The rice DEAD-box RNA helicase OseIF4AIIa associates with the CCR4-NOT complex and exhibits stress-responsive...

The CCR4-NOT complex is a major regulator of mRNA metabolism in eukaryotes, yet the contribution of plant DEAD-box RNA helicases to this complex remains insufficiently defined. Rice contains two closely related eIF4AII-like helicases, OseIF4AIIa and OseIF4AIIb, whose evolutionary origins, expression characteristics, subcellular distribution, and molecular interactions have not been comprehensively analyzed.

OseIF4AIIa and OseIF4AIIb were characterized through phylogenetic analyses, expression analyses, fluorescence-based subcellular localization assays, and protein-protein interaction studies. Phylogenetic reconstruction and sequence conservation analyses indicate that the two paralogs likely arose from a recent duplication event within the grasses. Expression analysis showed that OseIF4AIIa is widely expressed in both vegetative and reproductive tissues, with the highest accumulation in nodes, internodes, and leaf sheaths. OseIF4AIIa transcript abundance was strongly induced by salinity and cold, moderately altered by drought, and suppressed by heat. Fluorescent protein fusions demonstrated that both paralogs are restricted to the cytoplasm. BiFC assays further revealed that OseIF4AIIa associates with multiple CCR4-associated factor 1 (CAF1) proteins and interacts with the MIF4G domain of OsNOT1, mirroring the interaction profile of OseIF4AIIb. In addition, CRISPR/Cas9-edited OseIF4AIIa mutant lines exhibited reduced early seedling growth, supporting a role for OseIF4AIIa in vegetative development.

These findings demonstrate that OseIF4AIIa is a cytoplasmic, stress-responsive RNA helicase that engages core components of the CCR4-NOT complex. The close evolutionary relationship and shared interaction partners of OseIF4AIIa and OseIF4AIIb support the possibility of overlapping functions within the eIF4AII-like helicase family in rice. This study advances understanding of helicase-associated mechanisms involved in mRNA regulation under abiotic stress conditions.