Читать книгу Biotechnology of Fruit and Nut Crops - Группа авторов - Страница 134

Tranbarger et al. (2011) examined the transcriptional basis of metabolic characters in the oil palm mesocarp. Morphological, cellular, biochemical and hormonal features defined key phases of mesocarp development. A 454 pyrosequencing-derived transcriptome was assembled for the developmental phases preceding and during maturation and ripening, when high rates of lipid and carotenoid biosynthesis occur. A contig similar to the A. thaliana seed oil transcription factor WRINKLED1 was identified with a transcript profile coordinated with those of several fatty acid biosynthetic genes and the high rates of lipid accumulation, suggesting some common regulatory features between seeds and fruits. This result was confirmed by Bourgis et al. (2011).

The oil palm provides an original model for examining ripening processes and regulation. Histochemical analysis and cell parameter measurements have revealed cell wall and middle lamella expansion and degradation during ripening and in response to ethylene (Tranbarger et al., 2017). Cell wall-related transcript profiles suggest a transition from synthesis to degradation is under transcriptional control during ripening, in particular a switch from cellulose, hemicellulose and pectin synthesis to hydrolysis and degradation. The data provide evidence for the transcriptional activation of expansin, polygalacturonase, mannosidase, β-galactosidase, and xyloglucan endotransglucosylase/hydrolase proteins in the ripening oil palm mesocarp, suggesting widespread conservation of these activities during ripening for monocotyledonous and eudicotyledonous fruit types. Profiling of the most abundant oil palm polygalacturonase (EgPG4) and 1-aminocyclopropane-1-carboxylic acid oxidase (ACO) transcripts during development and in response to ethylene demonstrated both are sensitive markers of ethylene production and inducible gene expression during mesocarp ripening and provides evidence for a conserved regulatory module between ethylene and cell wall pectin degradation. A comprehensive analysis of NAC transcription factors confirmed at least ten transcripts from diverse NAC domain clades are expressed in the mesocarp during ripening, four of which are induced by ethylene treatment, with the two most inducible, EgNAC6 and EgNAC7, phylogenetically similar to the tomato NAC-NOR master-ripening regulator. Overall, the study from Tranbarger et al. (2017) provides evidence that despite the phylogenetic distance of the oil palm within the family Arecaceae from the most extensively studied monocot, i.e. banana, it appears that ripening mechanisms of divergent monocot and eudicot fruit lineages are regulated by evolutionarily conserved molecular physiological processes.