A comparative transcriptomic approach to understanding the formation of cork

Abstract

Key message The transcriptome comparison of two oak species reveals possible candidates accounting for the exceptionally thick and pure cork oak phellem, such as those involved in secondary metabolism and phellogen activity. Abstract Cork oak, Quercus suber, differs from other Mediterranean oaks such as holm oak (Quercus ilex) by the thickness and organization of the external bark. While holm oak outer bark contains sequential periderms interspersed with dead secondary phloem (rhytidome), the cork oak outer bark only contains thick layers of phellem (cork rings) that accumulate until reaching a thickness that allows industrial uses. Here we compare the cork oak outer bark transcriptome with that of holm oak. Both transcriptomes present similitudes in their complexity, but whereas cork oak external bark is enriched with upregulated genes related to suberin, which is the main polymer responsible for the protective function of periderm, the upregulated categories of holm oak are enriched in abiotic stress and chromatin assembly. Concomitantly with the upregulation of suberin-related genes, there is also induction of regulatory and meristematic genes, whose predicted activities agree with the increased number of phellem layers found in the cork oak sample. Further transcript profiling among different cork oak tissues and conditions suggests that cork and wood share many regulatory mechanisms, probably reflecting similar ontogeny. Moreover, the analysis of transcripts accumulation during the cork growth season showed that most regulatory genes are upregulated early in the season when the cork cambium becomes active. Altogether our work provides the first transcriptome comparison between cork oak and holm oak outer bark, which unveils new regulatory candidate genes of phellem development.

Cork Oak Young and Traumatic Periderms Show PCD Typical Chromatin Patterns but Different Chromatin-Modifying Genes Expression

“…Also, in developing secondary xylem of Eucalyptus grandis , cell wall-related genes with vital roles in wood formation were found to be H3K4me3-enriched (Hussey et al, 2017). Considering that periderm formation involves cork cells expansion, cell wall suberization and deposition of waxes (Graça and Pereira, 2004; Pereira, 2007), we may speculate that genes involved in suberin and waxes synthesis and deposition, as well as cell death-associated genes are up-regulated in cork cells (Soler et al, 2007; Teixeira et al, 2017; Boher et al, 2018) through H3K4me3 modification. Tri-methylation of histone H3 at lysine 4 is imposed by ATXR3 and ATX3 (Berr et al, 2010; Guo et al, 2010; Chen et al, 2017), which level of expression relates well to the amount of H3K4me3 in young and traumatic periderms.…”

Tissue‐specific study across the stem reveals the chemistry and transcriptome dynamics of birch bark

“…The molecular regulation that takes place in the vascular cambium is well studied because of its direct effect on lignocellulosic biomass production (Etchells et al, 2015;Immanen et al, 2016;Sundell et al, 2017). By contrast, although bark anatomy and composition are well documented, and even some transcriptomes have been analyzed (Park et al, 2008;Mantello et al, 2014;Rosell et al, 2014;Celedon et al, 2017;Rains et al, 2017;Boher et al, 2018), bark development is still poorly understood at a molecular level. This is partially because not all tissues have been dissected and studied in the context of the whole stem, thus making it difficult to address tissue-specificity.…”

Developmental anatomy of anomalous structure and classification of commercial specifications and grades of the Astragalus membranaceus var. mongholicus

“…The root without rhytidome or “rotten heart” is of typical secondary structure of the dicotyledonous plant, which consists of periderm, secondary phloem, vascular cambium, and secondary xylem. Periderm is composed of three stratums, the phellem at the outer part, phellogen in the middle, and phelloderm at the inner side (Boher et al, ). There are 6–14 layers of phellem cells, and phelloderm consists of three to five layers of collenchymatous cells.…”