Implication of the suberin pathway in adaptation to waterlogging and hypertrophied lenticels formation in pedunculate oak (Quercus robur L.)

Waterlogging causes stressful conditions for perennial species. The temporary overabundance of water in waterlogged soil can induce hypoxia in the rhizosphere, leading to root death, tree decline and even dieback. Two closely related members of the European white oak complex, pedunculate (Quercus robur L.) and sessile (Quercus petraea Matt. Liebl.) oaks, have different ecological characteristics, especially regarding their adaptation to soil waterlogging. The tolerance of waterlogging observed in pedunculate oak is driven principally by its ability to produce adaptive structures, hypertrophied lenticels and adventitious roots, and to switch rapidly its metabolism to the fermentative pathway. This study had two objectives: (i) to identify genes important for adaptation to waterlogging and (ii) to gain insight into the molecular mechanisms involved in hypertrophied lenticel formation in pedunculate oak. We subjected seedlings of the two species to hypoxia by maintaining the water level 2 cm above the collar. The immersed part of the stem (i.e., containing hypertrophied lenticels in pedunculate oak) was sampled after 9 days of waterlogging stress and its gene expression was investigated by RNA-seq. Genes displaying differential expression between the two species were identified with the DESeq R package and a false discovery rate of 0.001. We found that 3705 contigs were differentially regulated between the two species. Twenty-two differentially expressed genes were validated by real-time quantitative polymerase chain reaction. The suberin biosynthesis pathway was found to be upregulated in pedunculate oak, consistent with molecular mechanisms analogous to those operating in the radial oxygen loss barrier in waterlogging-tolerant species.