Coordination between MIDASIN 1-mediated ribosome biogenesis and auxin for modulating plant development.

Ribosomes are required for plant growth and development, and ribosome-biogenesis-deficiency mutants generally display auxin-related phenotypes. Although the relationship between ribosome dysfunction and auxin has been raised, many aspects of this subject remain to be understood. We previously reported that MIDASIN 1 (MDN1) is an essential pre-60S ribosome biogenesis factor (RBF) in Arabidopsis. In this study, we further characterized the aberrant auxin-related phenotypes of mdn1-1, a weak mutant allele of MDN1. Auxin response is disturbed in both shoots and roots of mdn1-1 indicated by the DR5:GUS reporter. Through combining transcriptomic profiling analysis and reporter detection, we found that expression of genes involved in auxin biosynthesis, transport, and signaling is changed. Furthermore, the MDN1 deficiency affects both the posttranscriptional regulation and protein distribution of PIN2 (an auxin efflux facilitator) in mdn1-1 roots. These results indicate that MDN1 is required for maintaining the auxin system. More interestingly, MDN1 is an auxin-responsive gene, and its promoter can be targeted by multiple AUXIN RESPONSE FACTORs (ARFs), including ARF7 and ARF19, in vitro. Indeed, in arf7 arf19, the auxin sensitivity of MDN1 expression is significantly reduced. Together, our results reveal a coordination mechanism between the auxin system with the MDN1-dependent ribosome biogenesis for regulating plant development.