RESUMEN
Lignin is a major component of plant cell walls that is essential to their function. However, the strong bonds that bind the various subunits of lignin, and its cross-linking with other plant cell wall polymers, make it one of the most important factors in the recalcitrance of plant cell walls against polysaccharide utilization. Plants make lignin from a variety of monolignols including p-coumaryl, coniferyl, and sinapyl alcohols to produce the three primary lignin units: p-hydroxyphenyl, guaiacyl, and syringyl, respectively, when incorporated into the lignin polymer. In grasses, these monolignols can be enzymatically preacylated by p-coumarates prior to their incorporation into lignin, and these monolignol conjugates can also be "monomer" precursors of lignin. Although monolignol p-coumarate-derived units may comprise up to 40% of the lignin in some grass tissues, the p-coumarate moiety from such conjugates does not enter into the radical coupling (polymerization) reactions of lignification. With a greater understanding of monolignol p-coumarate conjugates, grass lignins could be engineered to contain fewer pendent p-coumarate groups and more monolignol conjugates that improve lignin cleavage. We have cloned and expressed an enzyme from rice that has p-coumarate monolignol transferase activity and determined its kinetic parameters.
Asunto(s)
Aciltransferasas/química , Ácidos Cumáricos/química , Lignina/química , Oryza/enzimología , Proteínas de Plantas/química , Acetilación , Aciltransferasas/genética , Aciltransferasas/metabolismo , Clonación Molecular , Ácidos Cumáricos/metabolismo , Expresión Génica , Cinética , Lignina/biosíntesis , Lignina/genética , Oryza/genética , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Propionatos , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismoRESUMEN
Plant cell walls are complex structures that offer structural and mechanical support to plant cells and are ultimately responsible for plant architecture and form. Pectins are a large group of complex polysaccharides of the plant cell wall that are made in the Golgi and secreted to the wall. The methylesterification of pectins is believed to be an important factor for the dynamic properties of the cell wall. Here, we report on a protein of unknown function discovered using an extensive proteomics analysis of cotton Golgi. Through bioinformatic analyses, we identified the ortholog of such protein, here named cotton Golgi-related 3 (CGR3) in Arabidopsis and found that it shares conserved residues with S-adenosylmethionine methyltransferases. We established that CGR3 is localized at the Golgi apparatus and that the expression of the CGR3 gene is correlated with that of several cell wall biosynthetic genes, suggesting a possible role of the protein in pectin modifications. Consistent with this hypothesis, immunofluorescence microscopy with antibodies for homogalacturonan pectins (HG) indicated that the cell walls of cgr3 knockout mutants and plants overexpressing CGR3 are decreased and increased in HG methylesterification, respectively. Our results suggest that CGR3 plays a role in the methylesterification of homogalacturonan in Arabidopsis.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Aparato de Golgi/metabolismo , Pectinas/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Pared Celular/genética , Pared Celular/metabolismo , Clonación Molecular , Esterificación , Aparato de Golgi/genética , Datos de Secuencia Molecular , Transporte de ProteínasRESUMEN
The surface uplift of mountain belts is generally assumed to reflect progressive shortening and crustal thickening, leading to their gradual rise. Recent studies of the Andes indicate that their elevation remained relatively stable for long periods (tens of millions of years), separated by rapid (1 to 4 million years) changes of 1.5 kilometers or more. Periodic punctuated surface uplift of mountain belts probably reflects the rapid removal of unstable, dense lower lithosphere after long-term thickening of the crust and lithospheric mantle.