RUS6, a DUF647-containing protein, is essential for early embryonic development in Arabidopsis thaliana

The Arabidopsis RUS (ROOT UV-B SENSITIVE) gene family contains six members, each of which encodes a protein containing a DUF647 (domain of unknown function 647) that is commonly found in eukaryotes. Previous studies have demonstrated that RUS1 and RUS2 play critical roles in early seedling development. All six RUS genes are expressed throughout the plant, but little is known about the functional roles of RUS3, RUS4, RUS5 and RUS6.

We used a reverse-genetic approach to identify knockout mutants for RUS3, RUS4, RUS5 and RUS6. Each mutant was confirmed by direct DNA sequencing and genetic segregation analysis. No visible phenotypic differences were observed in rus3, rus4, or rus5 knockout mutants under standard growth conditions, but rus6 knockout mutants displayed a strong embryo-lethal phenotype. Two independent knockout lines for RUS6 were characterized. The rus6 mutations could only be maintained through a heterozygote, because rus6 homozygous mutants did not survive. Closer examinations of homozygous rus6 embryos from rus6/ + parent plants revealed that RUS6 is required for early embryo development. Loss of RUS6 resulted in embryo lethality, specifically at the mid-globular stage. The embryo-lethality phenotype was complemented by a RUS6::RUS6-GFP transgene, and GFP signal was detected throughout the embryo. Histological analyses with the β-glucuronidase reporter gene driven by the RUS6 promoter showed tissue- and development-specific expression of RUS6, which was highest in floral tissues.

Our data revealed that RUS6 is essential for early embryo development in Arabidopsis, and that the RUS gene family functions in multiple stages of plant development.