Upon heat stress processing of ribosomal RNA precursors into mature rRNAs is compromised after cleavage at primary P site in Arabidopsis thalian a

Abstract

Transcription and processing of 45S rRNAs in the nucleolus are keystones of ribosome biogenesis. While these processes are severely impacted by stress conditions in multiple species, primarily upon heat exposure, we lack information about the molecular mechanisms allowing sessile organisms without a temperature-control system, like plants, to cope with such circumstances. We show that heat stress disturbs nucleolar structure, inhibits pre-rRNA processing and provokes imbalanced ribosome profiles in Arabidopsis thaliana plants. Notably, the accuracy of transcription initiation and cleavage at the primary P site in the 5’ETS (5’ External Transcribed Spacer) are not affected but the levels of primary 45S and 35S transcripts are, respectively, increased and reduced. In contrast, precursors of 18S, 5.8S and 25S RNAs are rapidly undetectable upon heat stress. Remarkably, nucleolar structure, pre-rRNAs from major ITS1 processing pathway and ribosome profiles are restored after returning to optimal conditions, shedding light on the extreme plasticity of nucleolar functions in plant cells. Further genetic and molecular analysis to identify molecular clues implicated in these nucleolar responses indicate that cleavage rate at P site and nucleolin protein expression can act as a checkpoint control towards a productive pre-rRNA processing pathway.

Arabidopsis DXO1 affects the processing of precursors of cytoplasmic and chloroplast ribosomal RNA

“…5B; probe P5, marked with an arrowhead). This species most likely corresponds to a stress-related P-C2 intermediate that was initially identified in irp7 mutants upon auxin treatment and represents a bypass pre-rRNA processing pathway called ‘ITS2-first’, in which the initial cleavage of the primary precursor occurs at site C2 within ITS2 (Palm et al ., 2019; Sáez-Vásquez and Delseny, 2019; Shanmugam et al ., 2021; Darriere et al ., 2022).…”

“…Accordingly, several Arabidopsis pre-rRNA processing mutants exhibit altered sensitivity to various stressors (e.g. irp (Palm et al ., 2019), apum23 (Huang et al ., 2018), apum24 (Maekawa et al ., 2018)) and the plant response to abiotic stresses includes altered expression of pre-rRNA processing factors and changes in the pre-rRNA maturation pathway (Palm et al ., 2019; Sáez-Vásquez and Delseny, 2019; Martinez-Seidel et al ., 2020; Shanmugam et al ., 2021; Darriere et al ., 2022). In response to stress, the expression of RP genes is regulated, inter alia, by the TOR signaling pathway (Petibon et al ., 2020).…”

“…Environmental stress, especially nutrient availability and heat, has been shown to alter pre-rRNA processing in Arabidopsis (Maekawa et al ., 2018; Shanmugam et al ., 2021; Darriere et al ., 2022). Indeed, in plants treated with elevated temperatures we observed changes in the accumulation of some rRNA precursors and detected an unusual P-C2 intermediate encompassing the 5.8S and 18S rRNAs.…”

“…Indeed, in plants treated with elevated temperatures we observed changes in the accumulation of some rRNA precursors and detected an unusual P-C2 intermediate encompassing the 5.8S and 18S rRNAs. These observations are consistent with recent studies on rRNA maturation under heat stress in plants, reporting an altered abundance of individual pre-rRNAs at low and/or high temperatures (Hang et al ., 2018; Liu et al ., 2020; Shanmugam et al ., 2021; Darriere et al ., 2022). These changes may reflect the influence of environmental temperature on plant ribosome biogenesis in natural habitats.…”

Nuclear dynamics: Formation of bodies and trafficking in plant nuclei

“…Plant nucleoli show speckled structures upon incubation at 37°C ( Hayashi and Matsunaga, 2019 ). Moreover, they start to disaggregate and dissemble after longer exposure to 37°C ( Darriere et al, 2022 ). On the other hand, chilling temperatures lead to the formation of a round structure in the nucleolus.…”