Arabidopsis group I Pumilio RNA-binding factors are vital for embryo development and balancing growth and stress...

Pumilio (PUM) RNA-binding proteins are crucial for regulating gene expression by binding to a conserved motif in the 3'-untranslated region (3'-UTR). Despite their importance, the role of PUM in plants has been largely unexplored. Here, we investigated the functions of Arabidopsis group I PUMs (APUM1-APUM6), which are ubiquitously expressed and localized in the cytosol. While single apum mutants exhibited no visible phenotypes, CRISPR/Cas9-generated apum1 apum2 apum3 triple mutants (apum1/2/3) displayed reduced growth in both vegetative and reproductive organs, alongside hypersensitivity to various stresses. Remarkably, apum1/2/3/4 quadruple mutants were embryonically lethal, highlighting their essential role in embryo development. Transcriptomic profiling revealed that differentially expressed genes (DEGs) upregulated in apum1/2/3 are enriched in pathways related to stress responses and anthocyanin biosynthesis, while downregulated DEGs are associated with biotic stress defense and hydrogen peroxide metabolism. This suggests that APUM1/2/3 act as molecular hubs balancing plant growth and stress adaptation. Biochemical assays showed that recombinant APUM homologous domains bind to the 5'-UGUGUAUA-3' core motif in the 3'-UTR of the transcription factor Production of Anthocyanin Pigment1 (PAP1), crucial for anthocyanin biosynthesis. Notably, single-nucleotide substitutions, except for the third U, did not affect binding, whereas multiple mutations disrupted interaction. Consistently, apum1/2/3 mutants accumulated significantly more anthocyanin than wild-type plants. Furthermore, we predicted 7,053 potential target genes for APUM1/2/3, of which 1,609 were present among the upregulated DEGs in apum1/2/3. Our findings demonstrate that group I APUMs are vital posttranscriptional regulators, providing perspective on the trade-offs between growth and stress resilience in plants.