High-order mutants reveal an essential requirement for peroxidases but not laccases in Casparian strip lignification

Abstract

The invention of lignin has been at the heart of plants' capacity to colonize land, allowing them to grow tall, transport water within their bodies and protect themselves against various stresses.Consequently, this polyphenolic polymer, that impregnates the cellulosic plant cell walls, now represents the second most abundant polymer on Earth, after cellulose itself. Yet, despite its great physiological, ecological and economical importance, our knowledge of lignin biosynthesis in vivo, especially the crucial last steps of polymerization within the cell wall, remains vague. Specifically, the respective roles and importance of the two main polymerizing enzymes classes, laccases and peroxidases have remained obscure. One reason for this lies in

Phellem translational landscape throughout secondary development inArabidopsisroots

“…S5a ). Peroxidases are described in lignin polymerization (Francoz et al, 2015; Rojas-murcia et al, 2020) and it was hypothesized that such proteins could be also involved in the cross-linking of suberin phenolic monomers to the cell wall components (Bernards et al, 1999; Bernards et al, 2004). In fact several peroxidases are commonly found in the phellem of other plant species (Alonso-Serra et al, 2019; Lopes et al, 2019; Vulavala et al, 2019; Rains et al, 2018; Boher et al, 2018).…”

Highlighting reactive oxygen species as multitaskers in root development

“…In fact, the CS was devoid in the quintuple mutant prx03 prx09 prx39 prx72 prx64 , while it showed no difference in the lac1 3 5 7 8 9 12 13 16 nonuple mutant compared with the WT. Together, these findings suggest that PRXs play very specific roles in various contexts, and LACs are redundant for lignification of primary cell walls but are required for lignification of secondary cell walls ( Rojas-Murcia et al, 2020 ). Additionally, other RBOH and PRX enzymes are also known to be involved in ROS homeostasis and cell wall remodeling in the endodermis, including apoplastic RBOHD, PRX37, and PRX72.…”

“…It has been observed that PRX72 expression is increased in the lac4 lac11 lac17 triple mutants, implying a possible functional linkage between PRXs and LACs during monolignol coupling ( Zhao et al, 2013 ). However, increased PRX72 expression is not sufficient to rescue the lignin defect in the triple mutant, indicating that LACs and PRXs can still have distinct or complementary roles during monolignol assembly ( Rojas-Murcia et al, 2020 ). Moreover, PRX17 is also involved in lignified tissue formation ( Figure 2 ) and, more precisely, in regulating the kinetics of lignified wall formation ( Herrero et al, 2013 ; Hoffmann et al, 2020 ).…”

“…Apart from PRXs, MYB36 may also target the endodermis-enriched LACs. LACs are glycosylated, multi-copper enzymes that catalyze the oxidation of various phenolic substrates using O 2 as final electron acceptor, not requiring H 2 O 2 ( Rojas-Murcia et al, 2020 ). Previously, the role of LACs in lignification in the vascular tissue was reported as the overall lignin content was reduced in both lac and prx mutants ( Pfister et al, 2014 ; von Wangenheim et al, 2017 ; Wunderling et al, 2018 ).…”

“…Previously, the role of LACs in lignification in the vascular tissue was reported as the overall lignin content was reduced in both lac and prx mutants ( Pfister et al, 2014 ; von Wangenheim et al, 2017 ; Wunderling et al, 2018 ). However, the role of LACs in the endodermis and whether some cell types preferentially use LACs and others PRXs were addressed recently ( Rojas-Murcia et al, 2020 ). In fact, the CS was devoid in the quintuple mutant prx03 prx09 prx39 prx72 prx64 , while it showed no difference in the lac1 3 5 7 8 9 12 13 16 nonuple mutant compared with the WT.…”