Scientists reveal role of RNA helicase in zygote activation and stem cell homeostasis in plants

After double fertilization, zygotic activation occurs that initiates a new life cycle, followed by cell divisions, cell differentiation and organogenesis. During post-embryonic development, stem cells located in shoot apical meristem (SAM) and root apical meristem (RAM) allow plants to continuously generate new tissues and organs. Therefore, understanding the role of zygote activation and stem cell homeostasis is a long-standing interest to scientists.

Recently, researchers led by Prof. Liu Chunming from the Institute of Botany of the Chinese Academy of Sciences (CAS) found that DEAD-box RNA helicase 27 (RH27) plays critical roles in miRNA biogenesis, zygote activation, and stem cell homeostasis.

The Arabidopsis genome has 58 genes encoding DEAD-box RNA helicases, some of which are implicated in RNA-related events including mRNA export, mRNA splicing and rRNA processing. However, the role of DEAD-box RNA helicases in miRNA biogenesis has not been reported in plants.

In this study, a zygote-lethal mutant zyg4-1 was identified, and map-based cloning showed that the mutation was caused by a point mutation in the RH27 gene.

Interestingly, a weak allele of rh27-2 exhibited compromised stem cell homeostasis, in both the SAM and RAM. In rh27-2 plants, the expression of stem cell homeostasis-related genes was up-regulated, alongside with reduced levels of their regulatory miRNAs. Small RNA sequencing and RT-qPCR analyses showed reduced accumulations of a large subset of miRNAs and their pri-miRNAs in rh27-2.

Further biochemical studies revealed that RH27 is associated with pri-miRNAs in vivo and directly interacts with miRNA biogenesis components, DCL1, DDL, HYL1 and SE.

These data together demonstrate that RH27 is a new component of the microprocessor complex, and is required for zygote division and stem cell homeostasis. This work indicates a potential role of miRNA in zygote activation and stem cell homeostasis.

This work was published online in a paper in The Plant Cell titled "DEAD-BOX RNA HELICASE 27 Regulates MicroRNA Biogenesis, Zygote Division and Stem Cell Homeostasis" on November 17.