is available, we find that function is indeed largely conserved between orthologues, albeit with significant adaptation arising from the unique biological features within each lineage