Pre-rRNA processing and its response to temperature stress in maize

Ribosome biogenesis is a fundamental process in all eukaryotic cells and is coupled with the processing and maturation of pre-rRNAs. Maize is the primary staple crop across the world. However, little is known about the exact pre-rRNA processing sites and pathways in maize. In this study, we identified the critical endonucleolytic cleavage sites and detected the pre-rRNA intermediates by circular reverse transcription PCR (cRT-PCR) and northern blot, presenting a detailed model of the pre-rRNA processing pathway in maize. We demonstrated that two pathways coexist in maize to promote the processing of 35S pre-rRNA and that the processing of 27SA pre-rRNA could proceed via two different pathways, which were distinguished based on the order of ITS1 removal and ITS2 cleavage. Compared with yeast and mammals, this new 27SA pre-rRNA processing mechanism is unique to maize and other higher plants. Moreover, we discovered that maize could modulate pre-rRNA processing levels in response to chilling and heat stress, as indicated by the significant reduction of P-A3. Our study should facilitate future research on ribosome biogenesis and pre-rRNA processing in maize.