Expression of DNA methyltransferases is involved in Quercus suber cork quality

Abstract

Cork oak (Quercus suber ) is an important Portuguese species, mainly due to the economic value of the cork it produces. Cork results from phellogen, a meristematic tissue, which can locally produce lenticels or have discontinuities, originating "defects": pores and nail inclusions that are detrimental to cork industrial use. Epigenetic processes control plant development and its deregulation can lead to altered phenotypes; therefore, the study of epigenetic players in the phellogen is important to understand the emergence of cork's defects. DNA methyltransferases (DNMTs) and one protein associated to MET1 (DMAP1) were characterized in Q. suber, and their gene expression was analyzed in phellogen and contiguous differentiating cell layers of trees producing high and low quality cork, after the evaluation of their defects by physical and image analysis methods. All classes of DNMTs (MET, DRM, and CMT) with the respective canonical motifs were identified in Q. suber. The expression analyses of these genes showed that QsDRM2 was the most active methyltransferases in the cells analyzed, and that all the genes were differentially expressed in trees with distinct cork quality, with a tendency for higher expression levels in low quality producers. Interestingly, the global methylation level was higher in cells with low expression of DNA methyltransferases. A positive and significant correlation was obtained between QsDMAP1 gene expression and the percentage of cork defects. This work provides the first evidence that cork quality in Q. suber is likely influenced by epigenetic mechanisms.

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

“…These alterations accompanied by increased levels and a change in the distribution of DNA methylation in differentiating cork cells has also been observed in tapetum cells PCD correlating with an up-regulation of MET1 (Solís et al, 2014), responsible for CpG methylation maintenance in cycling cells (Huang et al, 2010). Indeed, QsMET1 was amongst the genes with higher levels of relative expression in the cork tissue contradicting, however, previous results in corks with different qualities (Ramos et al, 2013) where was argued that QsMET2 might be substituting QsMET1 function to maintain the CpG methylation during phellogen activity. In our work, although at lower levels than QsMET1 this gene was amongst the genes with the highest expression.…”

“…Another important process in meristematic derivative cells is the de novo methylation mainly accomplished by DRM1 and DMR2 through the RdDM pathway [reviewed in (Pikaard and Scheid, 2014)]. In differentiating cork cells where DNA methylation is increasing it was not surprising to find the highest levels of gene expression for QsDRM2 , according to previous results (Ramos et al, 2013). Different methyltransferases act together with chromatin remodeling complexes in an intricate interplay to modify chromatin structure and regulate transcription.…”

“…Primers were designed using Primer Premier 5.0 software (PREMIER Biosoft International, Palo Alto, CA, United States) except for QsDRM2 gene and housekeeping genes that was chosen from a previous gene expression studies in cork oak (Marum et al, 2012; Ramos et al, 2013). qRT-PCR experiments were performed in all tissues except for QsSUVH4 which were only performed in three-year-old sprigs and traumatic periderms.…”

Differential DNA Methylation Patterns Are Related to Phellogen Origin and Quality of Quercus suber Cork

“…Amadia cork thickness was measured according to Ramos et al . [39]. Image acquisition of the two radial, two transversal and one tangential sections was made through scanning at a minimum resolution of 300 dpi.…”

“…Although the genus Quercus has already two sequenced genomes [36,37] no genomic data was available for cork oak. Some studies have been targeting cytosine methylation in this species [38–40] evidencing its association with cork quality, namely on cork tissue homogeneity [39]. …”