Translational profile of developing phellem cells in Arabidopsis thaliana roots

Abstract

The phellem is a specialized boundary tissue providing the first line of defense against abiotic and biotic stresses in organs undergoing secondary growth. Phellem cells undergo several differentiation steps, which include cell wall suberization, cell expansion, and programmed cell death. Yet, the molecular players acting particularly in phellem cell differentiation remain poorly described, particularly in the widely used model plant Arabidopsis thaliana. Using specific marker lines we followed the onset and progression of phellem differentiation in A. thaliana roots and further targeted the translatome of newly developed phellem cells using translating ribosome affinity purification followed by mRNA sequencing (TRAP-SEQ). We showed that phellem suberization is initiated early after phellogen (cork cambium) division. The specific translational landscape was organized in three main domains related to energy production, synthesis and transport of cell wall components, and response to stimulus. Novel players in phellem differentiation related to suberin monomer transport and assembly as well as novel transcription regulators were identified. This strategy provided an unprecedented resolution of the translatome of developing phellem cells, giving a detailed and specific view on the molecular mechanisms acting on cell differentiation in periderm tissues of the model plant Arabidopsis.

The Combined Effect of Heat and Osmotic Stress on Suberization of Arabidopsis Roots

“…Combination of heat and osmotic stress (H+O) was imposed to Arabidopsis plants at 8 DAG, on the onset of root secondary development [ 31 ]. In order to evaluate the effect of combined stress on root suberization, we performed a morphological and spatio-temporal characterization of root suberization, targeting the expression of the suberin biosynthesis marker Glycerol-3-phosphate acyltransferase 5-GPAT5 (pGPAT5:mCITRINE-SYP122 [ 30 ], as well as cell-wall suberization, using FY staining [ 36 ]).…”

“…In this work, we used 8 DAG Arabidopsis to study the influence of a combination of heat and osmotic stress on root suberization. At 8 DAG, Arabidopsis root system is already complex, with secondary development present in a small portion of the upper part of the main root, with suberized phellem as the outermost layer [ 31 ], and below this region, in primary development, the main root has a layer of suberized endodermis around the stele. In addition, LRs are already present, showing equivalent morphology of younger roots, both undergoing primary development.…”

“…Interestingly, the phytohormone abscisic acid (ABA), the main signaling hormone detected in heat and drought response [ 5 , 29 ], is also described as the main transcriptional activator of suberin biosynthesis genes [ 30 , 31 ]. By mimicking the abiotic stress stimulus [ 29 ], ABA application induces suberin biosynthesis genes, endodermis suberization as well as ectopic deposition of suberin in cells that normally do not suberize [ 30 , 32 ].…”

“…In this work, we aimed to clarify how Arabidopsis root suberization is modulated by combined drought and heat stress by targeting the roots at the onset of secondary development. At this stage, the Arabidopsis main root displays a gradient of development, from primary (closer to root tip) to secondary growth (below the hypocotyl) [ 31 , 33 ], with two distinct suberized tissues: the endodermis, in the region of primary development, and the phellem (the outermost layer), in the region of secondary development. Suberized endodermis plays a role as transport barrier to the stele, while phellem is mostly a protective layer.…”

Cork Development: What Lies Within

“…Recently, Lopes et al, (2019) identified CYP82D , CYP76A and CYP705A in phellogen samples. When Arabidopsis root phellem was studied for suberin synthesis, it was possible to detect the expression of suberin synthesis components; CYP86A1 , CYP86B1 , FAR1/4/5 , GTPAT5/7 , FACT , and ASFT [ 74 ] indicating a conservative mechanism for suberin biosynthesis.…”