Arabidopsis mRNA export factor MOS11: molecular interactions and role in abiotic stress responses
TREX (transcription and export) is a multi-subunit complex that links synthesis, processing and export of mRNAs. It interacts with the RNA helicase UAP56 and export factors such as MOS11 and ALYs to facilitate nucleocytosolic transport of mRNAs. Plant MOS11 is a conserved, but sparsely researched RNA-binding export factor, related to yeast Tho1 and metazoan CIP29/SARNP. Using biochemical approaches, the domains of MOS11 required for interaction with UAP56 and RNA-binding were identified. Further analyses revealed marked genetic interactions between MOS11 and ALY genes. Cell fractionation in combination with transcript profiling demonstrated that MOS11 is required for export of a subset of mRNAs that are shorter and more GC-rich than MOS11-independent transcripts. The central a-helical domain of MOS11 proved essential for physical interaction with UAP56 and for RNA-binding. MOS11 is involved in the nucleocytosolic transport of mRNAs that are upregulated under stress conditions and accordingly mos11 mutant plants turned out to be sensitive to elevated NaCl concentrations and heat stress. Collectively, these results establish that mRNA export is critically involved in the plant response to stress conditions and that MOS11 plays a prominent role. Overall design: To investigate export defects in mos11 mutants, RNA was isolated in nuclear and cytoplasmic fractions from wild type Arabidopsis Thaliana (Col-0) and mos11 mutants