Regulation of secondary cell wall lignification by abiotic and biotic constraints

The appearance of lignin, 400 million-years ago, has been crucial for the successful land colonization by plants. This complex phenolic polymer which confers hydrophobicity and resistance to degradation to secondary cell walls, is also neosynthesized in response to both biotic and abiotic stresses. Lignin biosynthesis during development is regulated by a complex hierarchical transcriptional gene regulatory network. Notably, distinct abiotic stresses can co-opt different genes of this network, leading to different lignification patterns. Co-optation of this developmental network is a mean to facilitate adaptation to stress by promoting functional adaptation. Supporting this hypothesis, a growing number of transcription factors known to be involved in the regulation of secondary cell wall, were shown to integrate both developmental and environmental signals leading to an increased tolerance to abiotic stresses, such as drought or salinity. On the other hand, some transcription factors known to be involved in stress response were shown to impact lignin biosynthesis as part of the functional adaptation performed by plants to cope with natural constraints. In this review, we focus on the most recent findings on the cross-talk between stress-signaling pathways and regulation of lignin biosynthesis in response to abiotic stress and to a lesser extent to biotic stresses. We consider the transcriptional regulation level which has received much attention and the emerging roles of posttranscriptional and posttranslational regulations in the control of lignin biosynthesis in response to stresses. We end discussing future outlines and challenges to fill gaps in this emerging and exciting research field.