RESUMEN
Starch is a biologically and commercially important polymer of glucose. Starch is organized into starch grains (SGs) inside amyloplasts. The SG size differs depending on the plant species and is one of the most important factors for industrial applications of starch. There is limited information on genetic factors regulating SG sizes. In this study, we report the rice (Oryza sativa) mutant substandard starch grain6 (ssg6), which develops enlarged SGs in endosperm. Enlarged SGs are observed starting at 3 d after flowering. During endosperm development, a number of smaller SGs appear and coexist with enlarged SGs in the same cells. The ssg6 mutation also affects SG morphologies in pollen. The SSG6 gene was identified by map-based cloning and microarray analysis. SSG6 encodes a protein homologous to aminotransferase. SSG6 differs from other rice homologs in that it has a transmembrane domain. SSG6-green fluorescent protein is localized in the amyloplast membrane surrounding SGs in rice endosperm, pollen, and pericarp. The results of this study suggest that SSG6 is a novel protein that controls SG size. SSG6 will be a useful molecular tool for future starch breeding and applications.
Asunto(s)
Endospermo/metabolismo , Proteínas de la Membrana/metabolismo , Oryza/metabolismo , Proteínas de Plantas/metabolismo , Plastidios/metabolismo , Almidón/metabolismo , Transaminasas/metabolismo , Secuencia de Aminoácidos , Secuencia de Bases , Gránulos Citoplasmáticos/genética , Gránulos Citoplasmáticos/metabolismo , Endospermo/genética , Regulación de la Expresión Génica de las Plantas , Proteínas Fluorescentes Verdes/genética , Proteínas Fluorescentes Verdes/metabolismo , Immunoblotting , Membranas Intracelulares/metabolismo , Proteínas de la Membrana/genética , Microscopía Confocal , Microscopía Electrónica de Transmisión , Mutación , Análisis de Secuencia por Matrices de Oligonucleótidos , Oryza/genética , Proteínas de Plantas/genética , Plastidios/genética , Plastidios/ultraestructura , Polen/genética , Polen/metabolismo , Homología de Secuencia de Aminoácido , Transaminasas/genéticaRESUMEN
Human (h)Langerin/CD207 is a C-type lectin of Langerhans cells (LC) that induces the formation of Birbeck granules (BG). In this study, we have cloned a cDNA-encoding mouse (m)Langerin. The predicted protein is 66% homologous to hLangerin with conservation of its particular features. The organization of human and mouse Langerin genes are similar, consisting of six exons, three of which encode the carbohydrate recognition domain. The mLangerin gene maps to chromosome 6D, syntenic to the human gene on chromosome 2p13. mLangerin protein, detected by a mAb as a 48-kDa species, is abundant in epidermal LC in situ and is down-regulated upon culture. A subset of cells also expresses mLangerin in bone marrow cultures supplemented with TGF-beta. Notably, dendritic cells in thymic medulla are mLangerin-positive. By contrast, only scattered cells express mLangerin in lymph nodes and spleen. mLangerin mRNA is also detected in some nonlymphoid tissues (e.g., lung, liver, and heart). Similarly to hLangerin, a network of BG form upon transfection of mLangerin cDNA into fibroblasts. Interestingly, substitution of a conserved residue (Phe(244) to Leu) within the carbohydrate recognition domain transforms the BG in transfectant cells into structures resembling cored tubules, previously described in mouse LC. Our findings should facilitate further characterization of mouse LC, and provide insight into a plasticity of dendritic cell organelles which may have important functional consequences.