DEAD-box RNA helicase 27-Mediated MicroRNA Biogenesis Is Essential for Zygote Division and Stem Cell Homeostasis in Arabidopsis

Zygote division and stem cell homeostasis are crucial events for plant development. Here, we found that mutations in DEAD-box RNA helicase 27 (RH27) affected zygote division and stem cell homeostasis in Arabidopsis (Arabidopsis thaliana). The strong mutant allele rh27-1 showed a zygote-lethal phenotype, while the weak mutant allele rh27-2 showed defective embryogenesis and compromised stem cell homeostasis in both the shoot apical meristem (SAM) and root apical meristem (RAM). RH27 was expressed in embryos from the zygote stage, and in the SAM and RAM. Cytological analyses revealed that stem cell homeostasis in the SAM and RAM was disrupted in rh27-2. Then, the expression levels of genes related to stem cell homeostasis were elevated in rh27-2, which coincides with down-regulations of their corresponding negative regulatory microRNAs. Furthermore, small RNA-sequencing indicated that the reduction of miRNAs was a global effect in both shoot apices and root tips of rh27-2. Additionally, the accumulation of pri-miRNAs was detected to be decreased. Biochemical studies showed that the nucleus-localized RH27 interacted directly with SERRATE, a component of the microprocessor complex, and DAWDLE, which facilitates the recruitment of substrates to the complex, suggesting that RH27 is a subunit of the microprocessor complex. Overall, this work provides evidences that RH27 regulates zygote division and stem cell homeostasis in Arabidopsis through miRNA biogenesis. Overall design: Small RNA-sequencing and RNA-sequencing were used to study global effects of RH27 on miRNA accumulation and expressions of pri-miRNAs and miRNA targets,respectively.