Unveiling DIR proteins involved in cork formation: insights from transcriptome analysis and cis-element co-occurrence

Abstract Cork, extracted sustainably from cork oak ( Quercus suber ), plays a pivotal role in various ecological, social, and economic aspects of Mediterranean regions. Influenced by genetic and environmental factors, the genetic control of cork production remains poorly understood. This study delves into the involvement of dirigent proteins (DIR) in cork lignification and explores potential regulatory mechanisms underlying the distinct thickness and porosity of cork produced by different trees. Transcriptomic analyses of phellogen, the meristematic cells that will give origin to cork, pointed to possible co-expression patterns of dirigent proteins (DIR), peroxidases (PRX), and laccases (LAC) that may shape cork characteristics. Our phylogenetic approach distinguishes cork-associated DIR from those engaged in lignan synthesis and highlights QsDIR_LOC112039424, that possess an endodermal domain akin to DIR proteins from Arabidopsis involved in the Casparian strip lignification. Additionally, promoter analysis identifies at the same position, −300 base pairs, a putative cis -element shared by QsDIR_LOC112039424, QsPRX_LOC112006708 and QsLAC_LOC112039867, that is recognised by MYB62 transcription factors. Requiring further validation, these findings offer insights on potential regulatory hubs controlling the phellogen activity and impacting the thickness and porosity of the resulting corks.