The mRNA covalent modification dihydrouridine regulates transcript turnover and photosynthetic capacity during plant abiotic stress

RNA covalent modifications (RCMs) influence RNA stability and translation efficiency, and they thus play critical roles in eukaryotic growth and development. However, their role in regulating plant performance under abiotic stress remains largely unexplored. Here, we integrated multi-omics data in 6 Sorghum bicolor accessions under water-limiting conditions in the field to explore the relationship between RCMs and drought response. Within a stress- and photosynthesis-associated gene co-expression module, we identified SbDUS2, a member of a family of enzymes conserved across eukaryotes, that catalyzes the reduction of uracil to dihydrouridine (DHU) on RNA molecules. DHU-modified transcripts in this module were enriched for photosynthetic functions and showed strong correlation with photosynthetic traits. To elucidate the function of this RCM, we characterized loss-of-function dus2 mutants in Arabidopsis thaliana. Under control conditions, these DHU-deficient mutants exhibited impaired germination and delayed development. Furthermore, under water-limiting or heat conditions, these mutants showed significantly reduced net CO₂ assimilation and survival. Using multiple transcriptome-wide RNA stability assays, we demonstrated that transcripts associated with lower DHU levels in a dus2 background generally exhibited increased stability compared to Col-0 controls. Particularly, lack of DUS2 led to the hyperstability of photosynthesis-related transcripts, impeding their turnover and likely preventing proper photosynthetic acclimation during stress. We propose a model where DHU acts as a critical post-transcriptional regulator marking mRNAs for rapid turnover under stress, highlighting an overlooked regulatory layer contributing to plant resilience.