RNAi silencing of the Arabidopsis thaliana ULCS1 gene results in pleiotropic phenotypes during plant growth and development

WD40-repeat-containing proteins (WDRs) are highly abundant in all eukaryotes. Several have been implicated as subunits of multi-protein CRL E3 ligase complexes that regulate ubiquitination mediated protein degradation and thus various cellular and developmental processes. Impairment of the WDR protein ULCS1 from Arabidopsis causes pleiotropic phenotypes during plant development, including reduced lignification, anther indehiscence, and sterility. Here we show that RNAi-mediated downregulation of ULCS1 results in a fast-growing phenotype during vegetative development. Due to accelerated growth, ulcs1i mutants reach their vegetative to reproductive transition point earlier than WT plants. However, their comparable germination rate and their similar number of secondary branches and rosette leaves at bolting indicate that ulcs1i is not an early flowering time mutant. GUS staining of progeny, obtained from crosses between ulcs1i and CYCB1::GUS plants, revealed an increased number of mitotic cell divisions in the root meristems of ulcs1i compared to WT. Immunolabeling of homogalacturonans (HGAs) epitopes showed significant fluorescent signal differences at the cell walls and the mucilage of the seeds between ulcs1i and WT. Furthermore, we demonstrate that ULCS1 interacts with the UBA-like protein in a yeast two-hybrid assay, suggesting a direct or indirect physical coupling of these proteins in Arabidopsis.