Dynamics and thermal sensitivity of rRNA maturation paths in plants

Ribosome biogenesis is a constitutive fundamental process for cellular function. Its rate of production depends on the rate of maturation of precursor rRNA (pre-rRNA). The rRNA maturation paths are characterized by four dominant rate-limiting intermediates with cell type variation of the processivity rate. We have identified that high temperature stress in plants, while halting the existing pre-rRNA maturation schemes, also transiently triggers an atypical pathway for 35S pre-rRNA processing. This pathway leads to production of an aberrant pre-rRNA, reminiscent of yeast 24S, encompassing 18S and 5.8S rRNAs that do not normally co-occur together at subunit levels; this response is elicited specifically by high and not low temperatures. We show this response to be conserved in two other model crop plant species (rice and tomato). This pathway persists even after returning to normal growth conditions for 1 h, and is reset between 1 h and 6 h after stress treatment, probably due to resumption of normal 35S pre-rRNA synthesis and processing. The heat-induced ITS2 cleavage-derived precursors and stalled P-A(2)-like precursors were heterogeneous in nature, with a fraction containing polymeric (A) tails. Furthermore, high temperature treatment and subsequent fractionation resulted in polysome and pre-rRNA depletion.