RESUMEN
Peroxidases have been shown to be involved in the polymerization of lignin precursors, but it remains unclear whether laccases (EC 1.10.3.2) participate in constitutive lignification. We addressed this issue by studying laccase T-DNA insertion mutants in Arabidopsis thaliana. We identified two genes, LAC4 and LAC17, which are strongly expressed in stems. LAC17 was mainly expressed in the interfascicular fibers, whereas LAC4 was expressed in vascular bundles and interfascicular fibers. We produced two double mutants by crossing the LAC17 (lac17) mutant with two LAC4 mutants (lac4-1 and lac4-2). The single and double mutants grew normally in greenhouse conditions. The single mutants had moderately low lignin levels, whereas the stems of lac4-1 lac17 and lac4-2 lac17 mutants had lignin contents that were 20 and 40% lower than those of the control, respectively. These lower lignin levels resulted in higher saccharification yields. Thioacidolysis revealed that disrupting LAC17 principally affected the deposition of G lignin units in the interfascicular fibers and that complementation of lac17 with LAC17 restored a normal lignin profile. This study provides evidence that both LAC4 and LAC17 contribute to the constitutive lignification of Arabidopsis stems and that LAC17 is involved in the deposition of G lignin units in fibers.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/genética , Lacasa/genética , Lignina/biosíntesis , Tallos de la Planta/metabolismo , Haz Vascular de Plantas/genética , Arabidopsis/enzimología , Arabidopsis/crecimiento & desarrollo , Proteínas de Arabidopsis/genética , Perfilación de la Expresión Génica , Regulación de la Expresión Génica de las Plantas , Prueba de Complementación Genética , Inflorescencia/genética , Inflorescencia/metabolismo , Lacasa/aislamiento & purificación , Lacasa/metabolismo , Lignina/análisis , Lignina/genética , Mutación , Tallos de la Planta/anatomía & histología , Tallos de la Planta/crecimiento & desarrollo , Haz Vascular de Plantas/enzimología , Plantas Modificadas Genéticamente , Regiones Promotoras GenéticasRESUMEN
BACKGROUND AND AIMS: Oil palm, an unbranched perennial monocotyledon, possesses a single shoot apical meristem (SAM), which is responsible for the initiation of the entire above-ground structure of the plant. To compare the palm SAM structure with those of other monocots and to study variations in its structure throughout the life of the plant, its organization was characterized from the embryonic stage to that of the reproductive plant. METHODS: SAM structure was studied by a combination of stained histological sections, light and confocal microscopy, and serial section-based three-dimensional reconstructions. KEY RESULTS: The oil palm SAM is characterized by two developmental phases: a juvenile phase with a single tunica-corpus structure displaying a gradual increase in size; and a mature phase characterized by a stable size, a modified shape and an established histological zonation pattern. In mature plants, fluctuations in SAM shape and volume occur, mainly as a consequence of changes in the central zone, possibly in relation to leaf initiation. CONCLUSIONS: Development of the oil palm SAM is characterized by a juvenile to mature phase transition accompanied by establishment of a zonal pattern and modified shape. SAM zonation is dynamic during the plastochron period and displays distinct features compared with other monocots.