Mutation of an Essential 60S Ribosome Assembly Factor MIDASIN 1 Induces Early Flowering in Arabidopsis

Ribosome biogenesis is tightly associated with plant growth and reproduction. Mutations in genes encoding ribosomal proteins (RPs) or ribosome biogenesis factors (RBFs) generally result in retarded growth and delayed flowering. However, the early-flowering phenotype resulting from the ribosome biogenesis defect is rarely reported. We previously identified that the AAA-ATPase MIDASIN 1 (MDN1) functions as a 60S RBF in Arabidopsis. Here, we found that its weak mutant mdn1-1 is early-flowering. Transcriptomic analysis showed that the expression of FLOWERING LOCUS C (FLC) is down-regulated, while that of some autonomous pathway genes and ABSCISIC ACID-INSENSITIVE 5 (ABI5) is up-regulated in mdn1-1. Phenotypic analysis revealed that the flowering time of mdn1-1 is severely delayed by increasing FLC expression, suggesting that the early flowering in mdn1-1 is likely associated with the downregulation of FLC. We also found that the photoperiod pathway downstream of CONSTANTS (CO) and FLOWERING LOCUS T (FT) might contribute to the early flowering in mdn1-1. Intriguingly, the abi5-4 allele completely blocks the early flowering in mdn1-1. Collectively, our results indicate that the ribosome biogenesis defect elicited by the mutation of MDN1 leads to early flowering by affecting multiple flowering regulation pathways.